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APRIL, 1944. Vol. 69. No. 817
T H E A N A L Y S T
P R O C E E D I N G S O F T H E S O C I E T Y O F P U B L I C A N A L Y S T S
; A N D O T H E R A N A L Y T I C A L C H E M I S T S
Th e A n n u a l General Meeting of the Society w a s held at 3.15 p.m. o n W e d n e s d a y , M a r c h 1st, 1944, at T h e Chemical Society’s R o o m s , Burlington House, L o n don, W . l . T h e chair w a s occupied b y the President, Mr. S. Ernest Melling, F.I.C. T h e Financial Statement for 1943 w a s presented b y the H o n . Treasurer a n d a p p r o v e d a n d the Auditors for 1944 were appointed. T h e R ep o r t of the Council for the year ending March, 1944, w a s presented b y the H o n . Secretary a n d adopted. T h e following were elected Officers a n d Council for the c omi n g y e a r :
P r e s i d e n t— S. Ernest Melling, F.I.C.
P a s t P r e s i d e n t s s e r v i n g o n th e C o u n c i l— F. W . F. Arna u d , B e r n a r d Dyer, J o h n Evans, E d w a r d Hinks, E. B. H u g hes, G. R o c h e L ynch, W . H . Roberts a n d G. R u d d T h o m p s o n .
V i c e - P r e s i d e n t s— G. H o g a n , B. G. McLellan, J. R. Nicholls and, e x o f f ic io , W . G o r d o n Carey (Chairman, N o r t h of E n g l a n d Section) a n d A. R. J a m i e s o n (Chairman, Scottish Section).
H o n . T r e a s u r e r— George Taylor.
H o n . S e c r e t a r y— Lewis E y n o n .
O t h e r M e m b e r s o f C o u n c i l— C. A. Bassett, R. C. Chirnside, S. Dixon, R. H . Ellis, J. H. H a m e n c e , H . M . Maso n , (Mrs.) J. W . Matthews, (Miss) M . Pearson, W . H . S i m m o n s , E. Voelcker, G. H . Walker, K . A. Williams and, e x o f f ic io , A r n o l d Lees (Hon. Secretary, N o r t h of E n g l a n d Section) a n d R. S. W a t s o n (Hon. Secretary, Scottish Section).
T h e A n n u a l General Meeting w a s followed b y the postponed Presidential Address of Dr. E. B. H u g hes, w h o w a s unable to deliver it w h e n he retired f r o m the presidential office last year. T h e subject of the Address w a s “ T h e Tec h n o l o g y of Tea.”
Indicating first the world distribution of tea-growing areas, the speaker pointed out that these w e r e not n o w confined to Asia; the necessary tropical or sub-tropical conditions existed elsewhere a n d tea w a s n o w g r o w n extensively in Africa, even as far south as Natal, and also in Russia. In the production of black tea, as distinct f r o m green tea, the m a i n processes are: withering, rolling, fermentation a n d final drying. Withering is a partial natural drying process at as cool a temperature as possible. It dries the leaves to a c o n dition in wh i c h they c an be rolled a n d twisted b y mechanical action simulating rotatory rubbing b e t ween the hands; this d a m a g e s the cells,' whereupon, possibly as a result of
“disorganised respiration,” oxidase of the leaf brings about "fermentation.” This so-called fermentation is mai n l y oxidation of polyphenols of the leaf to quinone c o m p o u n d s , w h i c h readily produce reddish, copper-coloured condensation products. T h e polyphenols of the leaf are the so-called tea tannins, but they are not tannins in the ordinary sense, as they are not able to convert hide into leather. T h e speaker emphasised the i m p o r t a n c e of the rate of "fermentation” o n the quality of the tea produced; if too rapid it gives inferior products, a n d the greater rate of fermentation, c o m b i n e d with lower quality of leaf g r o w n jn hot h u m i d conditions, produces a c o m m o n e r quality of tea. Indeed, the differences )n quality a n d character betw e e n teas f r o m different areas are d u e m a i n l y to differences in geographical a n d climatic conditions, rather than to varietal differences in the plants grown. C h a n g e s in climatic conditions in the s a m e area m a y produce m u c h choicer tea at one time than a m o n t h earlier or later. It is the practice of blending, dependent on the remarkable skill of the tea taster, that enables the c o n s u m e r to be supplied with brands of unchanging character. M o s t g o o d teas, as supplied to the consumer, are blends of m o r e than a dozen lots.
Green tea is not subjected to “fermentation” ;, the enzyme activity is destroyed by heating the leaf (steaming) as soon as possible after plucking, and the leaf is afterwards rolled and “fired”.
105
106 A N N U A L R E P O R T O F COUNCIL: M A R C H , 19*4 N E W M E M B E R S
Wilfred N o r m a n Aldridge; B e n j a m i n Bag s h a w e , A.Met. (Sheff.)*; K e n n e t h Charles Barraclough, B.Sc. (Lond.), F.I.C., A.Met. (SheiL)f; K e n n e t h B o o t h Belcher, Major, A.I.C.;
J o h n H e n r y Bignell, B.Sc. (Lond.); George B r o o m h e a d , B.Sc. (Lond.)*; William B r o w n , A.I.C.; J o h n E d m u n d Chivers; G o r d o n S h a w D o u b l e d a y ; E d w i n E d w a r d s * ; G o r d o n W e s t l a n d E d w a r d s , A.I.C.; William T h o m a s Field, B.Sc. (Lond.), F.I.C.; Eric Arthur Foster; Charles H e n r y H a n d s ; Neil Heron, A.I.C.*; J o h n D o o g o o d Hill, A,Met. (Sheff.)*;
J o h n Douglas H o b s o n , A.Met. (Sheff.)*; William Horner*; T h o m a s William Jones; J o h n Gwilliam Maltby, B.Sc. (Lond.), A.I.C.; Paul Michael M o o n e y , B.Sc. (Lond.), F.I.C.;
G e o r g e Parkin, A.I.C., A.Met. (Sheff.)*; R o n a l d Francis Porter, B.Sc; (Lond.), A.I.C.;
R o g e r Tully Postlethwaite*; William Bennett Price, B.Sc., Ph.D. (Lond.), F.I.C.*;
Alexander Robertson, M.A., B.Sc., Ph.D., M.R.C.V.S.f; M a r c u s Rosebery, B.Sc. (Lond.), A.R.C.S., A.I.C.*; J a m e s E d w i n Sands, A.I.C.*; T h o m a s Arthur Frederick Sexton, B.Sc. (Lond.), F.I.C.; F r a n k Sh a w , M.Sc. (Lond.), D.I.C., A.I.C.; Cyril E d w a r d Spooner, M.Sc.Tech. (Sheff.), A.I.C.*; George Albert Storey, M.P.S.; N o r m a n Strafford, M.Sc. (Lond.), F.I.C.*; Joseph K n i g h t T h o m p s o n , M.Sc., B.Sc.Tech., Ph.D. (Sheff.)*; H a r o l d George Tribley, A.C.G.F.C., F.I.C.; J a c k Tr a s k U n w i n ; Charles Walker, B.Sc. (Lond.), F.I.C.*;
Lionel William W a r ner, A.I.C.; H a r o l d L a w s o n Webster, A.M.C.T., A.I.C.*; Clifford Whalley, B.Sc. (Sheff.)*; Cecil L e e b u m Wilson, M.Sc. (Belfast), Ph.D. (Glasg.)*; K e n n e t h Mackenzie Wilson, A.I.C.; R o n a l d W o o d , M.P.S.*; Leslie W o o d s , M.Sc. (Liv.), A.I.C.*;
Alfred Wright.*
S T A N D A R D S F O R G E L A T I N
Th e Public Analysts a n d Official Agricultural Analysts C o m m i t t e e of the Society has h a d under consideration the question of Standards for Impurities in Edible Gelatin on sale by retail. Consideration has been given to w h a t limits of impurity are obtainable at the present time, a n d the Council has authorised the publication of the following provisional standards pending a n y official regulations.
It is r e c o m m e n d e d that n o action should be taken under the F o o d a n d D r u g s Act, 193S, w h e r e the following quantities are not exceeded:
Arsenic, as arsenious oxide .. 2 parts per million
C o p p e r .. .. .. .. 30 ,, ,, ,,
L e a d .. .. ... .. 10 ,, ,, ,,
Zinc .. .. .. .. 100 ,, ,, ,,
A n n u a l R e p o r t o f C o u n c i l : M a r c h , 1 9 4 4
Th e roll of the Society n u m b e r s 1080, a n increase of 77 over the m e m b e r s h i p a year ago.
T h e Council regrets to h a v e to record the death of the following m e m b e r s : R. M . Clark J. Golding J. A. M a c N a i r H . L. S m i t h L. C o o ksey F. W . J ackson W . G. Messenger K . Wallis M . B. Elliott A. Jaffe H . S. R e d g r o v e S. A. W o o d h e a d Clark, w h o died in his 66th year, h a d been a m e m b e r of the Society for 36 years and served as a m e m b e r of the Council in 1912-13. After completing his course as a student at G l a s g o w LTniversity, he b e c a m e assistant to his father, Dr. J o h n Clark, a n d subsequently succeeded to the practice. H e held appointments as Public Analyst to a n u m b e r of Scottish Counties a n d Burghs.
Cooksey, w h o died at the age of 49, studied at East L o n d o n College, graduating B.Sc.
with first class honours in chemistry in 1915. F r o m then until his death he w a s assistant to Messrs. Rideal a n d Sciver.
Miss Elliott, w h o died in her 59th year, b e c a m e associated with the Society as indexer a n d business manager-of Th e An a l y s t in 1921, a n d unofficial Assistant Secretary in 1922.
In 1937 pressure of other w o r k compelled Miss Elliott to give u p m o s t of her w o r k for the Society and, in recognition of her e m i nent service, she w a s elected a n H o n o r a r y M e m b e r of the Society. (Obituary, An a l y s t, 1944, 69, 33.)
Golding, w h o w a s 72 at the time of his death, h a d been a m e m b e r of the Society for 41 years a n d ’served for t w o periods as a m e m b e r of the Council. Practically the whole
* Through the North of England Section. j Through the Scottish Section.
A N N U A L R E P O R T O F COUNCIL: M A R C H , 1944 107 of liis professional career w a s spent in the service of agricultural chemistry. F r o m 1912 to 1937 he w a s h e a d of the Chemistry D e p a r t m e n t of the National Institute for Research in Dairying, Shinfield. D u r i n g the w a r of 1914-18 he served with great distinction in the A r m y in France. (Obituary, An a l y s t, 1944, 69, 69.)
Jackson, w h o died in his 53rd year, received his scientific training at the Central Technical College, a n d obtained the B.Sc. degree with honours in chemistry in 1911. F r o m 1912 to 1915 he h a d control of the Vinegar B r e w e r y of Holbrooks, Ltd., and, m o r e recently, w a s chemist to Messrs. M a r s h & Baxter, Ltd.
Jaff6, w h o died at the age of 68, h a d been a m e m b e r of the Society for 40 years. H e w a s for over 50 years e ngaged as a consulting a n d analytical chemist in partnership with F. W . Richardson. (Obituary, A n a l y s t , 1943, 68, 199.)
M a c N a i r died at the early age of 36. H e w a s for m a n y years o n the staff of R. R.
Tatlock & T h o m s o n , Public Analysts, a n d w a s lecturer in chemistry at S t o w College, School of Engineering, Glasgow. H e w a s prominently associated with the Scottish Section of the Society.
Messenger, w h o died in his 50th year, h a d been a m e m b e r of the Society for 15 years a nd served as a m e m b e r of the Council in 1926-27. H e obtained the B.Sc. (Birm.) degree with first class honours in chemistry in 1914. D u r i n g the w a r of 1914-18 he served, first in the infantry a n d then in the Special Brigade, R.E. In 1919 he b e c a m e a chemist with J. L y o n s & Co., Ltd., a n d subsequently an assistant chief chemist.
Redgrove, w h o died at the age of 56, w a s a lecturer o n m a t h e m a t i c s a n d chemistry at the R e g e n t Street Polytechnic a n d subsequently at other Institutions. H e w a s an authority o n p e r fumery a n d cosmetics a n d on alchemy. (Obituary, An a l y s t, 1943,68,199.)
Smith, w h o died in his 68th year, h a d been a m e m b e r of the Society for 36 years a n d served o n the Council in 1916-17. H e w a s for s o m e years a lecturer at King's College, London, a n d afterwards Professor of Chemistry in the School of the Pharmaceutical Society;
After the w a r of 1914-1S he w a s chemist to the Scientific Instrument Research Association.
W o o d h e a d , w h o died in his 71st year, h a d been a m e m b e r of the Society for 4 4 years and served as a m e m b e r of the Council in 1911-12. H e b e g a n his professional career as lecturer in chemistry at the Uckfield Agricultural College a n d subsequently b e c a m e Principal. H e afterwards set u p in practice as a consulting chemist a n d bacteriologist and held a n u m b e r of appointments as Public Analyst. (Obituary, An a l y s t, 1943, 68, 297.)
Or d i n a r y Me e t i n g s— In the course of the year five meetings were held and the following papers were communicated:
“ T h e Determination of Fluorine in W o o l treated with Fluorides.” B y F. F. Elsworth, B.Sc., Ph.D., a n d J. Barritt, B.Sc., A.R.C.S., A.I.C.
"Polarographic Studies. III. T h e Determination of V a n a d i u m . ” B y J. E. Page, B.Sc., Ph.D., F.I.C., a n d F. A. Robinson, M.Sc., A . I . C
“T h e Determination of Cantharidin in Beetles a n d Native Medicines.” B y J. C.
Bodenstein, M.Sc.
" T h e Separation of V i t a m i n A f r o m Xanthophylls in the Presence of E g g Y o l k Sterols.”
B y T. B a r t o n M a n n .
" T w o N e w Colour Tests for Stilboestrol.” B y T. Tusting Cocking, F.I.C.
“T h e Determination of C o p p e r Volumetrically b y the Iodine-Thiocyanate M e t h o d . ” B y C. C. Oglethorpe, B.Sc., a n d C. G. Smith, B.Sc., Ph.D., F.I.C.
“T h e Determination of Carotene in Grass a n d Silage Mixtures.” B y T. B a r t o n M a n n .
" T h e R a p i d Determination of Arsenic in Glass.” B y H . N. Wilson, F.I.C.
“Three Pieces of Apparatus.” B y M . A. Fill a n d J. T. Stock, B.Sc., A.I.C.
“ (1) Reflux A p p a r a t u s for A u t o m a t i c Dispersion of Froth in the Determination of Fibre.”
“ (2) A n Electrical Indicator for Collecting a Constant V o l u m e of Distillate.”
"(3) A W a s h Bottle for Delivering Predetermined V o l u m e s of Liquid.”
■ ‘T h e Determination of Indolylacetic Acid.” B y P. F. Holt, Ph.D., D.I.C., F.I.C., a n d
„ H. J. Callow, B.Sc., A.I.C.
.‘A R e v i e w of Micro-Volumetric Apparatus.” B y G. H . W y a t t , B.Sc., Ph.D., F.I.C.
T h e Analysis of C o m m e r c i a l Lecithin.” B y H . H . Hutt, A.I.C., a n d H. Weatherall, F.LC.
A Micro-Method for the Quantitative Determination of Tannin.” B y M . Nierenstein.
D.Sc., Ph.D.
108 A N N U A L R E P O R T O F COUNCIL: M A R C H , 1944
" A n A m p e r o m e t r i c Cell.” B y J. H. Stock, B.Sc., A.I.C., a n d M . A. Fill.
T h e D e c e m b e r meeting w a s a Joint Meeting with the F o o d G r o u p of the Society of Chemical Industry. T h s subject w a s “ Nutrition of the Public a n d F o o d Legislation,”
a n d the following papers were read a n d discussed:
" T h e Essential Natural Nutrients of Fresh a n d M a nufactured Foods.” B y J. C.
D r u m m o n d , D.Sc., F.I.C.
" T h e Rôle of F o o d Legislation in securing A d e q u a t e Nutrition.” B y H. E. Cox, Ph.D., D.Sc., F.I.C.
" T h e Part Played b y the F o o d Supplier in Safeguarding the Nutritive Values of F o o d . ” B y E. B. Hughes, D.Sc., F.I.C.
A t the A n n u a l General Meeting Dr. C. A. Mitchell, M.A., F.I.C., gave an address on
" I n k in Relation to Crime.”
Gr o u p s w i t h i n t h e So c i e t y— P roposals for the formation of G r o u p s within the Society, to deal with special branches of analysis, were considered b y the Council and arrangements for the incorporation of the Microchemical Club a n d for the formation of other G r o u p s were submitted to the Society at the N o v e m b e r meeting a n d approved.
A G r o u p will only be f o r m e d o n the application of m e m b e r s if, in the opinion of the Council, there is sufficient justification for its formation. E a c h G r o u p will h a v e its o w n Chairman, H o n o r a r y Secretary a n d C o m m i t t e e of M a n a g e m e n t . This C o m m i t t e e will arrange periodical meetings and, if desired, joint meetings with other G r o u p s and/or other Societies. Persons wishing to join a n y G r o u p m u s t first join the Society a n d m e m b e r s of the Society are at liberty to join a n y G r o u p or Groups. All m e m b e r s of the Society will be entitled to attend meetings of G r o u p s a n d take part in the deliberations, but only m e m b e r s of a G r o u p will be entitled to vote at meetings of the Group.
Th e An a l y s t— T o c o m p l y with the regulations of the P a p e r Controller each n u m b e r of Th e An a l y s t m u s t n o w contain not m o r e t h a n 32 pages o n the average, a n d it will be noted that the total n u m b e r of pages for the year (388) is in accordance with this c o m putation. Notwithstanding this restriction the n u m b e r of papers published in 1943 (42) exceeds the n u m b e r in 1942 (31), a n d there is a similar increase in the n u m b e r of notes (38 as c o m p a r e d with 30 in the preceding year). This successful condensation of matter into space is largely d u e to the gradual permeation of the “ Advice to A u t h o r s ” issued by the Publication Committee. O n c e m o r e the subject matter of the papers has been fairly evenly distributed b e t ween F o o d a n d D r u g s (15) a n d Inorganic Chemistry (16), a n d the s a m e trend is to be observed in the notes (14 relating to F o o d a n d D r u g s a n d 16 to inorganic subjects). T h e remaining papers a n d notes cover Biochemistry, Bacteriology, Water Analysis, Agricultural Analysis, Organic C o m p o u n d s , Physical M e t h o d s a n d Apparatus.
T o assist Public Analysts a n d Agricultural Analysts w e h a v e continued to d r a w attention to salient points in the various F o o d Orders issued b y the Ministries of F o o d a n d Health.
W e h a v e also been able once m o r e to publish extracts f r o m the Reports of G o v e r n m e n t Analysts in the D o m i n i o n s a n d India, although the issue of s o m e of these w a s suspended until after the war.
H o n. Tr e a s u r e r’s Re p o r t— T he H o n . Treasurer anticipates that the Financial Statement for the year will s h o w a very satisfactory position, probably better even than that of the previous year.
Ex a m i n a t i o n o f Ga s-c o n t a m i n a t e d Fo o d— It has been agreed with the Ministry of F o o d that it w o u l d not be practicable to fix fees but that these should d e p e n d o n the nature a n d circumstances of each case a n d left until the w o r k is carried out.
Fl u o r i n e i n Fo o d s t u f f s— T he Public Analysts a n d Official Agricultural Analysts C o m m i t t e e has r e c o m m e n d e d . m a x i m u m limits for fluorine in certain foodstuffs (Analyst, 1943, 69, 233.)
St a t u s o f Pu b l i c An a l y s t s— A S u b - C o m m i t t e e of the Public Analysts a n d Official Agricultural Analysts C o m m i t t e e has b e e n appointed to consider the future status of the Public Analyst.
An a l y t i c a l M e t h o d s Co m m i t t e e— W ar conditions still restrict the activities of the Sub-Committees, a n d f rom these n o reports h a v e been forthcoming during the year. One n e w S u b - C o m m i t t e e has been appointed to investigate m e t h o d s for determining small a m o u n t s of fluorine in foods a n d is m a k i n g g o o d progress. T h e T o m a t o Products Sub- C o m m i t t e e has been authorised to extend its w o r k to the determination of moisture in other fruit products. A report o n w o r k carried out at the request of the Vitamin Bi
A N N U A L R E P O R T O F COUNCIL: M A R C H , 1944 109 S u b - C o m m i t t e e of the Lister Institute a n d Medical Research Council, o n the Determination of C rude .Fibre in National Flour, w a s published in Th e An a l y s t, 1943, 68, 276.
No r t h o f En g l a n d Se c t i o n— F our meetings h a v e been held during the year a n d the following papers h a v e been read:
“T h e Resazurin Test for Milk.” B y G. Sykes, M.Sc., A.I.C.
" T h e Determination of Arsenic in Glass.” B y H . N. Wilson, F.I.C.
"Quadruplicate Tasting Tests." B y H . M . Mason, M.Sc., F.I.C.
" C o m m e n t s on the Colouring of Fo o d . ” B y D. J. T. Bagnall, A.C.G.F.C., F.I.C.
"Mustard.” B y Dr. J. W . Corran, B.Sc., F.I.C.
“Analysis a n d Research.” B y R. C. Chirnside, F.I.C.
There h a v e been g o o d attendances at the meetings. T h e Section n o w n u m b e r s 160, an increase of 13 o n the previous year.
T h e H o n . Secretary wishes to express his appreciation of the loyal support a n d assistance accorded to h i m b y the C h a i r m a n a n d m e m b e r s of the C o m m i t t e e during the year.
Sc o t t i s h Se c t i o n— T hree meetings were held in the year, at w h i c h the following papers b y m e m b e r s of the Section were read a n d discussed:
“Effluents a n d Fish Life.” B y M . J. R o b b , F.I.C.
" T h e Total a n d R e d u c i n g Sugars in Different Varieties of Potato Tubers, as determined b y the Shaffer a n d H a r t m a n n Iodimetric M e t h o d . ” B y A. M . Smith, Ph.D., D.Sc.
" S o m e Aspects of the Application of F o r m u l a e to the Calculation of Milk Solids.” B y S. M. Boden, B.Sc., A.I.C. (Visitor to the Section.)
"Effect of Electrolytes o n the Freezing Point of Milk.” B y A. R. Jamieson, B.Sc., F.I.C.
" C o n t a m i n a t e d Beverages.” B y J. B. M c K e a n , F.I.C.
T h e C o m m i t t e e record with regret the death of one of our m e m b e r s , Mr. J. A. McNair, F.I.C.
Forty-nine subscriptions were received, being the s a m e n u m b e r as in the previous year.
Four n e w m e m b e r s joined the Parent Society through the Section a n d t w o m e m b e r s resigned on taking u p residence outside the Scottish Area.
In t e r-d e p a r t m e n t a l Co m m i t t e e o n Fo o d St a n d a r d s— T he Council accepted with m u c h regret the resignation of Professor W . H . Roberts, one of the Society’s n o m i n e e s o n the Inter-departmental C o m m i t t e e for F o o d Standards a n d n o m i n a t e d Mr. R. W . Sutton m his place.
Br i t i s h St a n d a r d s In s t i t u t i o n— > M r. S. D i x o n w a s appointed as representative of the Society o n the Technical C o m m i t t e e of the British Standards Institution to prepare standards for filling materials for bedding a n d upholstery. Dr. R. Lessing w a s appointed as representative of the Society o n a C o m m i t t e e to establish standard m e t h o d s for the sampling a n d analysis of boiler waters. Mr. R. Belcher a n d Dr. G. H . W y a t t were a p pointed as representatives of the Society o n a S u b - C o m m i t t e e for the standardisation of microchemical apparatus.
Attendance at meetings of the Council a n d C o m m i t t e e ^ has been well maintained, although travelling conditions h a v e been still m o r e difficult than in the earlier years of the War. T h e Council has again to record its thanks to organisations a n d m e m b e r s of the Society for a c c o m m o d a t i o n a n d hospitality to the Committees.
S. E. M E L L I N G , P r e s i d e n t L E W I S E Y N O N , H o n . S e c r e t a r y
T o l u e n e - 3 : 4 - d i t h i o l a s a S e l e c t i v e R e a g e n t f o r T u n g s t e n : T h e D e t e c t i o n o f T u n g s t e n , e s p e c i a l l y i n M o l y b d e n u m a n d R h e n i u m C o m p o u n d s , a n d i n
F e r r o u s A l l o y s
By C H R I S T I N A C. M I L L E R , D.Sc., Ph.D.
Th e term “ dithiol” w a s first applied b y Clark1 to toluene-3:4-dithiol, 4-methyl-l: 2- mercaptobenzene, w h i c h he used as a reagent for tin, a n d H a m e n c e 2 used the c o m pound as a reagent for tungsten a n d m o l y b d e n u m , with wh i c h it forms bluish-green a n d green complexes, respectively. A t the s a m e time its reactions were under investigation b y p , arW L o w e 3 in the analysis of the tantalum a n d the tungsten gr o u p of N o y e s a n d ray s qualitative scheme. Miller4 found that r h e n i u m also forms a green c o m p l e x with
dithiol. Later,5 she stressed the importance of the reagent for detecting tungsten in association with large a m o u n t s of aluminium, beryllium, c h r o m i u m , uranium, vanadium, zinc a n d phosphate, singly or in admixture. T h e selectivity of the reagent w a s associated with the addition of its soln. in «-butyl acetate to test solns. in w h i c h the concn. of hydrochloric acid w a s high.
T h e m a i n objects of this investigation w ere to extend the expts. o n the detection of tungsten to solns. containing elements other than those cited, a n d to devise a m e a n s for eliminating interference, particularly that of the similarly reacting elements, m o l y b d e n u m a n d rhenium.
It has been found that, in absence of m o l y b d e n u m a n d rhenium, the a b o v e test is of wide applicability for the detection of a few f i g of tungsten, but that there are s o m e inter
fering radicals. W h e n m o l y b d e n u m a n d r h e n i u m are present, a preliminary reduction with stannous chloride suppresses these reactions a n d r e m o v e s s o m e other interfering effects. A modified procedure has been evolved for detecting tungsten in presence of m o l y b d e n u m a n d rhenium, a n d in ferrous alloys. A s the test requires n o preliminary separation of tungstic acid, m a n y other applications are foreseen.
E x p e r i m e n t a l — S i m p l e te st (m o ly b d e n u m a n d r h e n i u m a b s e n t )— T o about 1 m l of the test soln. (in a test-tube, 3 X 3/8 in.), 10-11 N with respect to hydrochloric acid, and containing a drop of orthophosphoric acid to ensure the complete solution of tungstic acid, a d d 0-25 m l of isoamyl acetate a n d c a . 5 m g of dithiol. H e a t in a water-bath at c a . 70° C.
for 5-10 min., shake the tube vigorously at intervals, then a d d a little m o r e dithiol, and heat further for 5 min. T h e colour in the ester layer ranges f r o m pale blue to deep emerald- green for 0-5-25f i g of tungsten. If the t w o layers m e r g e into one, or a m i n o r a m o u n t of tungsten is present, r e m o v e the tube f r o m the bath, a d d 0-5 m l of carbon tetrachloride, shake, centrifuge, a n d r e m o v e a n d reject the upper layer. W a s h the residual layer with conc. hydrochloric acid.
N o t e s o n th e te st— Dithiol does not react appreciably in absence of the ester, which cannot be replaced b y carbon tetrachloride. Heating at 70° C. ensures the quantitative conversion of tungsten without m u c h loss of hydrochloric acid. T h e addition of more dithiol is a safeguard w h e n the ester layer indicates a negative or feeble reaction, a n d w h e n other substances that react with the reagent or that retard the reaction are present. Carbon tetrachloride is a d d e d in preference to water for the restoration of t w o layers, as it does not induce interference b y metals that react with dithiol at lower acidity. T h e solution of the c o m p l e x seems to be very stable, a n d it is permissible to boil off the carbon tetra
chloride in order to concentrate the c o m p l e x in the ester. T h e blue colour obtained with a small a m o u n t of tungsten is highly characteristic. Min o r quantities of m o l y b d e n u m a n d r h e n i u m give green colours. Impurities that give a pale yellow colour occasionally m o d i f y the colour given b y tungsten.
E f f e c t o f v a r i o u s s u b s t a n c e s o n th e d e t e c t io n o f 2¡ i g o f t u n g s t e n b y th e a b o v e m e t h o d— The detection of tungsten w a s considered satisfactory if m o r e than 5 0 % of the a m o u n t added initially w a s indicated a n d the colour h a d a blue tinge. If less than 5 0 % w a s found the sensitivity of the test w a s considered to be reduced.
Addition of 0-25 m l of a n y of the following acids h a d n o important influence:
glacial acetic, formic (90%), h y d r o b r o m i c (4 8 % , bromine-free), hydrofluoric (40%), perchloric (sp.gr. 1-68), orthophosphoric (sp.gr. 1-75), conc. sulphuric (test particularly good). Nitric acid d e c o m p o s e d the reagent, but 5-10 m g could be tolerated. Bromine- free hydr o b r o m i c acid could replace hydrochloric acid entirely. T h e presence of 250 m g of citric, oxalic, or tartaric acid did not prevent the detection of tungsten, but the first t w o lowered the sensitivity. Other acids, tested in 1 0 - m g amounts, were a d d e d as their s o d i u m or potassium salts. Carbonate; cyanide, ferricyanide (more dithiol needed), ferrocvanide, phosphite, sulphide, sulphite, a n d thiosulphate permitted a satisfactory test.
Borate lowered the sensitivity a little. Anions, e .g ., hypochlorite, bromate, chlorate, iodate, iodide, periodate, a n d nitrite, w h i c h d e c o m p o s e the reagent, a n d thiocvanate are easily destroyed before applying the test in a hydrochloric or a hydrochloric a n d sulphuric acid soln. Quantities u p to 1 m g (the greatest a m o u n t tested) of silicate did not influence the detection of tungsten.
In addition to the metals already mentioned, 10 m g (the greatest a m o u n t tested) of the following could be present: lithium, sodium, potassium, rubidium, caesium, silver, m a g nesium, calcium, strontium, barium, c a d m i u m , mercury-11, scandium, yttrium, lanthanum, 110 m i l l e r: t o l u e n e-3 :4-d i t h i o l a s a s e l e c t i v e r e a g e n t f o r t u n g s t e n:t h e
cerium, p r a s e o d y m i u m , n e o d y m i u m , samarium, gadolinium, gallium, indium, thallium1, titanium, zirconium, thorium, g e r m a n i u m , tinj lead, n i o b i u m v, tantalum'-, arsenicv, a n t i m o n y “ 1, b i s muth (colour greener), m a n g a n e s e “ , iron“ , cobalt, a n d nickel. A m m o n i u m ions (10 m g ) were without influence.
N i o b i u m a n d tantalum were present as fluorides in solns. containing 0-25 m l of h y d r o fluoric acid. T h e pptn. of zirconium a n d titanium phosphates, a n d of silver, sodium, potassium, a n d a m m o n i u m chlorides did not prevent the detection of tungsten. Manganese'-“ a n d thallium1“ should be pre-reduced with a little s o d i u m bisulphite, w h i c h is used with advantage also w h e n c h r o m i u m , cerium, a n d v a n a d i u m are in their highest valence states.
Interference in various degrees w a s associated with 10 m g of the following: iron“1, copper“ *DdI, arsenic“ 1,, selenium1'-*0'1''1, tellurium1'*odVI, gold1“ , ruthenium"1, r h o d i u m “1, palladium“ , o s m i u m ' “1, iridium1', a n d platinum1'. T h e yellow colour of the ester-soluble ferric chloride interfered, so that 1 m g of iron with 2/txg of tungsten gave an olive-green colour (c f. Mo). C o p p e r “ reacted with dithiol: 1 m g permitted the detection of tungsten but quartered the sensitivity. Arsenic111 suppressed the reaction with tungsten, but 1 m g could be present if a n excess of dithiol were employed. Selenium a n d tellurium reacted with dithiol but 25-fold excesses were permissible (colours greener). Gold, ruthenium, rhodium, o s m i u m , a n d platinum interfered b y undergoing slow reduction to the elements.
T w o f i g of tungsten could be detected with c a . 250/xg of gold, if the separated metal coagu
lated well, a n d with c a . 1 m g of platinum, 2-5 m g of rhodium, 5 m g of ruthenium, a n d 5 0 f ig of o s m i u m , provided that the period of heating w a s brief. O n e m g of iridium1', wh i c h w a s reduced to iridium1“ , s h o w e d negligible interference, but with 10 m g the sensitivity of the test, w h i c h h a d to be completed within 5 min., w a s lowered. T h e b r o w n dithiol complex of palladium" w a s f o r m e d under the prevailing conditions a n d seriously interfered.
T h e remaining metals of the periodic table were not tried.
M o d i f i e d te st (m o l y b d e n u m a n d r h e n i u m p r e s e n t )— T h e formation of the dithiol c o m plexes of m o d e r a t e a m o u n t s of m o l y b d e n u m a n d r h e n i u m w a s suppressed b y heating the customary test solns. with excess of stannous chloride before adding the ester a n d dithiol.
T h e ester-insol. m o l y b d e n u m 1“ 7 a n d r h e n i u m 1'8 produced did not react with dithiol, but continued heating led to the production in the ester layer, pre s u m a b l y b y re-oxidation in air, first, of b r o w n complexes, a n d later, of the green c o m p o u n d s . W i t h tungsten the blue colour, w h i c h usually appeared, deteriorated to grey-green, but addition of carbon tetra
chloride, brisk shaking, a n d replacement of the stannous chloride layer b y conc. h y d r o chloric acid, restored it.
For the detection of 2/j.g of tungsten with 1 m g of m o l y b d e n u m ' -1 or 0-5 m g of r h e n i u m ' “ the only modification required in the test already prescribed w a s addition of 100 m g of stannous chloride, a n d 5 min. heating at 70° C. before addition of the ester a n d dithiol.
Traces of m o l y b d e n u m a n d r h e n i u m m a d e the colours slightly greener, but the presence of tungsten w a s not in doubt. W i t h 10 m g of m o l y b d e n u m or r h e n i u m c a . 1 0 % of each accompanied the tungsten, a n d it w a s necessary to re-apply the test as follows: Separate and w a s h the soln. with conc. hydrochloric acid, boil off the organic solvents, a d d a drop of phosphoric acid to the residue, a n d destroy organic matter b y heating with a f e w drops of conc. sulphuric acid to w h i c h a drop of conc. nitric acid is a d d e d at intervals. E x p e l the latter, a d d 1 m l of conc. hydrochloric acid, a n d repeat the modified test.
Traces of m o l y b d e n u m a n d r h e n i u m that r e m ained after 2 a n d 3 treatments, re
spectively, could be eliminated b y a n additional treatment w h i c h involved n o loss of tungsten. T h e presence of 0-25 m l of sulphuric or phosphoric acid initially did not influence the reduction process, but perchloric acid counteracted it a n d h a d to be absent. It w a s difficult to find tungsten-free m o l y b d e n u m c o m p o u n d s . S a m p l e s of A n a l a R a m m o n i u m molybdate contained 0-005%.
E f f e c t o f s t a n n o u s c h l o r i d e o n th e d e t e c t io n o f t u n g s t e n i n th e p r e s e n c e o f o th e r m e t a ls— T h e treatment outlined a b o v e effectively eliminated interference with the detection of 2pg of tungsten b y 10 m g of iron1“ , copper“ , arsenic“1, tellurium1' *ndvI, a n d gold?1. It was unnecessary to r e m o v e the elements pptd. f r o m the last three. In the presence of stannous chloride a n d copper1 the blue colour of the tungsten c o m p l e x deteriorated to pale grey, but w a s immediately restored w h e n the carbon tetrachloride layer w a s shaken briskly with -fresh acid. This aeration should never be omitted.
N o tungsten w a s f o u n d after the deposition b y stannous chloride of 10 m g of elementary selenium f r o m selenium1'*“1 % only 5 0 p g of whi c h could be tolerated as such in the test.
D E T E C T I O N O F T U N G S T E N , E S P E C I A L L Y IN M O L Y B D E N U M A N D R H E N I U M C O M P O U N D S 111
112 m i l l e r: TOLUENE-3:4-DITHIOL a s a s e l e c t i v e r e a g e n t f o r T U N G S T E N
Deposition in conc. hydrochloric acid b y m e a n s of sulphur dioxide w a s satisfactory, but, if the stannous chloride w a s afterwards required, it w a s necessary to expel m o s t of the sulphur dioxide a n d restore the high concn. of hydrochloric acid. T h e interference of the precious metals w a s increased, a n d only 25-fold excesses of ruthenium, o s m i u m , a n d iridium could be tolerated. R h o d i u m , palladium a n d platinum h a d to be absent. Interference w a s not anticipated f r o m the majority.of the metallic radicals previously tested. T h e modified test w a s applied successfully in presence of mercury, titanium, vanadium, tantalum, niobium, uranium, p r a s e o d y m i u m , a n d samarium.
D e t e c t i o n o f s m a l l a m o u n t s o f t u n g s t e n i n f e r r o u s a l l o y s— A n y combination of the follow
ing acids, hydrochloric, nitric, phosphoric, hydrofluoric, perchloric a n d sulphuric, is per
missible for effecting solution. A little phosphoric acid should be present, a n d all but traces of nitric a n d perchloric acids ultimately removed. T h e following m e t h o d is ap
plicable to alloy steels a n d cast irons.9 Dissolve 10 m g of steel b y heating in a test-tube with 0-15 m l of phosphoric acid (sp.gr. 1-75) a n d 0-07 m l of perchloric acid (sp.gr. 1-68).
A d d further 0-1 m l of the latter a n d 0-2 m l of sulphuric acid (80%) a n d expel, first, the excess water, a n d then the perchloric acid, w h i c h oxidises the steel c o m p o n e n t s a n d converts the tungsten into silicotungstic a n d phosphotungstic acids. W h e n vigorous ebullition ceases raise the temp, until the sulphuric acid fumes. Allow the tube to cool, a d d 1 m l of conc. hydrochloric acid, a n d proceed with the modified m e t h o d for the detection of tungsten, repeating the treatment if necessary.
R e s u l t s f o r F e r r o u s A l l o y s — S a m ples to w h i c h it w a s intended to a d d / a little tungsten were first analysed alone for tungsten, with the following results: British Chemical Standard— (i) Stainless Steel, No. 209 ( M o = 0 - 0 9 3 % ; n o m e n t i o n of W ) . W found (2 expts., one with 25 mg), c a . 0 - 0 07%. (ii) C a r b o n Steel “ R , ” No. 161 (no W reported b y one analyst in qualitative tests). W fo u n d (2 expts.), 0-02-0-03%. National B ur e a u of Standards, U.S.A.— (i) C h r o m i u m - M o l y b d e n u m Steel, No. 7 2 a ( M o = 0 - 2 0 2 % ; W not detected b y t w o analysts). W fo u n d (2 expts. with 20 a n d 50 mg), c a . 0 - 0 01%. (ii) Nickel- C h r o m i u m - M o l y b d e n u m Cast Iron, No. 107 ( M o = 0 - 6 8 7 % ; W = 0 - 0 0 2 % b y 1 analyst).
W found, c a . 0-005%.
Expts. with 1 0 - m g samples of Nos. 209 a n d 7 2 a were m a d e with addition to tbeir solns. of 2/xg of tungsten in the f o r m of a small portion of a similarly prepared soln. of a tungsten steel. C a . 3/xg a n d 2/tig were found, respectively. W i t h all the alloys containing m o l y b d e n u m a trace entered the organic solvents, necessitating a repetition of the treatment with stannous chloride a n d dithiol in order to ensure the production of the characteristic b lu e colour.
Co n c l u s i o n— T he modified test prescribed for tungsten is so sensitive a n d distinctive,
a n d the conditions of application so favourable, that it w o u l d appear to be suitable for its detection in a variety of materials. T h e stability of the c o m p l e x a n d its ready extraction b y m e a n s of organic solvents suggest that it m a y be suitable for the colorimetric determina
tion of tungsten. Quantitative expts. are under consideration.
Su m m a r y— T oluene-3 : 4-dithiol in ¿soamyl acetate soln. can be used for the detection
of m i n o r a m o u n t s of tungsten'1 in conc. hydrochloric acid solns. containing large excesses of m a n y foreign cations a n d anions. T h e similar reactions of m o l y b d e n u m ' -1 and rhenium'“ can be considerably suppressed, a n d s o m e important interfering effects (e.g., of iron, copper, gold, arsenic a n d tellurium) eliminated, b y reducing the test soln. with stannous chloride before adding the reagent. M e t h o d s are prescribed for the detection of tungsten in m o l y b d e n u m a n d r h e n i u m c o m p o u n d s , a n d in ferrous alloys. A s a preliminary separation of tungstic acid is not required, the test w o u l d appear to be of wide applica
bility qualitatively, a n d perhaps quantitatively.
Re f e r e n c e s
1. Clark, R. E. D., An a l y s t,1937, 62, 661.
2. Hamence, J. H., id., 1940, 65, 152.
3. Miller, C. C„ and Lowe, A. J., J . Chetn. Soc., 1940, 1258.
4. -- Id ., 1941, 792.
5. Id ., 1943, 72.
6.-- --- and Lowe, A. J., id ., 1940, 1263.
7. Noyes, A. A., and Brav, W . C., “A S ystein o f Q u a lita tiv e A n a ly s is f o r the R a r e E le m e n ts ,'’ London, 1927, p. 93.
8. Noddack, I. and W., Z . anorg. Ckem ., 1933, 215, 129.
9. Smith, G. F. and G. P., f . Soc. Ghem. In d .,1935, 54, 1S5t.
Ch e m i s t r y De p a r t m e n t
T h e University, Edinburgh, 9 J a n u a r y , 1944
B O U N D Y A N D MORRIS: D E T E R M I N A T I O N O F R E S I D U A L C A R B O N D I O X I D E 113
D e t e r m i n a t i o n o f R e s i d u a l C a r b o n D i o x i d e i n A e r a t i n g P o w d e r
By C. K . B O U N D Y , A.I.C., a n d R. W . M O R R I S , B.Sc., F.I.C., A.C.G.F.C., D.I.C.
( R e a d a t th e M e e t i n g , A p r i l 5, 1944)
In t r o d u c t i o n— A erating p o w d e r s are evaluated f r o m the available carbon dioxide, which m a y be determined either directly or b y the difference b e t ween the total a n d residual carbon dioxide. Determination of total carbon dioxide presents n o difficulty, but results for available a n d residual carbon dioxide are empirical a n d cannot be precisely stated without reference to the m e t h o d of determination. Direct determination of available carbon dioxide is often preferred, since it represents the real value of the product to the consumer. Deter
mination. of residual carbon dioxide has a n advantage f r o m the analytical point of view, since this figure does not materially alter if the product loses strength o n storage through interaction of the components, although there are complications in certain p o w d e r s w h i c h have suffered serious loss in strength.
T h e F o o d Standards (Baking P o w d e r a n d Gol d e n Raising Powder) Order, 1944, S.R.O. No. 46, prescribes standards for available carbon dioxide in baking p o w d e r a n d golden raising p o w d e r a n d requires that they shall yield not m o r e than 1 - 5 % of residual carbon dioxide, determined in the following m a n n e r : " A sample of 2 g of baking p o w d e r or golden raising powder, as the case m a y be, shall be treated with 25 m l of water a n d evaporated to dryness on a boiling water-bath a n d subsequently treated with a further 25 m l of water a n d evaporated in like mann e r . T h e residual carbon dioxide is the weight thereof evolved w h e n the sam p l e so treated is further treated with excess of dil. sulphuric acid at r o o m temperature, the evolution being completed either b y *boiling or b y m e a n s of reduced pressure.”
T h e purpose of this paper is to s h o w the relationship b e t w e e n the results obtained b y the specified "double evaporation” m e t h o d a n d the calculated excess of s o d i u m bicarbonate for a series of baking powders. A n alternative "salt-reflux” procedure having certain advantages in speed a n d convenience for routine w o r k is also given.
Ex p e r i m e n t a l— M e t h o d s— -The determination of residual carbon dioxide is conveni
ently considered in t w o stages: (1) preliminary treatment for r e m oval of "available” gas, and (2) determination of the "residual” gas. W e are here primarily concerned with the first of these. T h e second stage is in line with the determination of total carbon dioxide and a n u m b e r of satisfactory m e t h o d s are available. Results quot e d in this paper h a v e been obtained using the m e t h o d s of (i) Bagnall, Potter a n d Fleming,1 (ii) Chittick2 a n d (iii) Harley a n d Green.3 T h e three m e t h o d s g ave results in excellent agreement.
T h e m e t h o d quo t e d ab o v e expresses clearly the preliminary treatment for r e m oval of available gas b y the double evaporation m e t hod. A n alternative salt-refiux procedure is in use in our respective laboratories: T w o g of the aerating p o w d e r are boiled with 50 m l of saturated s o d i u m chloride soln. in a 250-ml carbon dioxide flask un d e r reflux for 30 min.
Preliminary expts. with water as reaction m e d i u m h a d s h o w n that the ratio of water to sample, the total water plus sample, a n d the time a n d rate of boiling, could all lead to varia
tions in the result, particularly with p o w d e r s containing acid s o d i u m pyrophosphate. In the salt-reflux m e t h o d it is important that the rate of boiling should be brisk a n d the B u n s e n flame should be adjusted so that the contents of the flask reach b.p. within 4 to 5 min.
T h e flame is then maintained at this height throughout the 30 min. boiling. T h e salt greatly reduces the tendency towards frothing, w h i c h can be completely controlled b y adding a few m g of cetyl alcohol or 1 to 2 m l of a m y l alcohol. T h e size a n d type of the water condenser has n o effect o n the result. T h e salt soln. should h a v e a sp.gr. of c a . 1-20 (Twaddell 40°) a n d its neutrality should be confirmed with b r o m o t h y m o l blue indicator.
T h e salt-reflux procedure has been used for direct determination of available C 0 2 with the apparatus of Bagnall, Potter a n d Fleming,1 a water condenser being introduced after the reaction flask a n d the time of boiling extended to 30 min. Subsequently, residual C 0 2 can be estimated on the s a m e portion of the sample, b y successive acid treatment a n d absorption in fresh portions of b a r i u m hydroxide soln. Bagnall et a l . report that they w e r e unable to repeat their results with sufficient accuracy with the gasometric apparatus of Chittick,2 used in the official A.O.A.C. m e t h o d . W e find that this apparatus
can give reproducible a n d precise results for total C 0 2 a n d for residual CO,, provided that the preliminary treatment in the latter determination is standardised. W e find the apparatus of Hartley a n d G r e e n 3 convenient for determining both total a n d residual carbon dioxide. It is based o n the principle of absorption in b a r i u m hydroxide soln. at reduced pressure, as in the H e p b u r n 4 m e t hod, w h i c h w a s adap t e d for routine w o r k b y Bagnall et a l . 1 Available C 0 2 cannot be determined directly in the Chittick2 apparatus a n d has not been attempted b y the Hartley a n d Gr e e n 3 method.
B a k i n g P o w d e r s— T w o baking p o w d e r s with 1 2 % of total carbon dioxide were prepared, one containing tartaric acid a n d the other acid s o d i u m pyrophosphate, as representing the t w o m a i n classes of aerating powders. T h e tartaric acid h a d a n acidity of 1 0 0 % a n d 100 parts of the acid s o d i u m pyrophosphate were equiv. to 73-5 parts of s o d i u m bicarbonate, both being comparable with commercial materials. T h e baking p o w d e r s were formulated to h a v e a calculated excess balance of 5 % of s o d i u m bicarbonate a n d so to give values for residual carbon dioxide approaching the prescribed limit of 1-5%. This figure of 5 % excess is appreciably greater than w o u l d be considered g o o d trade practice, although a small excess of alkali is usual.
Determinations of residual C 0 2 were carried out on the p o w d e r s as m a d e a n d also with increments of the respective acids calculated so that results were available with sod i u m bicarbonate in excess balance at 5 % , 3 % , 1 % a n d m i n u s 1 % . Further determinations on these p o w d e r s were m a d e with a d d e d increments of s o d i u m bicarbonate to give excess balances of 1 0 % a n d 1 5 % .
S o d i u m B i c a r b o n a t e— T o obtain evidence of its decomposition under the conditions of the present tests, expts. were carried out with s o d i u m bicarbonate alone. Results b y the reflux m e t h o d are s h o w n in Table III as the proportion of the original C 0 2 found as
“ residual,” i. e . , as % retention. T h u s 5 0 % retention represents complete conversion of bicarbonate into carbonate.
Expts. with bicarbonate b y the double evaporation m e t h o d (not included in the table) s h o w e d 5 0 % retention, as w o u l d be expected b y consideration of the details of the procedure. It cannot be a s s u m e d that' the s a m e degree of decomposition takes place in presence of the baking p o w d e r residues.
Re s u l t s— Table I gives the results of the individual determinations. Average figures f r o m this table are entered in Table II a n d are expressed as the retention % of the C 0 2 present in the excess s o d i u m bicarbonate w h i c h w a s found as “ residual." T h e results at the high excesses of 1 0 % a n d 1 5 % s h o w that there is about 5 0 % retention of the C 0 2 in the salt-reflux m e t h o d c o m p a r e d with about 6 0 % in the double evaporation m e t hod. At the lower excess levels of 5 % a n d 3 % this difference is m a s k e d to' s o m e extent because of the ratio of the experimental error to the residual C 0 2 found. A s a consequence, for n o r m a l aerating p o w d e r s there is g o o d agreement b e t w e e n the t w o methods, but products exceeding the limit of 1 - 5 % residual C O , will give significantly higher results b y the double evaporation m e t h o d than b y salt-reflux.
Table II sh o w s that the retention of C O , is less than the 7 5 % reported b y M a c a r a 5 after 30 m i n u t e s ’ boiling under s o m e w h a t different conditions.
Reverting to Table I, it is s h o w n that there is g o o d agreement b e t w e e n the results with the t w o types of p o w d e r at the s a m e calculated excess balance.
Table III gives the results of expts. with s o d i u m bicarbonate only, w h e n boiled under reflux in salt soln. a n d water respectively. Conditions are different f r o m those w h e n baking p o w d e r residues are present; a point of interest is that the retention of C 0 2 is m u c h the s a m e in salt soln. as in water after n o r m a l boiling times, but that retention is greater in the salt soln. o n prolonged boiling. This effect is attributed to suppression of hydrolysis of carbonate a n d bicarbonate ions b y the high concn. of s o d i u m ions. A point of more general interest is the formation of s o m e degree of caustic alkalinity o n boiling a 1 % soln.
of s o d i u m bicarbonate under reflux for 3 hr.
Di s c u s s i o n— A general principle in devising a n empirical m e t h o d of this type is that a n attempt should be m a d e to simulate the conditions under w h i c h the material is to be used.
T h e double evaporation procedure fits in with this principle, since the water treatment m a y be considered c o m parable with conditions in a moist d o u g h or batter a n d the evaporation as corresponding to the baking process. In the reflux method, it m a y be argued that the Use of saturated salt soln. is different f r o m the conditions in a cake batter; but in cake the m e d i u m is certainly not distilled water but a strong soln. of sugar a n d other extractives, 114 B O U N D Y A N D MORRIS: D E T E R M I N A T I O N O F R E S I D U A L C A R B O N D I O X I D E IN
A E R A T I N G P O W D E R 115
Ta b l e I
Percentage residual carbon dioxide
i A_____________________
f — --- — — —
Sodium B y double evaporation B y salt-reflux
bicarb. | * § , *---
balance Individual Aver. Individual Aver.
T a rtra te b a k in g p o w d er Minus 1 % 0-07
003 0-05
0-09 006
nil nil
nil nil
nil
Plus 1 % 0-31 0-18
0-46
0-19 0’28
0-29 0T7
0-22
0-13 0-20
.. 3 % 0-98 0-76
0-97
0-78 0-87
0-91 0-70
0-91 0-74
0-84
0-82
» 5 % 1-40
1-38 1-40 1-38
1-50
1-41
1-34 1-38
1-43
1-22 1-37 1-38
„ 10% 3-15 3-24
3-15
3-18
2-50 2-69
2-55
2-58
„ 1 5 % 4-50 4-50 3-94 3-94
P h o sp h a te b a k in g p o w d e r Minus 1 % 007 0-18
007
0-14 0 11
006 nil
009
nil 003
Plus 1 % 0-28 0-31
0-33
0-30 0-30
0-22 0-18
0-30
0-27 0-28
.. 3 % 0-98 0-87
0-97
0-85 0-92
0-91 0-80
0'88
0-76 O'82
- 5 % 1-40
1-47 1-42 1-46
1-46
1-35 1-42
1-37 1-47
1-47 1-43
1-45
1-44
„ 10% 2-91 3-11
310
3-04
2-50 2-69
2-53
2-57
.. 1 5 % 4-65 4-65 3-85 3-85
Ta b l e II
Residual carbon dioxide t
Sodium bicarbonate balance Double evaporation
A Salt-reflux
A As N a H C 03 C O s equiv.
% %
Found
%
ï r Retention
%
Found V
Retention1 0/
/o /o
T a rtra te b a k in g pow ders
/o /o Jo JO
Plus 3 1-57 0-87 55 0-82 52
„ 5 2'62 1-41 54 1-38 53
„ 10 • 5-24 3-18 61 2-58 49
„ 15 7-85 4-50 57 3'94 50
Ph o sph a te b a k in g pow ders
Plus 3 1-57 0-92 59 0-82 52
„ 5 2-62 1-42 54 1-44 55
„ 10 5-24 3-04 58 2-57 49
„ 15 7-85 4-65 59 3-85 49
Ta b l e III
Residual C 02 as % of original
Bicarbonate--- ,--- *--- * Concentration Time of reflux In salt soln. In water 0-25 g in 50 ml 30 min. 61 62 65 69 0-5 g in 50 ml 30 „ 60 58 59 62 1-0 g in 50 ml 30 „ 60 61 60 62 0-5 g in 50 ml 1 hour 54 — 53 — 0-5 g in 50 ml 3 hours 47 49 43 44
116 B O U N D Y A N D MORRIS: D E T E R M I N A T I O N O F R E S I D U A L C A R B O N D I O X I D E IN
at a p H largely influenced b y that of the flour. It is generally accepted that p o w d e r s based o n acid s o d i u m pyrophosphate give m o r e difficulty than tartrate p o w d e r s w h e n water is used as reaction m e d i u m . T h e s o d i u m chloride in the salt-reflux m e t h o d reduces the hydrolysis of N a 4P 20 7 a n d sharpens the end-point of the reaction, w h i c h is complete at a lower p H than in absence of the s o d i u m chloride. Gerber a n d Miles6 illustrate this effect b y titration curves for pyrophosphoric acid. A t p H 8-4, 9 7 % of the acid is neutralised in presence of 20 g of s o d i u m nitrate per 100 ml, as c o m p a r e d with 7 5 % without the a d d e d salt. A t ¿H'9'l, the degrees of neutralisation are 1 0 0 % a n d 9 3 % respectively. A similar effect occurs in the tartrate powder, as s h o w n b y the lower p H found with b o t h the ex
perimental baking p o w d e r s after reflux with salt soln. as c o m p a r e d with water. This p r o b l e m of hydrolysis is eliminated in the double evaporation m e t h o d b y the actual process of evaporation.
It should be noted that p H results o n solns. of aerating p o w d e r s in water or salt soln.
bear n o relation to p H values for the c r u m b of goods b a k e d with these powders. A n y attempt to correlate the' conditions in a n y such chemical determination with actual baking conditions will be unsuccessful unless it can take into account the acidity a n d buffer action of the flour a n d other ingredients of the d o u g h or batter.
T h e conditions of rate a n d time of boiling m u s t be adhered to in the reflux m ethod, since further loss of C 0 2 b y hydrolysis takes place slowly o n continued boiling. This m e t h o d s h o w s a definite advantage in time a n d attention required over double evaporation, but appears to be less suitable for general w o r k w h e r e analysis of aerating p o w d e r s is not a' routine matter.
Aerating p o w d e r s normally contain a proportion of cereal matter as filler a n d this material m a y h a v e a slight acidity. Maize starch w a s the filler in the baking p o w d e r s used in our expts. a n d the acidity w a s found to be small a n d not to h a v e a n y significant effect o n the results.
Su m m a r y— Official standards h a v e been prescribed for baking p o w d e r a n d golden raising powder. T h e official "double-evaporation” treatment for removal of available carbon dioxide is c o m p a r e d with an alternative "salt-reflux” procedure having advantages in speed a n d convenience for routine work. B o t h m e t h o d s are applied to .baking powders having k n o w n excess of s o d i u m bicarbonate.
Retention of the carbon dioxide present in the excess of s o d i u m bicarbonate is of the order of 6 0 % b y the double-evaporation m e t h o d a n d 5 0 % b y the salt-reflux method.
Results with s o d i u m bicarbonate only, under similar conditions of test, are given.
O u r thanks are d u e to the Directors of Standard B r a n d s Limited, a n d of Messrs.
Pearce, Duff & C o m p a n y , Ltd., for permission to publish this work. W e are also indebted to Dr. J. R. Nicholls a n d Mr. H . E. Jones for information a n d advice.
Re f e r e n c e s
1. Bagnall, H. ft., Potter, R. S., and Fleming, J. K., /. Soc. Chem . In d ., 1939, 58, 127t.
2. Association of Official Agricultural Chemists, " M e th o d s o f A n a ly s is " (5th Ed.), Washington, 1940, p. 186.
3. Hartley, A. W., and Green, A., An a l y s t, 1943, 68, 142.
4. Hepburn, J. R. I., id., 1926, 51, 622.
5. Macara, T., id ., 1915, 40, 272.
6. Gerber, A. B., and Miles, F. T., I n d . E n g . Chem ., A n a l. E d ., 1938, 10, 519.
St a n d a r d Br a n d s, Lt d. Pe a r c e, Du f f & Co., Lt d.
Al d w y c h Ho u s e, Al d w y c h Sp a Ro a d
Lo n d o n, W.C.2 Lo n d o n, S.E. 16
Novem ber, 1943 D i s c u s s i o n
Dr. J. R. Ni c h o l l s confirmed that the authors’ salt reflux method gave results in good agreement with the Official method. H e was particularly interested in the tables showing the relationship between residual carbon dioxide and the excess sodium bicarbonate.
Mrs. G. Di m m i c k asked whether release of carbon dioxide was complete from the hard gelatinous film formed in the double evaporation method. H o w was the difficulty of frothing overcome?
Mr. G. Ta y l o r agreed that both methods gave concordant and reproducible results. H e actually used double evaporation and considered some degree of standardisation of procedure was essential; this point was covered by both methods.
Dr. J. H. Ha m e n c e also confirmed the agreement and emphasised the ease of manipulation in the salt reflux method. H e noted 5 0 % decomposition of the excess sodium bicarbonate compared with 25%
reported by Macara.
Dr. D. C. Ga r r a t t asked whether the authors had any information on the allied subject of determina
tion of residual carbon dioxide in self-raising flour.
