Industrial and Engineering Chemistry : analytical edition, Vol. 3, No. 4

(1)

Analytical

Ed it o r ia l Of f ic e:

R oom 700, Mills Building, Washington, D . C.

T e l e p h o n e : National 0848

C a b l e A d d r e s s : Jiechem (W ashington) Editor: H a r r i s o n E . H o w e

Edition

P u b l i c a t i o n O f f i c e : Easton. Pa.

A d v e r t i s i n g D e p a r t m e n t : 119 Fourth Ave.,

New York, N . Y . T e l e p h o n e : Lexington 2-4180 Assistant to Editor: N . A . P a r k in s o n

V olum e 3 OCTOBER 15, 1931 N u m b e r 4

Improved Technic for Microgravimetric Analyses . . . . P a u l L . K i r k a n d R o d e r i c k C r a ig 345 Determination of Smoking Point of Fats. J o h n M . M c C o y 347 Solubility of Water in Aviation G a s o lin e s...

E l i z a b e t h W. A l d r i c h 348 Determination of Small Quantities of Sulfur and Chlorine

When Present in T u rp en tin e... W. C. S m ith 354 Some Factors Influencing Soap Tests for Hardness .

R. H. K e a n a n d H. G u s t a f s o n 355 Transparent Cellulose Covers for Nessler Comparison Tubes

E . Zim b o n 356 Method for Determination of Small Quantities of Paraform

in Various M ix t u r e s ...W o l t o r W e i n b e r g e r 357 A Dish for Toxicity T e s t s ... A. S. D a n i e l s 358 Sludge Ripeness S t u d ie s ...

E . L. P e a r s o n a n d A. M . B u s w k l l 359 Volumetric Barium Chromate Method for Sulfates . . . .

J. R. A n d r e w s 361 Comparison of Solubilities of Calcium and Strontium p -

Bromobenzoates in Acetone-Water M ix tu r e s ...

J o h n C. B a i l a r , J r . Electrolytic Determination of C o b a lt ...

D o r o t h y H. B r o p iiy 302

A Test for Aldehydes Using Dimethylcyclohexanedione . . Wo l t o r We in b e r g e r

363

365 Method for Determination of Fluorine in Phosphate Rock

and Phosphatic S l a g s ...

D. S. R e y n o l d s a n d K . D. J a c o b 366 Effect of Certain Forms of Silica on Determination of

Fluorine by Volatilization M e t h o d ...

D. S. R e y n o l d s a n d K. D. J a c o b 371 Stillhead for Laboratory C o lu m n s...

E . B. K e s t e r a n d R. A n d r e w s 373 The pH of Butter and Its Relation to Titratable Acidity . .

B. H. N is s e n 374 Improved Gauze-Plate Laboratory Rectifying Column . .

S. Pa l k in 377 Benzidine Method for Determination of Acetic Acid in Lead

A c e t a t e ...J o h n E . S. H a n a n d T . L . C h u 379

383 384

386

387

Entered as second-class matter at the Post Office at Easton, Pa., under the A ct o f M arch 3, 1879, as 40 times a year. Industrial Edition m onthly on the 1st; News Edition on the 10th and 20th; Analytical Edition on the 15th o f January. April, July, and October. Acceptance for mailing at special rate ot postage provided for in Section 1103, A ct o f O ctober 3, 1917, authorized July 13, 1918. . . .,.e maii

Subscription to nonmembers. I n d u s t r i a l a n d E n g i n e e r i n g C h e m i s t r y , ¿7.50 per year. Foreign postage $1.50, except to countnes . 1 American dom estic rates and to Canada. A n a l y t i c a l E d i t i o n only, $1.50 per year, single copies 50 cents, to members 40 cents . . . . J'

$1.50 per year. Subscriptions, changes of address, and claims for lost copies should be referred to Charles L. Parsons, Secretary, Mills g, - ** * D . C. The C ouncil has voted that no claims will be allowed for copies o f journals lost in the mails, unless such claims are recei « notice reouired ) the date o f issue, and no claims will be allowed for issues lost as a result of insufficient notlf * o f change o f address. ( T :*«, nature

“ Missing from files” cannot be accepted as the reason for honoring a claim. I f change of address implies a change of position, p.e • - 20,600 co p ie s o f th is iss u e p rin te d

T h e A m e r i c a n C h e m i c a l S o c i e t y also publishes the Journal o j the. A m erican Chem ical S ociety unà Chemical^Abstra^cts^

(2)

4 A N A L Y T IC A L EDITION Vol. 3, No. 4

MAXI MUM IMPURITIES

M E R C K & CO.

MANUFACTURING CHEMIST

R

a h w a y

, N . J .

• In 1925 the A m e rica n C h em ical Society started p u b lish in g their "R e c o m m e n d e d Specifications fo r A n alytical R e a g e n t C h e m ic a ls” . In these s p e c ific a t io n s th e y d e s ig n a t e th e p e r m i s s i b le m a x im u m o f im purities.

• M e rc k & C o . In c. h a v e alw ays m anufactured chem icals c o n fo r m in g to definite standards, and fo r th e past 2 0 years h av e s h o w n the "M a x im u m Im p u ritie s” o n the lab els o f their analytical c h em  icals. T h e s e ch em icals u sually contain co n sid er

a bly sm aller quantities o f im pu rities than s h o w n o n the la b e l, b u t n ev er m o re .

e T h e p u b lish in g o f definite standards o f purity fo r analytical chem icals by the A m e ric a n C h e m  ical Society has w ith o u t q u estion b een th e m o st p ro gre ssiv e step taken by any g r o u p o f chem ists to w a rd s standardization o f R e a g e n t C h em icals.

• By sp ecifyin g M e r c k ’s, y o u can o b tain ch em  icals o f h ig h u n ifo r m q u ality, c o n fo rm in g to a fixed standard o f m a x im u m im p u ritie s— and in a large n u m b er o f instances c o n fo r m in g to the A . C . S. specifications. W r i t e fo r a c o p y o f the 1931 e d itio n o f M e r c k ’s L a b o ratory C h em ica l C a ta lo g . O r d e r fro m this ca ta lo g and b e sure.

(3)

October 15, 1931 IN DUSTRIAL AN D ENGINEERING CHEMISTRY 5

* A co m p le te _ description o f this apparatus and method of analysis including a review o f the literature on Low Temperature Fractional Distillation Analysis will be found in an article “ Apparatus and M ethods for Precise Fractional Distillation Analysis” b y W alter J. Podbielniak, published in the Industrial and Engineering Chemistry, Analytical E dition, Vol. 3, page 177, April 15, 1931.

# L IS T OF C IR C U L A R S A V A IL A B L E

N o . 4 “ P odbielniak Standard Precision Apparatus— M od el A fo r Low-Tem perature Fractional Distillation Analysis.*’

N o. 5 "Glassblow ing and Construction o f Special Scientific Apparatus.”

N o. 6 "A n alytical, Consulting and Research Service.”

A n n o u n c in g

Podbielniak Standard Precision Apparatus M od el-A

for Low Temperature Fractional Distillation Analysis

The Podbielniak apparatus* is used by practically all o f the m ajor chem ical, natural gasoline, and petroleum companies in the w orld for the complete and accurate analysis o f com plex gaseous and liquid mixtures such as

W E T N A T U R A L GA S A B S O R B E R RESIDU E GA S S T A B IL IZ E R V E N T G A S G A S O L IN E T A N K V A P O R S C R A C K E D R E F IN E R Y GASES

U N S T A B IL IZ E D N A T U R A L G A S O L IN E S P E C IF IC A T IO N N A T U R A L G A S O L IN E LIQ U E F IE D P E T R O L E U M G A S , ALL G R A D E S S T R IP P E D O R E N R IC H E D A B S O R P T IO N OILS M A N U F A C T U R E D GASES O F ALL K IN D S M O T O R FUELS

C O M M E R C IA L S O L V E N T S PRESSU RE D IST IL L A T E S C R U D E P E T R O L E U M

It determines individually all o f the fo llo w in g hydrocarbons and "Other com ponents occurring altogether in one sample w ith an accuracy ranging from a few tenths to a fe w hundredths percent:

H Y D R O G E N

C A R B O N M O N O X I D E N I T R O G E N

O X Y G E N M E T H A N E E T H A N E E T H Y L E N E A C E T Y L E N E C A R B O N D I O X ID E P R O P A N E

P R O P Y L E N E

B U T A N E S BUTEN ES IS O -B U T A N E N -B U T A N E IS O -P E N T A N E N -P E N T A N E PENTENES H E XA N E S H E PTA N E S O C T A N E S A N D

H E A V IE R

_______________ N o. 401

The Podbielniak fractional dijtillation analysis apparatus together with all its modification is fully covered by U. S. and foreign patent applications.

It is manufactured and distributed exclusively by the inventor.

THE NEW STA N D A R D PRECISION MODEL-A of the Podbielniak apparatus while retaining all the advantageous fea

tures of previous models incorporates a great many radical im

provements. The outstanding feature of this new model is its great versatility and flexibility. With only minor adjustments by the operator, it may be used for the analysis of samples rang

ing in volatility from manufactured and natural gases, to motor fuels and absorption oils with fully as much convenience and accuracy throughout as if the apparatus were specifically designed for the particular sample analyzed. The analysis of highly com

plex gases by fractional distillation and supplementary tests is simplified and rendered more accurate by the traction collecting arrangement included in the new model. Greater sensitivity and accuracy have been secured by radical changes in the de

sign of the fractionating columns. The columns arc made in two parts, the distilling tube being entirely separate and remov

able from the slccve-typc vacuum jacket; this construction per

mits the use of any type of distilling tube and bulb best suited for a particular analysis, with a standard vacuum jacket. The dis

tilling tube is free from all bulky seals and therefore from any unnecessary holdup of liquid detrimental to sharp fractionation.

A novel metal reflector replaces the conventional silvering in the vacuum jacket over which it is 50% superior in thermal in

sulation. A new type o f barometric manometer is supplied which can be easily cleaned, refilled with mercury and reevacuated without dismounting from apparatus. The apparatus is rede

signed throughout with many other new features which are fully described in our Circular No. 4.

Incidentally, as a result of the greater demand for the apparatus, it has been possible to make substantial reductions in its price, making it more widely available.

PODBIELNIAK A N ALYTICAL AND RESEARCH LABORATORIES

C a lifo rn ia K r o r m c n t a tiv « : JEIS SEN IN S T R U M E N T CO.

624 E. F ou rth Street Loa A n geles, C a lifo rn ia

12tli F loor M edical Arts BIdg.

TULSA, O KLAHOM A

C ab le Address P o d b ie ln ia k , T u lsa ABC a n d B entley Codes

(4)

A N A L Y T IC A L EDITION Vol. 3, No. 4

C O R N I N G • G L A S S • W O R K S

T last you can be free from the annoyance of discolored Petri Dishes. The new

*P Y R E X

Brand heat resist

ing Culture Dishes are more transparent than fine plate glass, and will remain clear after many washings and sterilizations . . . a distinct aid in laboratory technique.

Rugged in construction, with reinforced edges, it is designed to withstand extremely hard laboratory usage.

The tenacious clearness and rugged construction of

PYREX

Brand Petri Dishes assure both higher laboratory efficiency and greater operating economy.

Your dealer can supply you with these new

PYREX

Culture Dishes promptly.

Size N o. P ieces List p r ice each L ist price

m/m in orig. pkg. in broken pkg. o f orig. pkg.

1 0 0 x 1 5 72 § .50 §36.00

C o v e r on ly 144 .25 36.00

Bottoms on ly 144 -25 36.00

*P Y R E X is a trade-mark and indicates manufacture by C o r n i n c G l a s s W o r k s . C o r n i n g , N. Y.

(5)

October 15, 1931 IN DUSTRIAL A N D ENGINEERING CHEMISTRY 7

DISCOLOR

l ~ h i s r - y \ c ê w ~ p A i r e o c

PETRI D I S H

Unretouched photograph showing the clearness o f a P y re x Brand Petri Dish after being subjected to 20 repeated washings and sterilizations. Washed with a 5 p e r cent solution o f N a3P 0 4, and alloiccd to partially dry without rinsing before each sterilization.

U n retou ch ed p h otog ra p h showing a P y r ex Brand Petri Dish after being subjected to 14 repeated washings and sterilizations . . . it remains clear and unclouded.

P Y R E X • L A B O R A T O R Y • W A R E

(6)

8 A N A L Y T IC A L EDITION Vol. 3, No. 4

S H E P H E R D

G A S A N A L Y S I S A P P A R A T U S

F or the exact analysis o f gaseous mixtures con

taining carbon dioxide, oxygen , carbon m on oxide, m ethane, hydrogen and nitrogen, as designed by M artin Shepherd at the U . S. Bureau o f Standards.

Consisting o f a 100 ml burette graduated in 0.2 ml intervals bu t capable o f being read to 0.05 ml or better, and a m anom eter, b oth m ounted in a water ja ck e t and con nected through a m anifold w ith a sam pling tube and com bustion and absorption pipettes.

T h e glass parts are assembled on a m etal fram e so that firmness o f placem ent and ease o f rem oval are secured. An illum inating system , consisting o f an incandescent bulb m ou n ted on top o f the fram e and adequately screened from the eye o f the observer, with a parallel beam p rojected through a condenser system dow nw ard to a reflecting m irror adjustable vertically and m ounted at 4 5 ° angle to the burette, facilitates ease, rapidity and accu racy in reading the burette. T h e latter is graduated in accordance with the specifications o f the Bureau o f Standards.

T h e construction o f the con trol sto p co ck prac

tically eliminates the danger o f draw ing reagents into the m anifold and facilitates attainm ent o f an accurate pressure balance. T h e m anom eter com bines the features o f a m anom eter and a com pensa

tor and eliminates the significant capillary errors that occu r with som e types o f com pensators.

T h e pressure balance is indicated b y electrical con tact with greater precision and speed than b y the usual m ethods. T h e design o f the water ja c k e t and m ethod o f m ounting the burette and the m anom eter therein elim inate the trouble experienced with the rubber stop p er com m on ly used. T h e m anifold has small capillary dead space and can be easily cali

brated, if necessary.

T h e absorption pipettes are o f the bu bblin g type, com binin g rapidity and efficiency. T h e construc

tion o f the com bustion p ipette overcom es the diffi

culties experienced with other types. T h e platinum com bustion wire is easily replaced. T h e heating current is con trolled b y a slide wire rheostat m ou n ted on the base and is measured b y a W eston amm eter. T h e sam pling pipette perm its con venien t m anipulation o f the sample w ithout contam ination.

See M artin Shepherd, “ A n Im p rov ed A pparatus and M eth od for the Analysis o f Gas M ixtures b y C om bustion and A b sorp tio n ,” Bureau o f Standards Journal o f Research, Vbl. 6, N o. / (Jan., 1 9 3 1), p - 121, re

printed in Bureau o f Standards Research P a per N o. 266, also Am erican Gas Journal, Vol. 13 4^{, N o.}4 (A p ril, 19 3/ ) , p. 49.

5879. Gas Analysis Apparatus, Shepherd, as above described, m ounted on m etal support, co d e com plete with rubber connections and illum inating system for reading the burette. Word W ith one sam pling tube o f 220 ml ca p a city. F or use on 110 v o lts ...$ 250.00 H ylak

Price and specifications subject to change without notice.

ARTHUR H. T H O M A S COMPANY

R E T A IL — W H O LESA LE— E X P O R T

LA B O R A TO R Y APPAR ATU S A N D REAGENTS

W EST W ASHINGTON SQUARE PHILADELPHIA, U. S. A.

Cable Address, “ BALANCE,” Philadelphia 5879

(7)

A nalytical t o â t a i t e M l

G m d

Edition

Published by the ¿American Chem iea/Soeie ty

V olum e 3 OCTOBER 15, 1931 Num ber 4

Improved Technic for Microgravimetric Analyses'

Paul L. K irk and R oderick Craig

Div is io no p Bio c h k m is t k y, Un iv e r s it yof Ca l if o r n ia Me d ic a l Sc h o o l, Be r k e l e y, Ca l i f.

O

F ALL the v a rio u s types of microchemi

ca l a n a ly s e s , those based on determination of the weight of a precipitate seem to offer the g r e a te s t technical difficulties. This is largely owing to the n e c e s s ity of

transferring the precipitate quantitatively from a reaction vessel to a filter, an operation in which small losses are very apt to occur. Such losses are of little importance in macroanalyses, but on a micro scale they may represent a large percentage error.

Obviously there is need for a type of apparatus which will combine the reaction vessel with the filter in such a manner that the transfer of precipitate is either eliminated or rendered easy. It is the purpose o f the authors to describe in this paper a practical apparatus of this nature and a technic for its use in such determinations as those of sulfate, halide, phosphate, etc., all of which are used constantly in both chemical and biological work.

D escription o f Apparatus

Figure 1 shotvs diagrammatically the design of the ap

paratus. A, the reaction chamber, is made from a portion of a test tube attached at the bottom to a heavier tapered tube of smaller diameter, suitable for grinding. In A is a rod, D, hooked at the top and ground into the tapering end of A.

The outside of this tapering end is, in turn, ground into the top of filter tube, B. About a centimeter from the bottom of this ground connection is a platinum plate made from foil about 0.005 inch (0.127 mm.) in thickness. This plate has several small punched holes of 0.5 mm. or less. It fits tightly inside the tube, and after it is in place it is fused to the inside of the glass tube by use of a fine blast flame. The apparatus can be constructed by a glassblower of moderate skill without any serious difficulty. A second rod, E, should be constructed with a hook on the end for removal of the ground rod, D, from its seat. The hooks on both rods must be of sufficient strength to withstand a moderate pull, and for this reason, the size of rod in the hook should be drawn down little if any from the size of the remainder of the rod.

E xperim ental Procedure

In using this type of filter, a fewr points of technic are impor

tant. Dry ground-glass joints nearly always leak a little, and the use of grease in this apparatus is not desirable. Glycerol

1 R eceived March 16. 1931.

was found to be a very suit

able lubricant since it is infi

nitely miscible with water anti a lc o h o l, b u t d is s o lv e s so slowly that the ground glass connections easily retain it almost indefinitely when the parts are pressed together.

A filter pad of asbestos is necessary. This must be of a very good quality and in a proper state of division. Asbestos prepared as for use in the micro calcium method of Kirk and Schmidt (2) is satisfactory. Here a good grade of asbestos washed in acid and ignited was thoroughly dried and ground either in a ball mill, or, more laboriously, by a mortar and pestle, until it was quite fine. If the ground product is sus

pended in water, the fineness will be found easy to grade by the differential rate of settling.

As used in an ordinary gravimetric analysis, such as sulfate or halide, the procedure is as follow's: The disconnected filter tube B is placed in a short stopper in a suction flask. Very mild suction may be produced by use of a pinchcock on the rubber tube to the vacuum line. This may be opened slightly from time to time. In order to make the filter mat properly, the flask of asbestos suspension is shaken and a little of it removed w'ith a pipet having a large orifice, and is run into the filter tube. This gives a thin layer of comparatively coarse asbestos which is sucked down firmly. After a few moments, the coarse asbestos in the flask has settled and some of the fine asbestos is removed with the pipet and run on to the filter until a thin but quite tight filter pad is obtained.

After the usual washing with water several times, it is washed with a small amount of alcohol delivered from a small pipet, and finally in the same way with a little ether. The tube is withdrawn from the stopper, wiped with a soft cloth, and placed in a copper block to reach equilibrium with respect to moisture and temperature. It is weighed on a micro

balance, and then replaced on the suction flask and moistened with a little water which is sucked slowly through. If the filter pad has been properly made and washed, this water will filter through absolutely clear. If it carries through a little asbestos, it should be thoroughly washed as before, redried, and reweighed. This will occasionally save repeating a determination entirely, since loss of any asbestos when filter

ing practically invalidates the result.

In the meantime, the reaction chamber is prepared for the precipitation. The plug D is moistened with glycerol and pressed firmly into its seat in the end of A. In working with An apparatus is described for m icrogravim etric

analyses, such as sulfate, halide, and phosphate de

term ination s, on a very sm all sam ple. T h e tech nic for use o f the apparatus Is described. T h e accuracy is fou n d to be chiefly lim ited by th e possible accuracy o f w eighing and m eth od o f p recipita tion rather than by the apparatus Itself.

(8)

346 A N A L Y T IC A L EDITION Vol. 3, No. 4 different sets of apparatus, a curious fact has come to light.

With some reaction chambers, it is a simple matter to clean them well enough so that precipitate does not cling to the walls. With others, this is exceptionally difficult. In at

tempting to avoid having precipitate cling to the walls, the use of acetone in the solution was found to be remarkably efficient. In the analysis of sulfates, for example, the pre

cipitation is carried out as follows: About 0.5 cc. of pure acetone is used to rinse down the sides of the vessel and the rod D which has already been inserted. This remains in the vessel. Immediately, a little wrater and a few drops of

dilute hydrochloric acid and finally the sample are added.

The sample may be added from a weight buret, a care

fully calibrated microburet, or a micropipet. The chamber A is then dropped into a cut

off test tube which is of the proper length to just contain it, and with an inside di

ameter a bit larger than the chamber A, and which is im

m ersed in a boiling w'ater bath. W h en h ea te d suffi

ciently a few' drops of barium chloride solution are added slowdy with shaking or twirl

ing between the hands. The tube is replaced in the water bath and heated with occa

s io n a l tw ir lin g u n til the barium sulfate is completely coagulated. In the presence of acetone, the coagulation of barium sulfate is very com

plete and rapid, and clinging to the walls is e lim in a te d . With some sets of apparatus it is apparently not necessary to use acetone. The reason for this is still obscure.

In precipitating h a lid e s , less trouble is experienced from clinging to the wralls and usually no difficulty is found in making the precipitation directly in the usual wray.

When the tube .4 is heated sufficiently it is removed and the ground end is moistened with glycerol and inserted into the end of B on the suction flask. The plug is pulled and mild suction applied. The hook E which may have some pre

cipitate adhering, is carefully wuished off with the wash bottle, and the hook of D is hung over the edge of A . The pre

cipitate is of small bulk, and consequently a few washings are sufficient. Without allowing the sides of A to dry and de

posit. any dry precipitate, a small pipet full of alcohol is used to rinse down the sides. This immediately stops the climbing of the precipitate and rinses it quantitatively into the filter from the walls, providing only that the walls have previously been well cleaned with chromic acid, and that the precipitate has been properly coagulated and has not been allowed to dry on the walls. When the last of the precipitate has been re

moved from the walls, .4 is removed from B and laid aside.

The material on the filter and on the ground portion of B is washed further with water and alcohol, and finally with a little ether, to remove all traces of glycerol. The filter is dried as before on a copper block, equilibrated, and weighed.

Originally, it was feared that a trace of glycerol might remain after the final washing, and to assure removal of this, the tube was heated in a regenerating block as described b y Pregl

F igu re 1— D ia g r a m o f A p p a ra tu s (A c tu a l S iz e )'

(8, p. 76) to a temperature of about 200° C. This wras car

ried out on both the empty tube and that containing the pre

cipitate. Later this procedure w'as abandoned since it did not increase the accuracy of the method and required considerably more time.

The filter apparatus has been tested with a number of points in view. Leakage around the ground connections w'ould be serious, but is absolutely eliminated by the use of glycerol. The largest chance for error would seem to be in removal of all the precipitate from the sides of the reaction chamber to the filter. That part of the precipitate which creeps up the sides is very simply washed down by alcohol.

The use of acetone in the mixture prevents quite effectively any tight adherence to the walls. No other agent except dcetone was found for this purpose, although alcohol and glycerol were both tried. However, if the particular type of precipitate cannot be removed by alcohol, the entire ap

paratus may be W’eighed without exceeding the capacity of the microbalance. In either case, policing, with its technical difficulties, is avoided.

R esults

Analyses were run on approximately 0.01 N sulfuric acid solution and 0.01 M potassium chloride solution, and several attempts were made to analyze for minute amounts of sodium according to the method of Barber and K olthoff(f). The results of some typical analyses of sulfuric acid and potassium chloride are given in Table I.

T a b le I— A n a ly ses o f S u lfu r ic A cid a n d P o ta s s iu m C h lo r id e Wt. o f

Co n c e n Or ig in a l

t r a t io n Am t. Wt. op Ma t e r ia l

of o f Pr e c ip i Fo u n d

Sa m p l e Sa m p l e t a t e in Sa m p l e Er r o r Re m a r k s

Cc. Mg. M g. %

SULFURIC ACID®

0.0101 N 5 5 .9 5 2 .5 4 -0 .9 5 W eighed tu b e s ly rica l balan ce

0.0101 N 5 5 .9 0 2 .4 8 + 0 .1 Weighed tu bes

lyrica l ba la n ce

0.0101 Ar 2 2.375 0 .9 9 8 + 0 .7

0.0100 N 1 1.100 0.442 - 0 . 5 3

0.0098 N 2 2.282 0.9588 - 0 . 2 4 U sed a ce to n e 0.0098 N 1 1.150 0.4832 + 0 .3 3 U sed a ceton e 0.009S N 1 .5 1.720 0.7227 + 0 .2 U sed a ceton e

POTASSIUM CHLORIDE^

0.0100 M 1 1.44 0 .7 4 9 + 0 . 4

0.0100 M 2 2 .8 3 5 1.474 - 1.2

0.0100 M 1 1.41 0 .7 3 3 - 1 . 7

0.0100 M 1 1.435 0.746 0

a Precipitate, barium sulfate, b Precipitate, silver chloride.

The weighings were carried out in all cases, except the two noted on Table I, on a microbalance with a sensitivity of about 0.005 mg. The weights of the precipitates amounted in most cases to a little over 1 mg. It is seen immediately that a con

siderable part of the errors observed fell within the error of the balance. The filter tubes average about 2 grams in weight, and in all cases they W'ere weighed with use of a glass tare of practically the same weight. Consequently, it is believed that the limiting factors in the use of this apparatus are, first, the sensitivity of the balance used, and second, small variations due to occlusion of precipitant, solubility of precipitate, and so forth, and are not to any appreciable extent due to inherent difficulties with the apparatus itself.

As stated above, various attempts to use this apparatus for analysis of sodium according to the method of Barber and Kolthoff were made. Although their method is essentially micro in its original form, it is not necessary to use a micro

balance. When samples containing about 2 mg. of sodium were used exactly as they describe, excellent results were ob

tained, but on reducing the sample to between 0.05 and 0.06 mg. of sodium, using this apparatus and the microbalance, erratic and usually low results were obtained. Deviations of from 5 to 25 per cent were common, and no way of adapt

ing the method was found.

(9)

October 15, 1931 INDUSTRIAL AND ENGINEERING CHEMISTRY 347 The advantages of this apparatus over that of Pregl are

several. This one can be used for any method in which he uses the glass filter (3, p. 136) as in halogen and phosphate determinations. It can also be used in place of the micro- Neubauer crucible in the determination of sulfate. An ac

curacy as great as Pregl reports for sulfate determinations is not claimed for this method, for his method of ignition and rewashing is not easily adapted to this apparatus. However, it is felt that an accuracy of =*=0.1 per cent is rarely necessary on such small samples as are here used, and the saving in time and labor is very considerable over his method. In the determination of sulfur by combustion as described by Pregl (3, p. 152), difficulty due to a large volume might be encoun

tered. Since it is only necessary to weight the filter tube B, it is possible to make the reaction chamber A as large as desired so that this difficulty is readily overcome. No loss of precipi

tated barium sulfate through the filter is necessary if it is prop

erly coagulated by heating and the asbestos pad is made from fine enough fiber. This apparatus is decidedly less costly than the micro-Neubauer crucibles and much more simply

manipulated. A much smaller amount of glass is weighed than with Pregl’s glass filter tubes, and here again the manipu

lation is simpler. Likewise, the speed of filtration is decidedly greater, since there are several holes in the platinum disk, each one of about the same diameter as the single hole in the glass filter tube. The amount of asbestos is also smaller.

Many other uses in gravimetric analysis may suggest them

selves. It should, for example, be entirely feasible to earn

out gravimetric calcium analyses by this procedure, if the suggestion of Willard and Boldyreff (4) of igniting the oxalate to carbonate at 450° C. is followed. In biological work, it is frequently desirable to use gravimetric methods for small amounts of organic materials, and here the determination might be simplified by use of this apparatus.

Literature Cited

(1) Barber, H. H., and KolthofF, I. M ., J. Am. Chem. Soc., 50, 1625 (1928) (2) Kirk. P. L., and Schmidt, C. L. A., J. Biol. Chem., 83, 311 (1929).

(3) Pregl, F., "Q uantitative Organische Mikroanalyse,” 3rd ed., Springer, 1930.

(4) Willard. H. H ., and Boldyreff, A. W .. J. Am. Chem. Soc., 52, 1888 (1920)

Determination of Smoking Point of Fats1

Joh n M . M cC oy

M e a t I n s p e c t i o n L a b o r a t o r y , B u r e a u o p A n im a l I n d u s t r y , W a s h i n g t o n , D. C.

T

HE smoking point of a fat is the lowest temperature at which sufficient decomposition takes place to produce visible smoke. As is well known, all fats decompose when heated to sufficiently high temperatures, with the formation of a variety of volatile substances, the most char

acteristic and familiar of which is acrolein. When observed under appropriate conditions, these volatile decomposition products appear as visible smoke.

The significance of the smoking point has been recognized for some time. Blunt and Feeney (I ) studied the factors affecting the smoking point, its bearing on the

utilization of fats, and described a method for its determination. Although this method is suitable for the comparison of different fats, at the same time it docs not take into account all of the factors which may cause variation in the smoking point observed, and on that account is not satisfactory for use by various observers working in different l a b o r a t o r ie s and at different times. A more exactly standardized method is therefore required.

In the work of this laboratory, it has been found desirable to determine the smoking point on a number of samples of fats submitted for examina

tion. As soon as the -work -was undertaken, the need of a standard method became evident. Ac

cordingly, the method described was developed.

The apparatus used, pictured in Figure 1, is sim

ple, the time required for making determinations is short, and the degree of accuracy is sufficient for the purpose.

The method consists in heating the fat under uniform c o n d it io n s until smoke appears, and

noting the temperature. In preliminary experiments it was found that the smoking point is affected by the rate of heating and conditions of observation. Possibly the area of the surface exposed to air is also a factor. In order to attain uniform results, it is necessary, therefore, to heat a definite quantity of fat in a container of standard size

* Received June 22, 1931.

and dimensions and observe the smoke under standard conditions.

Electric heaters of the type commonly used for Kjeldahl digestions (Gilmer heaters) were selected for heating. A rheostat is connected in series with the heaters so that the rate of heating can be reduced as the anticipated smoking point is approached Two heaters are connected in series with the rheostat. The top of one heater is covered with an asbestos plate with a 2'/4-inch (5.71-em.) circular opening in the center, the other by a similar plate with a Vs-inch (2.22-cm.) opening.

The containers used are standard 100-cc. round-bottom flasks, 6 cm. in diameter with 6-cm. neck, and made of Pyrex glass.

To make the smoke more readily distinguishable, a black screen 1 1 X 1 4 inches (27.94 X 35.56 cm.) in size and made of dull black cardboard, such as is used to protect photographic paper from light, is placed directly behind the heaters.

F ißu re 1—View o f A p p a ra tu s

(10)

348 A N A L Y T IC A L EDITION Vol. 3, No. 4 Natural light was found unsuitable on account of its varia

bility. It was found necessary, therefore, to standardize the lighting. Accordingly, the apparatus is set up in a relatively dark place and dependence placed on artificial light. A lamp designed for microscope illumination, equipped with a 100- watt bulb and daylight glass, is used for illumination. The daylight glass renders the smoke more readily visible than it would be by uncorrected artificial light. The smoke point should, therefore, be observed by corrected artificial light.

The apparatus must be set up in a place which is protected from drafts, as even a moderate current of air affects ac

curacy.

P rocedure

Melt the fat, allow moisture and suspended matter to settle out, and filter. Pour 50 cc. of the melted fat into the flask. Set the flask on the heater which has the large opening in the cover plate. Suspend the thermometer from overhead so that the bulb is immersed in the fat, leaving the flask unstop

pered. Heat the fat to between 110° and 115° C. Then remove the flask to the other heater, placing it in such a posi

tion that its open mouth is illuminated by a horizontal beam of light from the lamp and viewed against the black screen. The

lamp should be placed as near the heater as practicable to secure maximum intensity of illumination. Adjust the rate of heating with the rheostat so that the temperature rises at the rate of approximately 2° C. per minute. Take the temperature at which the first wisp of smoke is seen rising from the top of the flask as the smoking point. The first wisp of smoke should be followed by a plainly visible and continuous stream. R e

move the thermometer when smoke is first observed. Smoke should then be seen issuing from the mouth of the flask. If not, replace the thermometer and continue heating until smoke again appears and continues after the thermometer is re

moved. In such case, the temperature at which the second appearance of smoke is noted is taken as the actual smoking point.

The method described has been in use for more than a year and has given satisfactory results. After proficiency has been acquired, duplicate determinations made on separate portions of the same fat should agree within 1 ° or 2° C. Closer agree

ment might be attained by slowing the rate of heating in the final stage.

Literature Cited

(1) Blunt, K ., and Feeney, C., J. Home Econ., 7, 535 (1915).

Solubility of W ater in Aviation Gasolines12

E lizabeth W . A ldrich

B u r u a u o p S t a n d a r d s , W a s h i n g t o n , D. C.

T

HE a m o u n t of water which collects in traps and carburetors is of considerable interest to the operators of automobiles and airplanes. Even after pre

cautions have been taken to remove all suspended water from gasolines, there remain very small amounts of dis

solved water. A decrease in temperature will cause the sepa

ration of some of the dissolved water which, if collected in the fuel feed system over a sufficient period of time, may stop the flow of gasoline to the engine. The flow' may also be inter

rupted by the accumulation of partially hydrated aluminum oxide formed by prolonged contact of water with aluminum fittings. In winter weather, w’ater in the fuel feed system may freeze and damage traps and carburetors.

When water dissolves in a gasoline, the total vapor pres

sure of the gasoline increases by an amount dependent upon the degree of saturation. When saturated, the partial pres

sure of w'ater vapor is not measurably different from the vapor pressure of pure water at the existing temperature. This abnormally large increase in the vapor pressure caused by the presence of small amounts of water indicates the necessity for complete removal of dissolved v-ater or the saturation with w'ater at all temperatures when making accurate vapor-pressure measurements on gasolines. Accordingly, the amount of water required for the saturation of gasolines at various temperatures is of interest. The results of the present study indicate that the solubility at room temperature is about 1 part of w'ater in 10,000 parts of gasoline, from which it may be

5 R eceived M arch 17, 1931. Presented before the Division of Petroleum Chepaistiy at the 81st M eeting o f the American Chemical S ociety, Indian

apolis, Ind., M arch 30 to April 3, 1931.

* Publication approved by the Director of the Bureau o f Standards of the U. S. Department o f Comm erce.

A m eth od is described fo r th e m ea su rem en t o f the solu b ility o f w ater in liq u id p etrole u m p rod u cts, w h ich is ap p licab le to th e d e te rm in a tio n o f traces o f w ater in m an y orga n ic liq u ids. S o d iu m -p o ta ss iu m a lloy free fr o m oxide is added to a w eighed sa m ple o f th e w ater- satu rated liq u id a fter th e rem oval o f dissolved gases.

T h e h ydrogen evolved is collected an d m easu red. Data are given o n th e solu b ility o f w ater in five aviation gaso

lines a t three tem peratu res.

concluded that all commercial gasolines are normally satu

rated with w'ater when used in internal-combustion engines.

Although the solubility of water in gasolines is of interest in connection with a number of problems, very little data on the subject could be found in the literature. Apparently none of the methods previously used for the measurement of the amount of water in solution in gasoline are above criti

cism. Accordingly, an investigation was made of the method based on treatment of the gasoline with an alloy of sodium and potassium and determination of the volume of hydrogen evolved. Data for a number of aviation gasolines were ob

tained.

C h oice o f M eth od

P r e v i o u s M e t h o d s—A number of methods (I) have been described for the measurement of the water in petroleum products. Of these only twro seem to be sufficiently precise for the quantitative determination of the water dissolved in gasolines.

The first of these was used by Groschuff (4), who measured the solubility of water in kerosene, benzene, and paraffin oil. The temperatures were determined at which turbidity appeared and disappeared when known amounts of the liquid and water w'ere cooled and heated in sealed tubes.

In this phase change method it is difficult to determine when all the water is dissolved, since the water tends to stick to the side of the tube. It is also difficult to prevent undercooling.

The second method is that developed by Clifford (3). Air dried over calcium chloride wras bubbled through water- saturated gasoline, and the air and vapors obtained were led through weighed calcium chloride tubes. Gasoline vapors

(11)

October 15, 1931 INDUSTRIAL AND ENGINEERING CHEMISTRY 349

/?

\ /

were then removed by passing dry air through the calcium chloride tubes for several hours. However, the vapor pres

sure of water above calcium chloride is approximately 0.2 mm.

of mercury, so that a loss of water vapor would be expected by this method since, during the period while water is being absorbed in the weighed tube, the dried air is diluted with gasoline vapor and the partial pres

sure of water vapor in it is reduced be

low 0.2 mm.

Checks were obtained on samples con

taining known amounts of water, and it is possible that the loss of water vapor was compensated for by incomplete re

moval of gasoline vapors from the cal

cium chloride tube. However, the gen

erality of this compensation for gaso

lines containing different amounts of water is doubtful.

P r e s e n t M e t h o d— T h e method adopted is a refinement of the method

(1) in which the hydrogen liberated by sodium is used as a measure of the wrater present.

The procedure may be divided into five steps:

(1) The saturation of the sample of gasoline with water by shaking for a predetermined time at a constant temperature.

(2) The transfer of a known weight of water-saturated gaso

line to a suitable container filled with dry air.

(3) The removal from the gasoline of those constituents which exert more than a very small pressure at liquid air tem

peratures.

(4) The introduction of sodium-potassium alloy with re

sultant evolution of hydrogen.

(5) The separation of the hydrogen from the gasoline frozen in liquid air and its measurement in a buret at a determined temperature and pressure.

F ig u re 1— S h a k in g T u b e f o r S a t u r a t in g G a s o lin e w ith W a ter

The advantages of the method which led to selecting it for the present work are:

(а) A very small amount of water will yield an easily meas

urable volume of hydrogen.

(б) It involves only the reasonable assumption that the sole hydrogen-producing reaction is that between water and the alloy.

In principle, it is otherwise free from serious sources of error.

The disadvantages of the present method are:

(a) It is complicated and time-consuming.

(b) The removal of all dissolved gases before the hydrogen is evolved and measured requires special equipment and technic.

(c) Any oxide in the alloy will introduce errors.

In view of these facts, it appears that, although capable of yielding the results required, the method is not especially adapted as a general one for determining the amount of water in gasoline, and that work on simpler methods would probably be more profitable than further development of this one.

Detailed D escription o f Apparatus and Procedure S a t u r a t i o n o f G a s o l i n e s w i t h W a t e r —The shaking tube used for the saturation of the gasolines with water is shown in Figure 1. It is a Pyrex glass bulb of about 100 ml.

capacity, fitted with an inner tube. At the lower end of the inner tube is a small bulb with eight or ten holes about 1 mm.

in diameter. The passage of the gasoline through these holes minimizes the carrying over, during transfer to a second bulb, of any of the undissolved water which settles to the bottom of

F igu re 3 —A p p a ra tu s f o r S a m p lin g W a te r-S a tu ra te d G a s olin e

the shaking tube. To the upper end of the tube is fused a magnetic seal which furnishes a means of transferring a sample of the gasoline to the analytical apparatus. The use of the magnetic seal, which consists of a thin glass tip sealed within a glass tube having a side arm, will be described later.

The shaking tube is sealed to the vacuum system through the side arm A. The vacuum is produced by a rotary pump which is capable of evacuating to approximately 0.001 mm.

of mercury. Further evacuation to better than 0.0001 mm.

may be effected by means of a mercury diffusion pump.

Pressures are read on a McLeod gage connected to the vacuum line.

Approximately 60 ml. of gasoline and 1 ml. of water are introduced into the shaking tube through the side arm B.

The tube is immersed in liquid air, and when the gasoline is frozen, the arm B is sealed off. The space above the gasoline is pumped to a pressure of approximately 0.01 mm., and the bulb sealed from the line at C. Evacuation at this time is necessary to avoid the pressures which would otherwise be developed on shaking the tube at higher temperatures and which would introduce difficulties in transferring the sample to the analytical apparatus.

The tube containing the gasoline and water is placed in a holder and shaken for 4 hours in a thermostated bath held at the desired temperature within 0.1 ° C. A schematic diagram of the shaking mechanism is shown in Figure 2.

In order to determine the time of shaking required to ensure saturation of the gasolines, a number of preliminary experi

ments were made in which samples were shaken with water for various lengths of time. The data on samples of fuel 19 shaken at 30° C. for 1, 2, and 4 hours are given in Table I.

These data show that 1 hour is sufficient to saturate the gaso

line under these conditions. In the solubility measurements, the gasolines were shaken for 4 hours, since a somewhat loDger time might be required for saturation under some conditions.

(12)

350 A N A L Y T IC A L EDITION Vol. 3, No. 4 T o V a cu u m

T r a n s f e r o f W a t e r - S a t u r a t e d G a s o l i n e t o A n a l y t i c a l A p p a r a t u s— After 4 hours of shaking, the tube is rapidly- transferred to a second therniostated bath held at the tem

perature of saturation and regulated to 0.1° C. The ends of the two glass tubes leading from the magnetic seal are broken, a piece of iron inserted above the tip in the vertical tube at D (Figure 3) and this tube sealed. The other arm at D is connected by glass tubing to the bulb F and to the two-way stopcock E, which can be opened either to the vacuum or to the air. Three side arms equipped with magnetic seals are fused to the bulb F, one of them containing a sample of so

dium-potassium alloy. This bulb is weighed before connect

ing it to the line by means of de Khotinsky cement at J .

T able I— W clfiht Per Cent o f W ater in Fuel 19 after Shaking for Various L engths o f T im e

S h a k i n g f o r 1 H o u r S h a k i n g f o r 2 H o u r s S h a k i n g f o r 4 H o u r s

Wt, % Wt. % Wt. %

0.0 0 65 0.0066 0.0074

0.0046 0.0057

0.0061 0.0056

--- 0.0051

____ 0.0056

A v. 0 .0 0 6 5 0.005S 0 .0059

The stopcock E is opened to the vacuum, and the bulb F and the line leading to the tip at D are heated and pumped to remove all moisture. Ordinarily this did not take more than half an hour. Removal of moisture at this time is neces

sary, since the amounts of water which would ordinarily be contained in the air in bulb F would be approximated equal to the amount dissolved in the sample of gasoline.

Dry air is then admitted by opening the stopcock E to the air line. The air is dried by passage through the tube G, containing calcium chloride, the tube II, containing phos

phorus pentoxide, and the bulb I which is immersed in liquid air. The amount of air admitted depends on the vapor pres

sure of the gasoline at the temperature of the bath.

When the vapor pressure is less than 760 mm., the pressure within the bulb F is adjusted until it is slightly less than at

mospheric. The tube at K is broken so that the gasoline in the shaking tube is under atmospheric pressure. The tip at

D is then broken by drawing the piece of iron to the top of the vertical tube by means of a magnet and letting it fall.

Sufficient pressure is applied at K to force a sample of gasoline over into F.

In those cases where the vapor pressure of the gasoline is greater than atmospheric, dry air under pressure is forced into F and the magnetic seal is then broken. The gasoline is drawn over from the shaking tube by gradually reducing the pressure in F until it is slightly less than the vapor pres

sure of the gasoline. When 30 or 40 ml. of gasoline have been collected in F, the stopcock L is closed. The shaking tube is removed from the remainder of the system by breaking the horizontal glass tube connecting it to the bulb F. The broken end of the line is then sealed off. The gasoline in F is frozen in liquid air, the space above it evacuated, and the bulb F sealed from the line at M . F is weighed, together with the glass tube from M to J which is taken from the line by breaking the de Khotinsky seal J. The increase in the weight of the bulb F gives the weight of the gasoline sam

ple.

R e m o v a l o f D i s s o l v e d G a s e s— Those constituents of the gasoline which exert a considerable pressure at liquid air temperatures must be removed, or these gases would be measured together with the hydrogen in the final step of the procedure in which hydrogen is pumped from the frozen gasoline.

The bulb F is con

nected to the vacuum line as shown in Fig

ure 4, th r o u g h the magnetic seal N. A piece of iron is placed in the tube above the t ip at N, an d th is tu b e s e a le d . The space between N and th e s t o p c o c k 0 is evacuated, and after the gasoline in F has been cooled to liquid air temperatures, the tip at N is broken, using a magnet. The air and gases above th e g a s o lin e are pumped off, and with the stopcock 0^closed, th e g a s o lin e is warmed up to room temperature. T h e g a s o lin e is a g a in frozen and pumped.

This procedure is re

peated until the pres

sure above the gaso

line after freezing but before pumping is less than 0.002 mm. The bulb is th e n se a led from the line.

I n t r o d u c t i o n o f

SoDIUM-P OTASSIUM ll>lure

A l l o y— W ith the

gasoline frozen in liquid air, the magnetic seal holding the sodium-potassium alloy is broken and the alloy allowed to run into the bulb. The tube is then sealed off at P . The gasoline is warmed up to room temperature or slightly above, and at intervals is shaken vigorously. The decomposition of the water by the alloy with resultant evolution of hydrogen is

(13)

October 15, 1931 IN DUSTRIAL AND ENGINEERING CHEMISTRY 351 usually complete within 4 or 5 hours. The use of sodium-

potassium alloy involves the reasonable assumption that no gas is evolved by reaction of the alloys with the hydrocarbons constituting the gasoline.

V acuum

F ig u re 6 — A p p a ra tu s f o r P re p a ra tio n o f S o - d lu m -P o t a s s iu m A llo y

F ig u re 7— A p pa ra tu s f o r P u rifica tion o f S o d iu m - P o ta s s iu m A llo y

S e p a r a t i o n a n d M e a s u r e m e n t o f H y d r o g e n—The ap

paratus used for removing the hydrogen from the gasoline and for measuring its volume is shown in Figure 5. The bulb V containing the gasoline and hydrogen is connected through the magnetic seal R to the long inverted U-tube leading to the mercury displacement pump Q, of approximately 200 ml.

capacity. The pump is connected at the bottom to the mer

cury reservoir S which can be opened either to pressure or vacuum through the two-way stopcock T. A capillary tube from the top of the pump joins it to the buret U, graduated in 0.2 ml. The buret is enclosed in a water jacket and is con

nected at the bottom to the mercury reservoir V. This reser

voir can also be opened either to vacuum or to pressure through the stopcock TF. The stopcock X affords a means of transferring mercury from one reservoir to the other by proper adjustment of the pressures. The height of the U-tube above the surface of the mercury in S must be greater than 760 mm. to avoid forcing mercury over into the sample when pressure is applied in S.

The buret and pump are evacuated by opening to the vacuum through the stopcock Y. During evacuation, the pressure in S is adjusted so that the mercury does not rise to the joint with the inverted U-tube. The pressure in V is also adjusted so that the mercury does not close the capillary tubing. When the system is evacuated, the stopcock Y is closed and the mercury in V run up into the buret just above the joint with the capillary tube. The gasoline is frozen in liquid air and the magnetic seal at R broken. Air is admitted through T and the hydrogen in Q is displaced into the buret by the mercury from S. As soon as the mercury has run over into the buret, T is opened to the vacuum and the mercury in Q is drawn back into S. Time is allowed for the diffusion of hydrogen from F into Q, and this in turn is displaced into the buret. This process is repeated until all of the hydrogen above the frozen gasoline is collected in U. The efficiency of the pump depends upon the ratio of the volume of the bulb Q to the volume of the space between the top of the gasoline surface and the point at which the connecting tube joins Q.

In the present case this ratio was approximately 7 to 1.

When all of the hydrogen above the gasoline has been dis

placed into the buret, the mercury in S is run up close to the top of Q. The liquid air surrounding the gasoline is removed and the gasoline allowed to warm up to room tem]>erature.

Care is taken that the pressure of the vapors does not become so high that gas is bubbled through the mercury. This proc

ess liberates additional hydrogen. The gasoline is again frozen and the hydrogen pumped off as before. These opera

tions are continued until no further hydrogen is collected in the buret.

The hydrogen is allowed to stand until it reaches the tem

perature of the water jacket. The stopcock TF is opened to the atmosphere, and the difference between the barometric pressure and the height from the mercury surface in V to the mercury surface in U gives the pressure of the hydrogen.

From the volume of hydrogen under these conditions of temperature and pressure, the weight of water which was dissolved in the known weight of gasoline is computed.

Preparation o f Sod iu m -P ota ssiu m Alloy

Sodium-potassium alloy, rather than either sodium or po

tassium alone, is used to liberate hydrogen from the water dissolved in the gasoline samples, because the alloy, when made up of approximately equal amounts of sodium and potassium, is liquid at room temperatures and can therefore be more easily introduced into the samples. The use of alloy instead of either sodium or potassium alone is also preferable because the liquid alloy maintains a fresh active surface.

Complete evolution of the hydrogen can be accomplished only if the alloy is entirely free from oxides, since the oxides react with water without the liberation of hydrogen. It is necessary, therefore, to remove all oxide from the alloy and to store it in small samples in containers of a design suit

able for introducing it into the gasoline without allowing it to come in contact with air.

Diagrams of the apparatus used in the preparation of the alloy are shown in Figures 6, 7, and 8. The apparatus shown in Figure 6 consists of the three Pyrex bulbs B, C, and D, and the side arm A . The whole system is sealed to the vacuum line. The bulbs are connected by heavy-walled glass tubing or by constrictions, and just above each constriction is placed a fine-mesh copper screen which hinders the passage of oxide while allowing the alloy to pass through. The lower end of bulb D is closed with a magnetic seal. Small pieces of sodium and potassium in approximately equal amounts are

Industrial and Engineering Chemistry : analytical edition, Vol. 3, No. 4

Analytical

Edition

CONTENTS

MAXI MUM IMPURITIES

M E R C K & CO.

MANUFACTURING CHEMIST

R

, N . J .

A n n o u n c in g

Podbielniak Standard Precision Apparatus M od el-A

for Low Temperature Fractional Distillation Analysis

PODBIELNIAK A N ALYTICAL AND RESEARCH LABORATORIES

C O R N I N G • G L A S S • W O R K S

T last you can be free from the annoyance of discolored Petri Dishes. The new

Brand heat resist­

ing Culture Dishes are more transparent than fine plate glass, and will remain clear after many washings and sterilizations . . . a distinct aid in laboratory technique.

Rugged in construction, with reinforced edges, it is designed to withstand extremely hard laboratory usage.

The tenacious clearness and rugged construction of

Brand Petri Dishes assure both higher laboratory efficiency and greater operating economy.

Your dealer can supply you with these new

Culture Dishes promptly.

DISCOLOR

l ~ h i s r - y \ c ê w ~ p A i r e o c

PETRI D I S H

P Y R E X • L A B O R A T O R Y • W A R E

S H E P H E R D

G A S A N A L Y S I S A P P A R A T U S

Price and specifications subject to change without notice.

ARTHUR H. T H O M A S COMPANY

LA B O R A TO R Y APPAR ATU S A N D REAGENTS

A nalytical t o â t a i t e M l

Edition

Improved Technic for Microgravimetric Analyses'

O

Determination of Smoking Point of Fats1

T

Solubility of W ater in Aviation Gasolines12

T

\ /

Brand heat resist