168
ANALYTICAL EDITION
thus with decreasing particle size the percentage of voids becomes smaller. The void content of the argillaceous silica decreases with increase of particle size. The finer fractions of this powder contain chiefly the softer clay; the coarser, the harder silica particles; and the intermediate fractions, mixtures of the two materials. The differences in void contents of the various fractions of this powder are probably due to the varying amounts of the two minerals composing them. The curves for marble, silica, limestone, and slate approach horizontal straight lines, indicating that for these materials particle size has no appreciable effect on void content. For trap rock and soapstone the curves indicate a higher void content for the finer fractions. The higher values are believed to be due to experimental difficulties encountered and not to increased void content associated with small particle size. With proper precautions the values obtained for the void content of the smaller fractions by the briquetting method show better agreement than those obtained by dry compaction or from liquid absorption data. The void contents of the powders exclusive of tripoli and argillaceous silica decrease from slate to limestone. Since fractions of about the same size distribution are compared, the differences in void content of these powders may be attributed to differences in particle shape and texture. It was
Vol. 5, No. 3
noticed on examining the powders under the microscope that, as the experimentally determined void content decreased, the particles became in general more regular and uniform in shape. LITERATURE CITED (1) Barnard, K. II., Paint,Oil Chem. Rev, 7 0 , s (1920). (2) Bartell, F. E., and Creager, 0. H., IND. ENB.C H ~ M21,1248-51 ., (1929). (3) Bartell, F. E., and Hershberger, A., Ibid., 22, 1304-9 (1930). (4) Gardner, H. A., and Coleman, R. E., Paint Mfrs. Assoc., U. S., Tech. Circ. 85 (1920). (5) Hougen, 0. A., and Hentzen, H. D., Chem. & Met. Eng., 29, 840-1 (1923). (6) Klumpp, E., Parben-Ztg., 32, 2306-7 (1927). (7) Klumpp, E., Kolloid-Z., 55, 348-51 (1931). (8) Manegold, E., Hofman, R., and Solf, K., Ibid., 56, 142-59 (1931). (9) Ibid., 57,23-39 (1931). (10) Marshall, C. E., J. Soc. Chem. Ind., 50, 444-50T (1931). (11) Norton, F. H., and Hodgdon, F. B., J. Am. Ceram. Soc., 15, 191-235 (1932). (12) Roller, P. S., Bureau of Mines, Tech. Paper 490 (1981). (13) Roller, P. S.,IND.ENQ.CHEM.,22, 1206-8 (1930). (14) Steiner, D., Zement, 21, 230-3 (1932). (15) WeBtman, A. E. R., and Hugill, H. R., J. Am. Ceram. SOC., 13, 767-79 (1930).
RECEIVED November 29, 1932.
A Modification of Bettendorff’s Arsenic Test With Adaptation for Mercury Determination W. BERNARD KINGAND F. E. BROWN,Chemistry Department, Iowa State College, Ames, Iowa The presence of mercuric chloride affects Betten- presence of mercuric chloride Bettendorfs test will dorff’s test for arsenic. The addition of enough detect a smaller quantity of arsenic than Gutzeit’s mercuric chloride to make its concentration 0.00001 test or Marsh’s test. The rate of formation of the M , before the addition of stannous chloride hastens colloidal arsenic is a function of the concentrathe appearance of the coloration, increases the sen- tion of mercuric chloride. Because of this, unsitivity of Bettendorff’s test ten to one hundred known concentrations of mercuric chloride as small fold, and enables the test to be made in a lower as 0.00000002 M m a y be determined by comparing concentration of hydrochloric acid. Mercuric chlo- the rate of appearance of color in the unknown soride in 0.00001 M solutions does not produce tur- lutions with the rate of appearance in the presence bidity when stannous chloride is added. I n the of known concentrations of mercuric chloride. HEN an excess of stannous chloride is added to a solution of a mercuric salt, a precipitate forms immediately. When an excess of stannous chloride is added to a solution of an arsenic compound in a high concentration of hydrochloric acid, a brown colloidal suspension of arsenic appears. If the concentration of arsenic is sufficiently great the suspension changes to a black precipitate. Frequently several minutes elapse between the addition of the stannous chloride and the appearance of the color due to arsenic. The delay in the appearance of the color is greater if the arsenic has been oxidized, as when arsenic sulfide is dissolved in hydrochloric acid and potassium chlorate. The greater delay persists even after the solution has been boiled to decompose the potassium chlorate. These facts seemed to indicate the possibility of testing for the presence of both mercuric compounds and arsenic compounds in the same solution by one addition of stannous chloride, if the precipitated mercury was filtered out immediately and the appearance of the coloration observed in the filtrate.
When an excess of stannous chloride was added to a solution containing compounds of both mercury and arsenic and the precipitate was removed as quickly as possible, no subsequent coloration of the filtrate appeared. It was evident that this procedure was useless as a simultaneous test for mercury and arsenic. However, very small amounts of a compound of mercury might hasten the appearance of the coloration due to arsenic in Bettendorff’s test and be useful in shortening the time required for that test, or for increasing its sensitivity. The amount of mercury compound added to a solution to be tested for arsenic by Bettendorff’s test must not be great enough to produce a turbidity due to the precipitated mercury. MODIFICATION OF BETTENDORFF’S TEST The experimental work on the modification of Bettendorff’s test consisted in determining the maximum concentration of mercuric chloride which will not produce turbidity when stannous chloride is added, and the effect of this concentra-
INDUSTRIAL AND ENGINEERING CHEMISTRY
May 15,1933
tion of mercuric chloride on the time of appearance of a coloration: (1) in cold solutions of varying concentrations of arsenic, (2) in solutions of arsenic in varying concentrations of acid, (3) in solutions of arsenic which had been boiled with potassium chlorate and hydrochloric acid, and (4) in solutions of arsenic which had been boiled with potassium chloride.
REAGENTS AND PROCEDURE The solutions of mercuric chloride and arsenic trioxide were prepared by diluting 0.1 M stock solutions in volumetric apparatus. The c. P. arsenic trioxide, mercuric chloride, and hydrochloric acid as furnished by reputable manufacturers were used without purification for the making of stock solutions. For all series of experiments except the one in which the concentration of the acid was varied, all solutions were made in, and all dilutions were made by means of concentrated hydrochloric acid. A very nearly saturated solution of stannous chloride was prepared by dissolving 453 grams of SnClz.2Hz0 in 250 cc. of hot concentrated hydrochloric acid. After cooling, strips of metallic tin were added to prevent oxidation. Each test was made with 10 cc. of solution prepared as follows: (1) the required amounts of mercuric chloride solution and arsenic trioxide solution were pipetted into a test tube, ( 2 ) concentrated hydrochloric acid to make a volume of 9.5 cc. was added, and finally (3) 0.5 cc. of stannous chloride solution was added and the contents of the tube were thoroughly mixed. The time a t which the stannous chloride was added was noted.
EXPERIMENTAL RESULTS I n the first set of experiments only mercuric chloride and stannous chloride were used. Table I shows the effect of 0.5 cc. of an approximately saturated solution of stannous chloride in 10.0 cc. of a solution of mercuric chloride varying in concentration from 0.001 M to 0.00001 M . CHLORIDE TABLEI. EFFECTOF ADDINGSTANNOUS MOLAR CONCN. OF HgClz 0.001 0.0005 0.0001 0.00005 0.00004 0.000025 0,00002
0.00001
TIMEELAPSINQ BETWEEN ADDITION O F STANNOTIS . ... CHLORIDE AND APPEARANCE OF: White Gray Maximum cloudiness oolor Opacity darkening Sec. Seo. Sec. Min. 10 15 20 1 10 15 35 1 15 1 min. 1 20 20 sec. 30 .. .. 30 sec. 1 min. .. 1 2.5 min. .. .. 2.5 (very faint)
....
..
..
..
..
These data indicate that more than 0.00001 mole, or more than 2 mg. per liter, or more than 2 parts per million of mercury must be present to produce a visible turbidity when an excess of stannous chloride is added under the conditions of these experiments. Table I1 presents a comparison of the times required for the appearance of the color in Bettendorff's test in the absence of mercuric chloride, and for the same test in the presence of 0.00001 M solutions of mercuric chloride, when the concentration of the arsenic trioxide was varied from 0.0005 M to 0.0000001 M . All tests reported in Table I1 were made at room temperature. The presence of a trace of mercuric chloride so small that the mercury does not form a cloudiness visible to the unaided eye leads to a formation of a n immediate brown coloration in a solution in which 10 minutes are required in the absence of the mercuric chloride. Besides, the sensitivity of the test is increased until only one-hundredth the concentration required for the uninduced test is required for the test when
169
mercuric chloride is present. One ten-millionth mole of arsenic trioxide per liter represents 0.00015 mg. of arsenic in the 10 cc. observed in the test tube. Ten times this amount, 0.0015 mg. of arsenic, shows its presence in 20 seconds if mercuric chloride is present. The sensitivity of the induced Bettendorff test equals or exceeds that of the Gutzeit (2) or Marsh test ( I ) . No stain for comparative purposes in the Gutzeit tests is recommended by Blyth for less than 0.002 mg. of arsenic. No standard mirror for the Marsh test is shown by Blyth for any amount of arsenic between 0.001 mg. and no arsenic whatever. An investigation will be made in this laboratory to learn whether the determination can be made quantitative by a comparison of intensities of color. T A B L11. ~ TIMEREWIREDFOR APPEARANCEOF COLORIN COLDSOLUTION (0.5 00. of saturated SnCle added)
TIMEELAPSINQ BETWBEN ADDITION OF SnClz APPEARANCE O F BROWN COLOR IN COLD SOLUTIONB ASrOa in concd. HCl AS203 in concd. HC1 CONCN.OF As208 and 0,OOOQlM HgClz Mole/E. Min. Min. 0 . OOOb 2.0 Immediately 0.0001 Immediately 4.5 0.00005 5.0 Immediately 0. on004 Immediately 5.0 0.00002 Immediately 10.0 0.00001' 10.0 Immediately (faint) 0.000001 .. 0.3 .. 0.0000005 0.5 .. 1.0 0.0000001 'In a review of the modifications of Bettendorff's test, Muhe (7) states that 0.0015 mg. of ar'8enic may be detected by the most favorable modification. In 10 CC. of a 0.00001 M solution of AszOs there are 0.016 mg. of aruenio. AND
The ordinary scheme of qualitative analysis separates tin and antimony sulfides from arsenic sulfide by means of concentrated hydrochloric acid, and subsequently dissolves the arsenic sulfide in concentrated hydrochloric acid with the aid of potassium chlorate. There is some doubt whether arsenic pentachloride (6) forms, but whenever the arsenic is dissolved in this manner the excess chlorine must be driven out by boiling before the stannous chloride is added. After the boiling, the appearance of the brown color is delayed, Since the delay might be due to the presence of the potassium chloride formed, similar experiments in which an equivalent amount of potassium chloride was added were made. Table I11 shows the results of these experiments. The times recorded are not comparable with those in Table 11, for the experiments on which Table I11 is based were made on hot solutions while those on which Table I1 are based were made on cold solutions. TaBLE 111. TIMEREQUIRED FOR APPEARANCE OF BROWN COLORIN HOTSOLUTION (0.5cc. of saturated SnCla added) TIMEELAPSINQB ~ T W E E N ADDITION OF SnCh AND APPIUARANCE OF BROWN COLORIN 10 cc. OF HOTSOLUTIONS CONTAININQ: 0.1 gram 0 1 ram 0.06 ram KClOa and CONCN. OF AsrOa K81os K8l 0.00001 M HgClp Mole/l. Sec. See. Sec. 0.00001 120 60 40 0.00002 90 45 22
The data of Table I11 show that the presence of traces of mercuric chloride hastens the appearance of the brown color due to arsenic even after it has been boiled with an oxidizing agent, and that the presence of the oxidizing agent contributes to the delay, since potassium chlorate produces a greater delay than an equivalent amount of potassium chloride. This delay due to boiling with the oxidizing agent might be caused by: (1) the presence of free chlorine not removed%byboiling, (2) the loss of arsenic chloride during boiling, (3) the loss of hydrogen chloride during boiling, or
ANALYTICAL EDITION
170
Vol. 5, No. 3
TABLE IV. CONCENTRATION OF REAGENTS AND TIMEREQUIRED FOR COLLOIDAL ARSENICSUSPENSION TO BECOME DENSER THAN STANDARDS A AND B MERCURIC CHLORIDE Conoentration of standard
x 10-6 x 10-6 x 10-6 x 10-6 1 x 10-6 1 x 101 x 10-6 1 x 10-6 1 x 10-6 1 x 10-6 1 x 101 x 10-6 1 x 10-6 1 x 10-6 1 x 10-1 1 x 101 x 101 1 1 1
cc.
FINAL ARSEINIC CONOINTRATZONTRIOXIDE x 108 1 X 10-3 M
cc.
45 40 35 30 25 20 15 10 9 8 7 6 5 4 3 2 1
HYDROCHLORIC STANNOUB ACID CHLORIDE Conoentrated Saturated
.
CC.
CC
0.5 6.5 10.5 15.5 20.5 25.6 30.5 35.5 36.5 37.5 38.5 39.5 40.5 41.5 42.5 43.5 44.5
2.5 2.5 2.5 2.5 2.6 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.6 2.5
(4) the presence of arsenic pentachloride. An attempt to determine which of these causes is effective is being made. Bettendorff's test requires a high concentration of acid. It seemed possible that a lower concentration of acid might be effective in the presence of the mercuric chloride than in its absence. Tests showed that Bettendorff's test made in the absence of mercuric chloride would detect the arsenic in 10 cc. of 0.00045 M arsenic trioxide when the concentration of hydrochloric acid is 6 MI or in 10 cc. of 0.001 M arsenic trioxide when the concentration of the hydrochloric acid is 5.4 M . If the concentration of the arsenic trioxide is 0.001 M and that of mercuric chloride is 0.00001 M , a brown color is produced in concentrations of hydrochloric acid as low as 3.0 M .
DETERMINATION OF MERCURY At the suggestion of H. H. Willard the authors attempted to determine mercury by observing the effect of the concentration of mercuric chloride on the time required for the reduction of the arsenic trioxide. This method for esti-
FIGURE1. DETERMINATION OF MERCURY
mating the concentration of an inductor has been reported by Feigl and Krumholn (d), who determined bismuth by its inductive effect on the reduction of lead salts by sodium stannite; by Feigl (S), who determined silver by its inductive effect on the reduction of mercury salts by phenylhydrazine; and by Hahn ( 5 ) , who determined silver by its inductive effect on the reduction of mercury salts by hypophosphites. Investigation showed that the concentration of mercuric chloride affected the rate of formation of colloidal arsenic in a Bettendorff test in which all other factors are kept constant.
TIMEREQUIRED -AMin. 2 2 3 3 3 4 6 6 7 8 8 9 10 11 12 14 17
-BSec.
22 52 19 31 54 57 6 46 25 15 51 28 9 0 7 5 0
Min.
4 6 6
6 7 8 9 12 13 14 14 15 16 17 20 22 27
Xec. 40 17 10 39 31 39 58
11 12 10 56 44 40 39 2 10 10
At first, an attempt was made to determine the time required for complete reduction of 0.00002 M arsenic trioxide by a saturated solution of stannous chloride in the presence of varying concentrations of mercuric chloride. The time required for complete reduction increases as the concentration of mercuric chloride decreases, but the point at which reduction is complete could not be observed with as high accuracy as was desired. The time a t which a changing suspension becomes definitely denser than an unchanging standard is more easily determined than the time a t which reduction is complete. Since the unchanging standard must be less dense than the completely reduced experimental sample, more than one standard may be used, and thus a reading on any experimental sample may be checked at any later stage of its reduction by comparison with a standard more dense than the first standard suspension. The data reported in this section were secured by viewing from above 50 cc. each of suspensions contained in matched Nessler tubes standing in a rack above an inclined white porcelain slab exposed to light from the northern sky. Two comparison tubes, A and B, were employed. The procedure was as follows: 1. Standard solutions of all substances to be used and a supply of concentrated hydrochloric acid were provided. 2. The two comparison suspensions were pre ared by adding 2.5 cc. of a saturated solution of stannous chyoride to mixed solutions of such com osition that when 2.5 cc. of a saturated solution of stannous cfdoride were added the resultant solution would be 50 cc. of solution 0.00001 M with respect to arsenic trioxide and 0.000002 M with respect to mercuric chloride for A, and 0.00002 M with respect to arsenic trioxide and 0.000002 M with respect to mercuric chloride for B. These solutions are completely reduced in a few minutes and the suspensions do not change in appearance for several hours. 3. The experimental tubes were prepared so that a 50-cc. sample of solution would be 0.00004 M with respect to arsenic trioxide (twice the concentration of the more concentrated standard) and from 0.0000009 M t o 0.00000002 M with respect to mercuric chloride in different tubes, when 2.5 cc. of saturated stannous chloride were added. 4. Stannous chIoride was measured into each of the experimental tubes from a buret and the time at which the addition was complete was noted for each tube. The contents of the tube were quickly mixed by stoppering and inverting. 5. Each experimental tube was laced in the rack near comparison tube A and the time wien it became definitely darker than A was recorded. 6. The tube was then placed near oom arison tube B and the time when it became definitely darker tfan B was recorded. The data are recorded in Table IV and are represented by the curves in Figure 1. After the standard solutions were prepared, two persons (one preparing and comparing suspensions and the other recording data and making calculations) spent about 1.5 hours in collecting the data. Since temperature, Concentration of acid, concentration of arsenic trioxide, boiling with oxidizing agents, and the I
May 15, 1933
INDUSTRIAL AND ENGINEERING
concentration of stannous chloride if it is small are known to affect the rate of formation of the suspension, the time concentration curve should be determined by each analyst for the conditions under which he will make his determinations. No substances were found to interfere with this determination except the noble metals such as gold and platinum which form colloids and obscure in whole or in part the colloidal arsenic. SUMMARY
1. When an excess of stannous chloride is added to mercuric chloride dissolved in concentrated hydrochloric acid, no cloudiness appears if the concentration of the mercuric chloride is as low as 0,00001 M . 2. Bettendorff’s test made in the absence of mercuric chloride will detect the arsenic in 10 cc. of 0.00001 M arsenic trioxide dissolved in concentrated hydrochloric acid. The faint brown color appears in about 10 minutes. 3. When, in addition to saturated stannous chloride, enough mercuric chloride to produce a concentration of 0.00001 M is added to solutions of arsenic trioxide in concentrated hydrochloric acid, colorations appear immediately when concentrations of arsenic trioxide are as low as 0.00001 M and in one minute with concentrations as small as 0.0000001 M with respect to arsenic trioxide.
CHEMISTRY
171
4. The presence of mercuric chloride hastens the appearance of the coloration due to arsenic in Bettendorff’s test after boiling with potassium chlorate. 5. The presence of mercuric chloride reduces the concentration of hydrochloric acid required for Bettendoxff’s test from more than 5 M to 3 M when the concentration of arsenic trioxide is 0.001 M . 6. The time required for the appearance and development of the arsenic suspension is a function of the concentration of mercuric chloride in the solution. This behavior may be used to determine the concentrations of mercuric chloride in concentrations as low as 0.00000002 M . 7. The preferred procedure is to compare the increasing depth of color in experimental suspensions to prepared standards. Several comparisons may be made. LITERATURE CITED (1) Blyth and Cox, “Foods and Their Composition and Analysis,” 7th ed., p. 439, Charles Griffin & Co., London, 1927. (2) Ibid., p. 442, Figure 78. (3) Feigl, Mikrochem., 10,305 (1931). (4) Feigl and Krumholz, Ber., 62, 1138 (1929). (5) Hahn, Ibid., 65, 840 (1932).
(6) Mellor, “Comprehensive Treatise on Inorganic and Theoretical Chemistry,” Vol. IX, p. 241, Longmans, 1929. (7) Muhe, H., 2. anal. Chem., 55, 359-63 (1916). RBCEIVED September 14, 1932.
Loading Combustion Tube in Carbon and Hydrogen Determination on Liquids J. R. BAILEY,Chemical Laboratory, University of Texas, Austin, Texas
I
N CONNECTION with research on petroleum bases, involving many analyses of liquid samples for carbon and hydrogen, the direct introduction of the sample into the combistion tube from a pipet has proved more satisfactory than the use of a boat or a glass bulb. A standard weighing pipet (Figure 1) of 2.5 cc. capacity is employed, and, to avoid trapping air a t the delivery end of the pipet, a capillary hole- A- is drilled through the mantle below its ground-glass connection. I n loading the combustion tube, a removable layer of copper oxide, constituting about half of the charge, is transferred to a Thiele reservoir of 100 cc. capacity, and then the tube is secured in a rigid vertical position in a stand (Figure 2) which carries a projecting plate a t the lower end, with a cup B for insertion of the tube and a hinged clasp C above for keeping it plumb. A brass pipet holder is attached to the combustion tube a t D; the pipet, held a t the stopcock with the index finger and thumb of one hand, is withdrawn from its mantle and the projecting end above the bulb is inserted through a circular hole (slightly inclined) in the guide plate F , far enough to allow the outlet end to pass into a slit leading to the conical seat E. On release of the pipet, the bulb is adjusted to its conical support and the pipet is centered automatically just above the FIGURE1
combustion tube in such alignment that, on introduction of the sample, every drop descends to the permanent layer of copper o x i d e , without i m p i n g i n g along the sides of the combustion tube. The pipet can be quickly returned to the mantle for weighing and after the pipet holder is detached the Thiele reservoir is placed over the combustion tube and copper oxide s h a k e n in above the sample. This procedure in analysis of liquids of low volatility insures complete comb u s t i o n and reduces to a minimum the danger of a mishap in m a n i p u l a t i o n , which might result in loss or contamination of sample. e
ACKNOWLEDGMENT Credit is due W. L. Benson , m e c h a n i c i a n in this laboratory, for construction of the metal equipment described in this paper. IGURE
2
RECEIVBD February 17, 19aa.
