October 15, 1932
INDUSTRIAL AND ENGINEERING CHEMISTRY
397
ticles of dark-colored material will dissolve. No doubt arsine is also dissolved in the liquid in the flask, and this is liberated upon boiling. Sufficient standard iodine solution should be present in tubes C and D so that all of it is not reduced by the arsine, else unreliable results will be obtained. TABLE 1. ARSENIOUS OXIDEFOUND AND PRESENT BY IODOMETRIC AND ACIDIMETRIC METHODS
0.07 gram of arsenious oxide is passed into 100 cc. of 0.05 N solution of iodine. The determination should be arranged so that not more than this amount of arsenic is present if it is desired to titrate both the residual iodine and acid formed.
Cram
I I1 I11 IV V VI VI1 VI11 IX X XI XI1
0.02475 0,02475 0.02475 0.02475 0.02475 0.02475 0.02475 0.002475 0,04950 0.04950 0,04950 0.04950
Gram
LITERATURE CITED
AstOa BY ACIDIMETRIC METHOD Present Found Diff.
AszOa B Y IODOMETRIC METHOD S A X P L I Present Found Diff Gram
Gram
-0.00014 0.02461 +0.00005 0.02480 +0.00017 0.02492 +o .00002 0.02477 +o. a0017 0.02492 0.02480 + O . 00005 0.02476 0.00000 0.002596 +o. 00012 0.04941 -0.00009 $0.00029 0.04979 $0.00004 0.04954 + O . 00014 0.04964
0.02475 0.02475 0.02475 0.02475 0.02475 0.02475 0.02475 0.002475 0.04950 0.04950 0.04950 0.04950
Gram
(1) Ericsson, A,, Svensk Farm. Tid., 18, 473-8 (1914). (2) Lochman, R., 2. fisterr. Apoth. Vet-., 45, 744-5 (1907).
Gram
0.02475 0.00000 0.02493 $0.00018 0 , 0 2 4 5 8 -0,00017 0,02459 -0.00018 0.02464 -0.00011 0.02483 $0.00008 0.02464 -0.00011 0.00282 +O. 00033 0.04928 -0.00022 0.04948 -0.00002 0,04948 -0.00002 0.04928 -0.00022
RECEIVED June 23, 1932.
A Laboratory Extractor
H. G. TANNER, E. I. du Pont de Nemours & Co., Wilmington, Del. ARSEN-
TABLE11. RESULTS OBTAINEDBY PROCEDURE 1 WITH ATES AND ARSENITESPRESENT IN RECEIVINQ IODINE SOLUTION SAMPLE AsrOa PRESENT Gram
AmOr FOUND
DIFFERENCE
Cram
Gram
0.10019 0.09809 0.09840 0.09842 0.09809 0.08032 0.11976 0.09987
$0.00116 -0.00084 -0.00053 -0.00061 0.00084 +0.00032 -0.00024 -0.00013
-
When larger than the above-mentioned amounts of arsenic are present in the sample, the receiving iodine solution will contain both arsenate and arsenite. In such cases, the volume of iodine originally added and the amount used in back titration are added, and from this is subtracted the volume of thiosulfate used in titration The arsenic present is found by multiplying the difference by the proper factor. For example, suppose 120 cc. of 0.1 N iodine were used as the receiving solution and 30 cc. of 0.1 N thiosulfate were used to titrate the residual iodine, and also that 7 cc. of 0.1 N iodine were used to titrate back after neutralization. 0.1 N I, cc.
120 30
0 . 1 N Na&Oa, cc.
-
0 . I N I used in back titration, cc. 97 X 0.001237 = 0,119989 gram As1Oa present
90
-7 97
Tables I and I1 show results obtained.
COMMENTS Since in going from arsine to orthoarsenic acid arsenic changes 8 in valence, it is possible to determine very small quantities of arsenic in a volumetric way. It has been found practical to use 0.01 N solution of iodine, one cc. of which equals 0.0001237 gram of arsenious oxide. Since one can check. readily to about 0.2 cc., it has been found possible to determine quantities of arsenic as small as 0.00002 gram. The method herein described should be four times as sensitive as the ordinary titration of arsenic with iodine. The acidimetric titration is a valuable check on the accuracy of the iodometric titration. The work done shows that it is impossible to liberate all the arsenic from a sample as arsine without boiling. The boiling has gone far enough when the last particle of metal has been dissolved. Although the reaction of the acid on the material in the flask may have ceased before boiling, it will be found that when the contents of the flask are brought to boiling par-
T
HE accompanying photograph shows an extractor of considerable capacity which was constructed almost entirely by the assembly of common laboratory apparatus. Within a tall-form liter beaker was placed a glass tripod which was readily constructed of glass rod. A 35 by 70 mm. crystallizing dish rested in an inclined position on this tripod. A 15-cm.folded filter within this dish contained the mat e r i a l to be e x t r a c t e d . Suspended in the mouth of the beaker was a 250-cc. distilling flask which served as the condenser. The extractor is particularly well adapted to the purification of organic compounds. It r e s e m b l e s in some respects an extractor described in the literature ( I ) , wherein a large funnel is used to support the filter. It h a s n u m e r o u s a d vantages, however, over the “funnel” extractor. Comparative tests showed that it has a much higher speed of extraction; the solvent is c o n d e n s e d more effectively when boiled vigoro u s l y ; the drip from the c o n d e n s e r flask does not channel through the charge in the filter; “choking” of ascending vapor with condensate in the funnel stem is avoided; and contamination by m a t e r i a l f r o m stoppers does not occur. When used with 200 cc. of carbon tetrachloride as the extraction medium, no appreciable amount of solvent escaped during a 6-hour run. Decolorizing charcoal, intimately mixed with the material to be extracted prior to filling up the filter, frequently assisted purification, LITERATURE CITED (1) Conant, J. E., “Organic Syntheses,” Vol. 11. p. 49, 7’v ley, 1922. RECEIVED June 21, 1932. Contribution 102 from the Experimental Station, Nemours & Co
a. I. du Pont de
