THE APPLICATION OF ROTATING REDUCTORS IN THE DETERMINATION OF IRON
B y W a i . t e r S c o r r R ec e iv e d M a y 23, 1919
IN T R O D U C T IO N
In a form er article1 the efficiency and rap id ity of ro ta tin g m etallic cylinders in th e reduction of vanadic acid h ave been described. I t is the purpose of this paper to g ive an account of the results obtained in a p p lyin g a sim ilar m ethod of reduction in the case of ferric sulfate.
R E D U C T I O N O P F E R R I C S U L F A T E B Y T H E R O T A T IN G Z IN C C Y L IN D E R
In th e first series of experim ents, the results of which are shown in T a b le I, A and B , the reduction was b rou gh t about b y a sm all hollow zinc cylinder into which was fitted a rubber stopper holding an iron spindle, th is being attach ed to the sh aft of a sm all motor which was run b y the ordinary c ity current; T h e motor was fixed to a wooden stand in such a w ay th a t it could be raised and low ered, th us p a rtly immersing the zin c cylin der in the solution to be reduced which was contained in a ta ll narrow beaker. A split glass cover, in which a hole had been m ade sligh tly larger th an the iron spindle, was placed over the top of the beaker. T h e conditions of action were as follows:
T o ta l volum e of solution reduced, 85 cc.; concentrated sulfuric acid, '5 c c .; surface of zinc in contact w ith solu
tion, 25 sq. cm .; source of iron, ferrous amm onium sulfate, the iron content of which had been determ ined b y titratio n w ith perm anganate, standardized against sodium oxalate; the iron solution containing sulfuric
1 G ooch a n d S c o tt, A m . J o u r, S et., 46 (1918), 427.
acid was oxidized previously to reduction b y chlorine gas, the chlorine boiled off, and the iron solution re
duced while hot.
A correction factor of 0.08 cc. of perm anganate was obtained under the sam e conditions as in the experi
m ent, and applied. D ilution was made w ith boiled water.
Ta b l e I A — Pr e l i m i n a r y
Iro n Ir o n
T im e T e m p . of E n d of R ed u c - R ed u c
T e m p . a t T i t r a
—A p p ro x .—.
Vol. N o .
a t of
T i tr a - R ev .
T a k e n F o u n d E rro r tio n tio n tio n tio n p e r
G ra m G ra m G ra m M in. D eg. C. D eg. C. Cc. M in.
0 .0 7 1 3 0 . 0 3 6 4 — 0 . 0 3 4 9 1 83 35 3 0 0 1000
0 .0 7 1 3 0 .0 5 8 1 — 0 .0 1 3 2 2 83 35 3 0 0 1000
0 .0 7 1 2 0 .0 6 4 9 — 0 . 0 0 6 3 3 82 37 3 0 0 1000
0 .0 7 1 3 0 .0 7 0 1 — 0 . 0 0 1 2 4 77 36 30 0 1000
0 .0 7 1 2 0 .0 7 1 0 — 0 . 0 0 0 2 5 76 35 3 0 0 1000
0 .0 7 1 3
B — 0 . 0 7 1 2
-Qu a n t i t a t i v e De t e r m i n a t i o n s
— 0 .0 0 0 1 6 72 35 3 0 0 1000
0 .0 7 1 2 0 .0 7 1 3 - f 0 .0 0 0 1 6 75 37 3 0 0 1000
0 .0 7 1 3 0 .0 7 1 5 - f 0 .0 0 0 2 6 75 3 4 3 0 0 1000
0 .0 7 1 2 0 .0 7 1 3 +0 . 0 0 0 1 6 75 37 3 0 0 1000
These results indicate th a t the reduction of the sm all am ounts of iron taken is com pleted regu larly under the given conditions w ithin a period of 6 min.
IN C R E A S E I N R E D U C I N G S U R F A C E
For the experim ents in T a b le I I , A , B , and C , a larger cylinder was made and the iron spindle fixed d irectly in the zinc. T h is sam e ty p e of zinc cylinder has been used in all th e experim ents w hich follow .
T he conditions under which the results in T ab le II were obtained were the follow ing: T o ta l volum e of solution reduced, 60 cc.; concentrated sulfuric acid, 5 cc.; surface of zinc in co n tact w ith solution, about 45 sq. cm .; source of iron, its content, reduc
tion, and oxidation the sam e as in T a b le I. A correc
tion factor of 0.10 cc. of perm anganate was obtained
T H E J O U R N A L OF 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 Vol. n , No. 12
Dec., 1919 T H E J O U R N A L OF 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 I I 3 7 after oxidation the excess of chlorine was boiled oS.
W hile the solution was still a t the boiling tem perature the zinc cylin der was low ered into it and rotated for the periods indicated. T h e reduced solution was poured into a 1500-cc. evap o ratin g dish, 7.5 cc. con
cen trated sulfuric acid added, the volum e made up to a liter w ith ordinary distilled w ater, and titrated . T h e perm anganate was m ade of such strength as to obtain com plete oxidation w ith less than 100 cc. to avoid refilling the bu rette. T h e zinc cylinder was of such dim ensions as to get a contact surface of ab out 75 sq. cm.
R E D U C T I O N O F L A R G E A M O U N T S O F IR O N U S IN G R O T A T IN G Z IN C A N O D E
T h e eq u ivalen t valu e of 1 cc. of perm anganate ( N / 10 X 1.4 approxim ately) in terms of iron was determ ined in a sim ilar w a y to th at used in T ab le IV . T h e zinc was m ade th e rotatin g anode and a piece of platinum foil, 5 cm. X 10 cm ., was the station ary cathode. T h e current used 'measured 6 amperes.
O ther conditions were th e sam e as in the experiments of T a b le IV .
Ta b l e V
A — P r e l i m i n a r y D e t e r m i n a t i o n s (R é d u c tio n s ta r te d a t boiling te m p e ra tu re )
T im e o f A pprox. A pprox.
I r o n Ir o n R ed u c - T e m p , a t N o . of Vol. a t T a k e n F o u n d E r r o r tio n T i tr a tio n R e v . T itra tio n G ra m G ra m G ra m M in . D eg. C . p e r M in . Cc.
0 .7 0 6 5 0 .6 4 5 2 — 0 .0 6 1 3 1 26 700 1000
0 .7 0 6 5 0 .7 0 4 6 — 0 .0 0 1 9 2 26 700 1000
0 .7 0 6 5 0 .7 0 5 5 — 0 .0 0 1 0 3 26 700 1000
B — Q u a n t i t a t i v e D e t e r m i n a t i o n s (R e d u c tio n s ta r te d a t b o iling te m p e ra tu re )
0 .7 0 6 5 0 .7 0 6 0 — 0 .0 0 0 5 3 24 700 1000
0 .7 0 6 5 0 .7 0 6 6 + 0 .0 0 0 1 3 22 700 1000
0 .7 0 6 6 0 .7 0 6 0 — 0 .0 0 0 6 3 22 700 1000
0 .7 0 6 6 0 .7 0 5 8 — 0 .0 0 0 8 3 21 700 1000
0 .7 0 6 5 0 .7 0 6 1 — 0 .0 0 0 4 3 21 700 1000
0 .7 0 6 6 0 .7 0 6 7 + 0 .0 0 0 1 3 22 700 1000
T h e results of T ab les I V and V show th a t large am ounts of iron as ferric sulfate in dilute sulfuric acid solution, and also containing sm all am ounts of hydrochloric acid, are rap id ly reduced both w ith and w ith ou t the electro lytic current, the tim e of reduction being sligh tly less when the electrolytic current is used.
T h e correction fa cto r and th e use of boiled w ater were elim inated in this set of experim ents b y the m ethod described above for the standardization of perm anganate.
R E D U C T IO N O F S M A L L A N D L A R G E A M O U N T S O F F E R R I C S U L F A T E B Y R O T A T I N G A L U M IN U M T U B E A N D B Y
R O T A T I N G A L U M IN U M A N O D E
In the experim ents of T ab le V I a good grade of alum inum pipe was su bstitu ted for the zinc cylinder.
T h e hollow tub e of alum inum was attached to the sh aft of the m otor b y an iron spindle which was in
serted into a rubber cork, and the cork into the tube.
W hen th e electrolytic current was used, connection betw een the spindle and tub e was made b y means of a sm all piece of sheet platinum . A correction factor of o.2o cc. of perm anganate was obtained and was used in the q u an titative determ inations.
T h e conditions of the experim ents in A were the sam e as in the experim ents of T ab le II, except th at the am ount of concentrated sulfuric acid added was 4 cc., th e total volum e reduced was 52 cc., and the surface of contact w ith the alum inum was 70 sq. cm.
T he conditions of the experim ents in B and C were th e same as in the experim ents in T a b le I I I , excep ting th a t the am ount of concentrated sulfuric acid was 4 cc., the total volum e reduced 52 cc., and the surface of con tact w ith the alum inum 70 sq. cm.
T h e conditions of the experim ents in D were ex
a c tly the sam e as in A except th a t large am ounts of ferric sulfate were used.
T a b l e V I A — P r e l i m i n a r y
(R e d u c tio n s ta r te d a t b o iling te m p e ra tu re w ith o u t th e e le c tro ly tic c u rre n t) T im e T e m p . N o . Vol.
of a t of a t
Iro n Iro n R e d u c - T itra - R e v . T i tr a A m -T a k e n F o u n d E r ro r tio n tio n p e r tio n peres G ra m G ra m G ra m M in . D eg. C . M in . C c. U sed
0 .0 7 1 6 0 .0 1 4 5 — 0 .0 3 0 1 1 29 700 300 0
0 .0 7 1 6 0 .0 6 5 7 — 0 .0 0 5 9 3 29 700 300 0
0 .0 7 1 6 0 .0 7 0 6 — 0 .0 0 1 0 4 30 700 300 0
0 .0 7 1 6 0 .0 7 1 6 0 .0 0 0 0 5 26 700 300 0
B — Pr e l i m i n a r y
(R e d u ctio n s ta r te d a t b o iling te m p e ra tu re w ith th e e le ctro ly tic c u rre n t)
0 .0 7 1 6 0 .0 5 5 9 — 0 .0 1 5 7 1 31 700 300 6
0 .0 7 1 6 0 .0 7 1 5 — 0.0 0 0 1 2 28 700 300 6
, C — Q u a n t i t a t i v e
(R e d u c tio n s ta r te d a t boiling te m p e ra tu re w ith th e e le ctro ly tic c u rre n t)
0 .0 7 1 6 0 .0 7 1 6 0 .0 0 0 0 2 .5 30 800 300 6
0 .0 7 1 6 0 .0 7 1 6 0 .0 0 0 0 2 .5 28 800 300 6
0 .0 7 1 6 0 .0 7 1 6 0 .0 0 0 0 2 .5 30 800 300 6
0 .0 7 1 5 0 .0 7 1 6 + 0 .0 0 0 1 2 .5 27 800 300 6
0 .0 7 1 6 0 .0 7 1 5 — 0.0 0 0 1 2 .5 32 800 300 6
D — P r e l i m i n a r y f o r L a r o e A m o u n t s
(R e d u c tio n s ta r te d a t bo ilin g te m p e ra tu re w ith o u t th e e le c tro ly tic c u rre n t)
0 .7 1 5 0 0 .6 5 7 0 — 0 .0 5 8 0 1 24 800 1000 0
0 .7 1 5 0 0 .6 9 9 5 — 0 .0 1 5 5 2 23 800 1000 0
0 .7 1 5 0 0 .7 0 9 1 — 0 .0 0 6 9 3 26 800 1000 0
T h e experim ents made w ith alum inum seemed to indicate th a t th e reduction brought about b y this m etal is som ew hat more rapid th an th a t b y zinc, either w ith or w ithout the aid of the electrolytic current. T h e difficulty in obtaining alum inum of the necessary degree of p u rity has, how ever, prevented, for the tim e at least, the q u an titative stu d y of the use of alum inum in the reduction of larger am ounts of ferric sulfate.
C O N C L U S IO N
T he results show th a t ferric sulfate, in either small or large am ounts, m ay be rap id ly and efficiently reduced b y rap id ly rotatin g reductors of zinc or alum inum , either w ith ou t or w ith the aid of the electrolytic current; and th a t q u an titative results m ay be obtained b y titration of the reduced ferrous salts w ith p o ta s
sium perm anganate.
T he reducing action of the rotatin g zinc cylin der exposing a considerable area of action (75 sq. cm.) to solutions of ferric salts of suitable volum e (50 cc.) affords a rapid and exact altern ative to reduction b y the am algam ated zinc colum n of th e Jones reductor, the rap id ity of reduction depending largely upon the area of the reducing surface of the zinc, th e tem perature, 'and the volum e of th e solution. B y this m ethod it should be possible to determ ine w ith rap id ity, con
venience and exactness th e to ta l conten t of iron in sulfate or chloride solutions of ferric salts obtained b y any of the usual processes from the m etal or an ore.
A C K N O W L E D G M E N T
T h is w ork was done at the K e n t C hem ical L ab o rato ry of Y a le U n iversity in 1918, and th e w riter wishes to th an k Prof. F . A. G ooch, who suggested the problem , and whose advice at all tim es has been m ost helpful.
Ak r o n, Oh io
i i 3 8 T H E J O U R N A L OF 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 Vol. i x, No. 12 THE PERMANGANATE METHOD FOR COPPER
B y L o u i s F . C l a r k R ec e iv e d J u ly 2, 1919
A lm ost e v e ry works lab o rato ry em ploys some m ethod of control analysis w hich although know n to be th eoretically in exact y e t yields results sufficiently correct for all p ractical purposes. U sually, in such cases, expediency is placed before th eory and dis
crepancies accoun ted for b y a rb itrary adjustm ent.
If, how ever, b y a slight change in procedure, such an expedient m ethod can be brou gh t more nearly into th eoretical line, the change w ould seem to be justified.
In th e copper lab orato ry, such an expedient m ethod is th a t know n as the “ p erm an ganate,” and although know n to be th eoretically inexact, y e t it m ay be so adju sted b y fa cto r or graph correction th a t it is ac
cepted as a useful control determ ination. W hen so em ployed, th e usual procedure involves the precipi
tation of th e copper as cuprous th io cya n a te from an acid solution, follow ed b y such tre atm en t of the pre
cip itate th a t a solution of the th io cya n a te ion is o b tain ed and a residue containing the cuprous ion left on th e filter paper. T h e th io cy a n a te solution is acidified and oxidized b y perm anganate. T h e de
tails of th e procedure can be found in the te x t of Lord and D em orest, page 210. T h e alkalin e titratio n suggested b y these authors is not u su ally practicable, and when acid solution is used a correction fa cto r is necessary.
T h e reactions in volve d in the usual procedure, assum ing proper precip itation of cuprous th io cyan ate, are:
x— D ecom position of the cuprous th io cya n a te pre
cip itate b y hot solution of cau stic soda, th ere b y leaving th e cuprous ion on the filter paper as insoluble cuprous hydroxide. T h e th io cya n a te ion passes into solution as sodium th io cyan ate, according to the eq u a tio n :
C u C N S + N aO H = C u O H + N a C N S (1) 2— T h e solution is acidified and titrated w ith per
m anganate, the equation for the reaction being S H C N S + 6K M n04 + 4H 2S04 =
3 K 2S04 + 6M n S04 + s H C N + 4 H20 (2) F rom the equation,
2 K M n O ( -I- io F e S04 -I- 8H2S04 =
K 2S04 + 2 M n S 0 4 + sF e 2S04(3) + 8H20 we m ay w rite,
6K M n04 = 30 Fe, and from E q u atio n s 1 and 2 S H C N S = s C u = 6K M n04 = 30 F e, or,
1 C u = 6 Fe, whence,
C u : 6 F e = 63.57 : 335.04, or C u = 0.1897 Fe (Fe value of th e perm anganate).
H ow ever, the oxidation does not a ctu a lly proceed as indicated b y the above equation, b u t only approxi
m ates th e theoretical relation. Furth er, th e approxi
m ation does n ot seem to be close enough to a linear function so th a t a definite coefficient can be determ ined for a wide range of copper values. T h u s graphs are som etim es used to more closely approxim ate th e tru th . Others sim p ly increase the th eoretical factor 0.1897
to valu es ranging from 0.1950 up to 0.2100, depending upon in d ivid ual experience.
One a u th o rity 1 states th a t the oxidation of thio- cyan ic acid b y potassium perm anganate proceeds according to the aforem entioned equation w hen th e th io cya n ic acid solution is added to an excess of p o ta s
sium perm anganate and th is excess is m easured b y another reagent. He also gives an a ltern ative pro
cedure for the determ ination of copper in w hich the cuprous hydroxide, obtained b y th e decom position of cuprous th iocyanate, is treated w ith a ferric salt and the reduced iron so form ed titra te d w ith perm an ganate as a measure of the copper. O b viously, this la st procedure wherein 1 C u = 1 F e w ould be less accurate in actual results, even th ou gh th eoretically correct, th an th e oxidation of th e th io cya n a te ion where 1 C u = 6 Fe, even th ou gh th e latter reaction is not s tric tly in accord w ith th e th eory. H ow ever, th e com bination of these tw o principles seems to g iv e a m ethod w hich p a rtly overcom es the defects of both.
T h is com bination of principles m ay be effected as follow s: P lace the filter paper containing th e cuprous th io cy a n a te in the beaker in which th e precip itation was m ade, add 25 cc. of hot 4 per cent sodium h ydroxide solution, and a gitate w ith a rod until the paper is shredded and the p recip itate decom posed. T h en add 25 cc. of cold 15 per cent sulfuric acid, 1 per cent ferric sulfate (anhydrous) solution. T h e result of this procedure w ith the volum es indicated gives a red m ixture of ferric th io cyan ate , ferrous sulfate, cupric sulfate, and a large proportion of cuprous th io cya n a te reform s when th e m ixture is acidified.
T h e principle of introducin g th io cya n ic acid into an excess of potassium perm anganate is now som ew hat approached in so far as only th a t portion of th e cuprous th io cy a n a te soluble in th e acid ferric su lfate is p re
sented for oxidation. T h e principle of th e oxidation of a ferrous ion for each cuprous ion is incorporated in th e reaction. T h e titra tio n proceeds read ily. A s th e end is approached the ferric th io cya n a te color gives w a y and th e m ixture becom es w h iter; 5 cc. of con cen trated hydrochloric acid should now be added to aid in th e solution of th e residual cuprous th io c y anate. F in ally, the solution is titra te d slo w ly to a stable perm anganate pink. T h e end color lasts about 3 min. Loss of color is p ro b ab ly caused b y the re
ducing action of the filter fibers or of th e hydrochloric acid.
T h e equation for th e reaction in this com bination procedure m ay be w ritten,
10 C u C N S + i4 K M n 0 4 + 2 iH 2S 0 4 =
C u S04 + 10 H C N + i 4 M n S04 + 7 K 2S 0 4 + i
6
H20
xo C u = i 4 K M n 0 4 = 70 Fe1 C u = 7 F e, or
C u : 7 F e = 63.57 : 390.88
whence, C u = 0.1626 Fe (Fe valu e of th e perm an
g an ate). T h u s the th eoretical valu e is reduced from 0.1897 to 0.1626. T h e actu al fa cto r m uch more n early approaches a linear coefficient and is ve ry m uch closer to its th eoretical value. Som e d ata to
1 S u tto n , " V o lu m e tric A n aly sis.”
Dec., 1919 T H E J O U R N A L OF 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 1 1 3 9 illu strate these points are herew ith given. Indefinite
am ounts of iron were used w ith each sam ple of copper.
T h e solution of K M n O ( (7 g. per 1.) on determ ination gave F e value of 1 cc. = 0.01207.
K M n O . A ctu al
C o p p er F o u n d U sing A v.
A ctu al C o p p er K M n O i G ra m C u R a tio , K V alue of K
N o. G ra m Cc. p e r Cc. C u : F e G ram
1 0 .0 1 3 8 7 .9 0.0 0 1 9 7 2 0 .1 6 3 4 0 .0 1 3 9
2 0 .0 2 7 6 13 .9 0 .0 0 1 9 8 5 0 .1 6 4 5 0 .0 2 7 6
3 0 .0 3 2 6 16 .4 0 .0 0 1 9 8 7 0.1 6 4 7 0 .0 3 2 6
4 0 .0 5 2 7 2 6 .5 0 .0 0 1 9 8 8 0.1 6 4 7 0 .0 5 2 6
5 0 .0 6 7 0 3 3 .9 0 .0 0 1 9 7 7 0.1 6 3 8 0 .0 6 7 4
6 0 .0 8 3 4 42 .1 0 .0 0 1 9 8 2 0.1 6 4 2 0 .0 8 3 6
7 0 .0 9 1 7 4 6 .1 0 .0 0 1 9 8 8 0 .1 6 4 7 0 .0 9 1 6
8 0 .1 2 1 4 6 1 .0 0 .0 0 1 9 9 0 0 .1 6 4 9 0 : i 2 1 2
9 0 .1 4 3 2 7 1 .9 0 .0 0 1 9 9 2 0.1651 0 .1 4 2 8
10 0 .1 6 2 5 8 1 .4 0 .0 0 1 9 9 6 0 .1 6 5 4 0 .1 6 1 7
11 0 .1 9 1 2 9 6 .2 0 .0 0 1 9 8 8 0 .1 6 4 7 0.1911
12 0 . 2 0 0 0 100.3
A v erag e =*0 .0 0 1 9 9 2
0 .0 0 1 9 8 6 0 .1 6 5 0
0 .1 6 4 6 0 .1 9 9 4
H ence, the actu al copper valu e of the perm anganate
= 0.01207 X 0.1646 = 0.001986 , thus the actual factor is 0.1646 and the theoretical 0.1626; the dif
ference is p rob ab ly due to the slight solubility of cuprous th io cyan ate.
S O M E O B S E R V A T IO N S O N T H E P R O C E D U R E
1— T h e stren gth of perm anganate solution, 7 g.
per 1., as used above, was selected because 10 cc. closely equals 1 per cent copper on a 2-g. sam ple of ore. This is a v e ry stron g solution, about three tim es th a t usually used for th e titratio n of iron, y e t 1 cc. equals only 0.1 per cent copper; hence it is v e ry easy to check to 0.02 per cent copper (on low -grade ores). Slight irregularities due to filter papers, etc., do not ap
p reciab ly affect th e results. H ow ever, the 5 cc.
concentrated hydrochloric acid should not be added to the liq uid being titrated until the end is nearly reached in order th a t enough m anganese sulfate m ay be present to act as acceptor betw een the ferrous iron and th e perm anganate.
2— T h e precipitation of the cuprous thiocyanate from ab out a 2 per cent sulfuric acid solution (other acids h a vin g been rem oved b y evaporation to sulfur trioxide fum es) has been found satisfactory. A solu
tion containing 4 per cent sodium th iocyanate and 10 per cent sodium sulfite is used as precipitating agen t (10 cc. of this usually suffices for most samples).
3— Unless the insoluble residue is ve ry white it is advisable to rem ove it b y filtration before precipitating the cuprous th iocyanate.
4— T h e solution containing the cuprous thiocyanate should be boiled to coagulate the precipitate. I t m ay then be read ily filtered on a coarse paper th at has re
ceived tw o or three sm all washes of a “ filler.” This filler is m ade b y agitatin g 1 g. of corn starch (cooking starch) w ith 1 1. of w ater. T h is is a m echanical filler and does not relieve one of the necessity of using a few drops of sulfuric acid in the hot w ater used to wash the precip itate to prevent form ation of a hydrosole.
5— T h is starch filler has been found to insure ve ry clear filtrates even when using coarse filter paper.
T h e am ount used has not been observed to consume any appreciable q u a n tity of perm anganate either b y itself or b y possible products of its hydrolysis under the conditions of the procedure.
6— T h e titratio n seems to be effected most accurately
in the solution volum es p reviou sly indicated. If larger am ounts of copper are being titrated it w ould be better to use stronger perm anganate.
S U M M A R Y
A m odification of the usual perm anganate m ethod for copper is presented w hereby (a) the theoretical ratio of copper to iron is reduced from 0.1897 t0 0.1626;
(b) the actual ratio factor is found to more closely approach th e character of a linear coefficient; (c) the procedure seems in m any cases to be more rapid and to give more accurate results.
Po t r e r il l o s La b o r a t o r ie s
POTRERILLOS, C lIIL E #
THE USE OF NICKEL CRUCIBLES FOR THE J. LAWRENCE SMITH FUSION IN DETERMINING SOIL POTASSIUM
B y Se t h S . Wa l k e r R eceiv ed J u ly 7,; 1919
T h e scarcity and high price of platinum during the war led the w riter to in vestigate the feasib ility of su b
stitu tin g nickel crucibles for platinum ones in fusing soils b y the J. Law rence Sm ith m ethod for to ta l potassium . There w ould seem to be no theoretical reasons against th e use of nickel for th is purpose.
Still, it is noticeable th a t w herever th e Sm ith fusion m ethod is described in the literature platinum cruci
bles are specified, and in view of this th e w riter did not feel justified in m aking the substitution w ithout experim ental proof of its adequacy.
A ccordin gly dup licate fusions were m ade on a num ber of soils, using a platinum crucible for one duplicate and a nickel crucible for th e other. In all cases 0.5 g. of dry soil was taken and th orough ly m ixed w ith 0.5 g. of am m onium chloride and 4 g. of calcium car
bonate b y grinding in an agate m ortar. T h e m ix
tures were fused (after the usual prelim inary heating to expel am m onia) for 45 min. a t the highest heat obtainable w ith a good Bunsen burner. T h e subse
quent operations were essentially as described b y Am es and G aith e r1 and were carried out alike for all determ inations. Porcelain dishes were used for th e final evaporation w ith platinum solution. T h e p o ta s
sium precipitates were collected on G ooch crucibles and dried in a w ater oven. T h e follow ing tab le shows the w eights of potassium chlorplatinate found b y the tw o methods.
We i g h t so f K jP tC le Fo u n db y Fu s in g So il si n Pl a t in u m a n di n Ni c k e l Cr u c i b l e s
Kin d o p Cr u c i b l e
P la tin u m N ick el
Soil. N o . G ra m G ra m
S-223 0 .0 1 4 2 0 .0 1 4 5
S-254 0 .0 0 8 0 0 .0 0 8 2
S-255 (0 .0 1 5 8 0 .0 1 7 8
1 0 .0 1 7 7 0 .0 1 7 5
S-258 0 .0 0 9 6 0 .0 0 9 8
S-259 0 .0 1 1 8 0 .0 1 1 8
S-260 0 .0 0 3 4 0 .0 0 3 2
S-262 0 .0 0 3 7 0 .0 0 3 8
D IS C U S S IO N O F R E S U L T S
In only one case, viz., Soil S-255, was there an a p preciable difference in th e w eights found; and when the com parison was repeated on th at soil, results were obtained which not only agreed betw een them selves, bu t also w ith the result p reviou sly obtained w ith the
1 Ohio A gr. E x p t. S ta tio n , B u lletin 261, 507.
T H E J O U R N A L O F 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 Vol. n , No. 12 nickel crucible. T h is indicates th a t the discrepancy
at first observed was due to som e un detected error in m anipulation w ith th e p latinu m crucible fusion, rath er th an to in ad eq u acy of the nickel crucible.
at first observed was due to som e un detected error in m anipulation w ith th e p latinu m crucible fusion, rath er th an to in ad eq u acy of the nickel crucible.