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Solutions 1, 2, 3, etc., of each digested compound were then analyzed by the Gutzeit method until a dilution was reached which caused no visible interference with the results of analysis. In each case, 5-, lo-, and 15-cc. aliquots, corresponding to 10,20, and 30 micrograms of arsenic trioxide, were used. One set of analyses was made with stick zinc, and a second set was made with granulated zinc (20-mesh) at the rate of 2 grams per generator bottle. The results of analysis were calculated as percentage recovery of the total amount of arsenic present. The data showed that the percentage of arsenic recovered depends solely on the amount of interfering compound present, and is not influenced by the amount of arsenic contained by the aliquot, a t least not through the range of 10 to 30 micrograms. Figure 2 shows the average percentage of the total arsenic recovered in the presence of pyridine compounds ranging from 0 to 20 mg. digested per aliquot used. Granulated zinc (20-mesh) a t the rate of 2 grams per generator bottle was used in these analyses. It will be observed that y-y-dipyridyl exerts a tremendous degree of depression on the results of analysis, and that nicotine and pyridine produce a marked depression; whereas nicotinic acid, piperidine, and quinine cause much less interference. It would not be expected that quinine would have a great restraining influence, inasmuch as its one pyridine ring is only a small part of its total molecular structure. Figure 3 is based upon the results of analyses similar to those used for Figure 2, except that stick zinc was used for evolution purposes. It will be noted that with the exception of y-y-dipyridyl the results of analysis are distinctly higher when stick zinc instead of granular zinc is used. This same circumstance was noted previously in connection with the tobacco analyses shown in Figure 1. A comparison of the nicotine curves in Figures 1, 2, and 3 shows that much lower results were caused by nicotine during routine tobacco analysis than when the digestions were made with pure nicotine. This would indicate that the method of nicotine analysis does not detect all the interfering compounds present in tobacco.
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It may be mentioned here that the ability of pyridine compounds to cause these disturbed evolution conditions does not originate as a result of digestion with nitric and sulfuric acids. The pyridine compounds before digestion cause the same type of interference to an equal or a greater degree than they do after digestion. GENERALCONSIDERATIONS Aside from tobacco, not many products which are analyzed for arsenic are likely to contain pyridine or its derivatives in amounts sufficient to cause low results of analysis. Among the possibilities are materials containing animal hides, bones, or bone oil. It is possible also that apples sprayed late in the season with nicotine sulfate may contain nicotine residues sufficient to interfere with the determination of arsenical residues deposited during previous sprayings with lead arsenate. Unsuspected sources of pyridine interference may likewise be encountered at times in organic products of unknown origin or composition. When materials of this nature are being analyzed for arsenic, it would be advisable to observe closely the character of the evolution and, in case of any abnormal appearance, to verify the results by making analyses after phosphate precipitation. ACKNOWLEDGMENT The author wishes to express his appreciation for the assistance rendered by Julian Hiley in carrying on much of the analytical work connected with this investigation. LITERATURE CITED (1) Assoo. Official Agr. Chem., Official and Tentative Methods, pp, 109, 306-9 (1930). (2) Ibid., p. 203. (3) Ibid.,p. 308, section 4. RECEWED April 15, 1932. Presented before the Division of Agricultural and Food Chemistry at the 82nd Meeting of the American Chemical Society, Buffalo, N. Y., August 31 to September 4, 1931.
Analysis of White Metals and Their Smelter Products HANSNEUBERT, R. F. D. No. 1, Box 150-B,Rahway, N. J.
T
HE samples as delivered from the sample mill consist
mostly of a bar and slag which have to be weighed out in proportional parts. The metallic part, however, is generally not uniform, so that a larger sample has to be taken in order to get a good average. This difficulty obviously does not exist in the case of slags which are perfectly well miscible. The method of analysis as used in the laboratory of the U. S. Metals Refining Company begins differently from the methods generally used, which consist in a separation of the tin from the rest of the other metals by precipitating it as metastannic acid in nitric acid solution. This method of attacking the white metals with nitric acid has the undeniable disadvantage that the metastannic acid is never chemically pure, that a small part of the tin goes into solution, and that a very difficult operation ensues as soon as a greater weight of metal is taken for analysis. Therefore, experience has shown that it is preferable in any case to dissolve the metallic part to a clear solution in
hydrochloric acid, and take this solution as the starting point for further operation. The antimony and copper, which are attacked with difficulty by hydrochloric acid, are dissolved by an addition of sodium chlorate dissolved in water, or by a few drops of nitric acid. The oxidizing substance is chosen according to a preliminary test for copper. If this test shows that the copper is low, then the antimony and copper are oxidized with sodium chlorate so that a straight volumetric determination can be made later. The method used for the bar is as follows: The proportional part corresponding to 20 grams of the sample is dissolved in a 500-cc. flask with concentrated hydrochloric acid a t moderate heat, After the reaction ceases, the antimony and copper are dissolved by adding just enough oxidizing agent for the purpose. The flask is then cooled and filled up to the mark with concentrated hydrochloric acid, the contents are mixed, and the flask held in readiness for the slag part. If it is intended to run the tin by the straight volumetric
January 15, 1933
INDUSTRIAL AND ENGINEERING
method, it has to be attacked only by concentrated hydrochloric acid plus water a t boiling temperature, using sodium chlorate to dissolve the antimony. For the determination of lead, copper, and antimony, any suitable acid may be used. If the slag does not dissolve, i t has to be fused with sodium peroxide and treated according to the following procedure: TIN. One-half gram is weighed into a nickel crucible, fused with sodium peroxide, and the fusion decomposed with water in a 400-cc, beaker. To this fusion 12.5 cc., equal to 0.5 gram, are tapped from the 500-cc. flask. If a preliminary test shows the absence of copper in great quantities, the solution is neutralized with hydrochloric acid, and an excess of 80 cc. is added. This solution, which should be about 200 cc., is boiled for a few minutes to expel all chlorine, and is then ready to be reduced and titrated according to standard methods. If the preliminary test shows high copper, the procedure is somewhat different. To the clear solution of hydrochloric acid are added 10 to 15 cc. of ferric chloride solutions (500 grams of ferric chloride to 5000 cc. of water), then ammonium hydroxide in excess, and 3 to 5 grams of ammonium carbonate. This is boiled for a short time and filtered. After the copper is washed out, a hole is punched in the filter paper through which the precipitate is washed into a 500cc. Erlenmeyer flask. The adhering precipitate is cleaned from the filter paper by washing out with hydrochloric acid (1 to 1). (It is not necessary to wash out the copper quantitatively from the precipitate of the hydroxides, as copper in small quantities does not influence the titration of the tin.) Enough hydrochloric acid is then added to the solution to bring the total free acid up to 80 cc. It is then ready t o be run for tin according to standard methods. LEADAND COPPER. If the slag does not dissolve in acid, one gram of it is fused in an iron crucible with sodium peroxide. The fusion is decomposed with water in a 600-cc. beaker, 25 cc. (equal to one gram) are tapped from the solution of the metallic part, and 60 to 70 cc. of yellow sodium sulfide (2500 grams of sulfide crystals dissolved in 12 liters of water with enough sulfur added to make the solution deep yellow) added to separate the lead and copper from the tin and antimony. The solution is boiled moderately, filtered, and waEhed twice with sodium sulfide containing hot water. Then the filter paper plus the precipitate is brought back to the beaker, 25 cc. of concentrated sulfuric acid added, and the paper destroyed by addition of nitric acid. After strong fuming, water is added and the solution boiled until the ferric salts dissolve. The lead sulfate is separated from the solution by filtration, and the lead determined as chromate according to standard methods. I n the filtrate the copper is determined according to the potassium sulfocyanate method with subsequent electrolysis. ANTIMONY.Two grams of the slag are fused in an iron crucible. The fusion is decomposed with water, 50 cc. (equal to 2 grams) of the solution of the metallic part are added, and the alkaline solution saturated with 70 to 80 cc. of yellow sodium sulfide. This solution is transferred to a 500-cc. flask and, after cooling, 250 cc. (equal to one gram) are filtered through dry filter paper. These 250 cc. are acidified with 100 cc. of concentrated hydrochloric acid, the solution boiled down to 150 to 175 cc., then 30 cc. of concentrated hydrochloric acid added and the solution gassed for 20 to 30 minutes with hydrogen sulfide to remove the arsenic as arsenous sulfide. The subsequent filtration is best done through a filter paper which has previously been moistened with hydrochloric acid (1 to 1). After two washings with this hydrochloric acid, the filter is finally washed with hot water. To this filtrate 3 to 5 grams of sodium
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chlorate are added and the solution boiled down t o crystals. After cooling, 100 cc. of water are added and the solution shaken until it is clear. Then a few crystals of potassium iodide are added and the liberated iodine titrated with sodium thiosulfate. NOTES.If the lead content of the white metal products becomes very high, the solution has t o be made in a 1000-cc. flask in order t o keep the lead chloride from precipitating in the hydrochloric acid solution. In adding the oxidizing reagent, an excess of nitric acid must be avoided. If too much acid has been added and the lead chloride crystals begin to precipitate after cooling, the whole solution plus the precipitated lead chloride must be transferred to a bigger flask so that the greater quantity of hydrochloric acid can keep the lead chloride in solution. RECEIVED July 18, 1932.
Modified Combustion Apparatus R. N. EVANS Research Bureau, Brooklyn Edison Co., Inc., Brooklyn, N. Y.
S
EVERAL improvements in analytical combustion a p paratus have been recently published (1, S), one of which is the use of interchangeable ground-glass joints ( 2 ) . The chief difficulties in the latter design are the faulty alignment of the individual units which go to make up the train, the liquefaction of the grease on the ground joints of the combustion tube, and the delay and awkwardness in the process of inserting the boat containing the sample to be analyzed. The photograph illustrates the manner in which these difficulties were overcome in this laboratory. A circular flexible piece of glass tubing in the train allowed for expansion on heating and also compensated for lack of alignment. The side arm of the combustion tube made it possible to insert the sample without interrupting the flow of gas or without dis-
connecting the sections of the train. Finally, copper radiating vanes were fitted to the quartz tube by first winding the tube with fine copper wire and then soldering the copper collar, with the attached radiating fins, to the layer of copper wire. Ordinary stopcock grease was used with no difficulty when the joints were protected from the thermal flow in this manner. LITERATURE CITED (1) Avery and Hayman, IND.ENG.CHEM.,Anal. Ed., 2, 336 (1930). (2) Brunn, J., Bur. Standards J. Research, 2,487 (1929). (3) Stanffeld and Sutherland, Can. J . Research, 3, 318-21 (1930). RECEIVEDSeptemher 20, 1932
