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Vol. 13, No. 2
INDUSTRIAL AND ENGINEERING CHEMISTRY
in their average precision-one of those in the British Pharmacopoeia has limits Of 92 to logper cent (Staphylococcus antitoxin), another limits of 37 to 272 per cent (vitamin A)but the precision of the assay of a single drug varies from laboratory to laboratory and from one run to another in the same laboratory. No assay with a n indeterminate error can be considered satisfactory.
Literature Cited Bliss, C. I., Ann. Applied Biol., 22, 134-67 (1935). Bliss, C. I., J . Am. Statistical Assoc., 35, 498-506 (1940). Bliss, C. I., and Hanson, J. C., J . Am. Pharm. Assoc., 28, 521-30 (1939).
Bliss, C. I., and Marks, H. P.,Quart. J. Pharm. Pharmacol., 12, 82-110, 182-205 (1939).
(5) Bliss, C. I., and Rose, C. L., Am. J . Hug., 31, See. A, 79-98 (1940). (6) British pharmacopeia Committee, 10th Rept. of SubCommittee on Accuracy of Biological Assays, General Medical Council, London, 1936. (7) Gaddum, J. H., Medical Research Council (Brit.) Special Rept. 183, H. M. Stationery Office, London, 1933. (8) Gold, H., Kwit, N. T., and Cattell, McK., J . Pharmacol., 69, 177-97 (1940). (9) Miller, L. 'C., Bliss, C. I., and Braun, H. A., J. Am. Pharm. ASSOC., 28, 644-57 (1939). (10) Morrell, C . A., Chapman, C. W., and Allmark, M. G., J . Pharmacol., 64, 14-42 (1938).
PRESENTED before the Division of Medicinal Chemistry, Symposium on Methods for the Standardization of Drugs, at the 100th Meeting of the American Chemical Society, Detroit, Mich.
Determination of Silicon In Monel Metal, Copper-Silicon Alloys, and Similar Nonferrous Alloys Containing Silicon FREDERICK B. CLARDY, HERMAN R. hIAUPITY, AND R. STEVENS GIBBS Chemical Laboratory, U n i t e d S t a t e s Navy Yard, P o r t s m o u t h , Va.
I
N THE determination of silicon in Monel metal, copper-
silicon alloys, and similar nonferrous alloys containing silicon, a rapid, accurate method, to replace the longer and more commonly used methods of dehydration by nitric-sulfuric acids or hydrochloric acid and potassium chlorate, is needed for the analysis of a large number of samples. Little attention appears to have been paid to the use of perchloric acid for the dehydration of silica in these materials. V7illard and Cake (2) proposed the use of perchloric acid as a dehydrating agent in silicon determination. Both they and Fowler (1) have pointed out the disadvantages of nitric, sulfuric, and hydrochloric acids in the dehydration of silica in steels, silicates, and some other metals and alloys. These same disadvantages (slow evaporation, slow solution of soluble salts, bumping and spattering of the solution, and the necessity of recovering silica from filtrates) apply to Monel metal and other nonferrous alloys containing silicon. The following procedure, evolved by this laboratory gives accurate results in from 2 to 3 hours, eliminates the disadvantages of the nitric-sulfuric acid and hydrochloric acid procedures mentioned above, and avoids the bumping that occurs when the metal is first dissolved in nitric acid and then fumed with perchloric acid.
num crucible, ignite, cool, and weigh. Volatilize silica with hydrofluoric acid plus 3 drops of sulfuric acid, ignite again, cool, and reweigh. The loss in weight is silica (SiOz). The residue remaining in the crucible will consist of traces of nickel, iron, and titanium. This can be fused with pyrosulfate, dissolved in water, and added to the filtrate. Some platinum will be introduced during this fusion and will be subsequently deposited with the copper and weighed as such. This has been found to be extremely small and in routine analysis can be disregarded. The filtrate from the silicon determination can be used for the determination of copper, iron, and titanium by the following procedure : Boil filtrate strongly to remove free chlorine, and add 1 ml. of concentrated nitric acid and 5 ml. of concentrated sulfuric acid. Keep the volume of solution a t approximately 300 ml. Electroplate copper on the platinum cathode at 0.5 ampere and 3 volts. After copper is removed, make the solution weakly ammoniacal and determine iron and titanium in the usual manner. Excess ammonia will form a precipitate with perchloric acid. Table I gives results by the three methods for determining silicon in samples of blonel metal. I n each instance the filtrates were evaporated to dryness tn-ice to recover silica. No silica was found in the filtrates from the perchloric-nitric acid treatment. I n the other two cases sufficient silica was found to make these evaporations necessary.
Procedure for Monels Weigh 2 grams of fine drillings into a 400-ml. Pyrex beaker, add 25 ml. of 70 per cent perchloric acid and 1 ml. of concentrated nitric acid, place the beaker on a hot plate, and heat until solution of metal is complete. Add a few more drops of nitric acid if necessary to ensure complete solution. Place the beaker on an extremely hot electric or gas plate and boil the solution for about 10 minutes to ensure the complete dehydration of silica. The beaker may be heated over an open gas flame towards the end of this period and the contents of the beaker slowly revolved. Cool slightly, add water, and heat until all soluble salts are dissolved, boiling the solution at the end. Filter hot through a Whatman No. 41H or similar filter paper. Wash 5 times alternately with a solution containing a mixture of 1 per cent nitric acid and 1 per cent hydrogen peroxide, and with boiling water. Remove filtrate for the subsequent determination of other elements and wash the silica residue with hot 10 per cent hydrochloric acid and boiling water alternately 5 times and then with water until free from acid. Place filter paper in a 30-ml. plati-
TABLE I. DETERMINATIOS OF SILICON PerchloricNitric Acid Sample 1 Sample 2 Sample 3
Sulfuric; Nitric Acid
Hydrochloric Acid-Potassium Chloride
%
%
%
3.02-3.03 1.49-1.49 3.0s-3.09
2.99-3.01 1.50-1.46 3.04-3.19
3.07-3.10 1.48-1.46 3.08-3.12
Literature Cited (1) (2)
Fowler, R. M,,IND.EKG.CHEN.,Anal. Ed., 4, 382 (1932). Willard, H. H., and Cake, W. E., J . Am. Chem. SOC.,42, 2208 (1920).
THEviews presented in this article are those of the writers and should not be construed as the official views of the Navy Department.
