APRIL 13, 1938
\\iLlTIO\L
allowed to digest for 30 minutes at about 75' C. The precipitates were collected in veighed platinum Gooch crucibles with asbestos beds, washed five t o six times I=,-ith hot (70" C.) distilled water, and dried a t 110" C. for 1 hour. The factor 0.2032 was used to convert the weight of nickel dimethylglyoxime to nickel. The ayerage of five closely agreeing results gave a value of 29.82 per cent of nickel in the 30 per cent nickel steel. When a n alcoholic solution of the dimethylglyoxime was substituted for the sodium hydroxide solution in the method just described, an average of two determinations gave 29.70 per cent of nickel. According to Lundell, Hoffman, and Bright ( 5 ) , alcohol has a greater solubility effect than ammonium hydroxide, ammonium salts, or alkali acetate. The difference between the electrolytic and the dimethylglyoxime value is large compared to the close agreement obtained by the cyanide method based on pure nickel. The following experiments were made to determine whether the difference could be due entirely t'o the solubility of the nickel dimethylglyoxime. One-gram samples of the 30 per cent nickel steel were dissolved in nitric acid, diluted to 1 liter, and divided into ten portions. The nickel in all ten portions n-as precipitated with dimethylglyoxime (sodium hydroxide reagent), filtered, washed, and run in all respects under the same conditions as the original dimethylglyoxime standardization. The precipitates were discarded and the filtrates evaporated to dryness. The citric acid, the excess reagent, and the ammonium salts were destroyed by oxidation with nitric and perchloric acids. The portions were combined and the remaining nickel was again precipitated in a small volume with dimethylglyoxime. An average of tm-o such runs gave a result of 0.12 per cent of nickel, t o which 0.01 per cent should be added to allow for the h a 1 solubility. This corrected value (29.82 0.13 = 29.95) is in very good agreement with both the electrolytic and t'he cyanide values. A number of other cases seem worthy of reporting. A sample of Invar was found to contain 35.90 per cent of nickel by cyanide titration, based on pure nickel. The dimethylglyoxime method, using 0.1-gram samples (aliquoted from 1-gram samples), showed 35.62 per cent of nickel. In another case, an iron-nickel alloy was found t o contain 41.34 per cent of nickel by cyanide titration, based on pure nickel. The dimethylglyoxime method, using 0.08-gram samples (aliquoted from 1.6-gram samples), showed 40.99 per cent of nickel. An alloy of the 80 per cent nickel-20 per cent chromium type was analyzed for nickel by cyanide titration, using accurately weighed 0.4-gram samples, the cyanide solution being sbandardized against ure nickel. An average of 77.2 per cent of nickel was foun2 An average of 77.1 per cent of nickel was found by standardizing against 1-gram portions of the 30 per cent nickel steel (29.96 per cent of nickel). The dimethylglyoxime method, using 0.04-gram samples (aliquoted from 0.4gram samples), gave a value of 76.7 per cent of nickel.
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EDITIOh
179
A determination of nickel by the recommended procedure in Sational Bureau of Standards 18 Cr-8 Ni steel 101 gave an average value of 8.49 per cent of nickel, after correcting for copper and cobalt. (Cobalt is not listpd on i h e certificate, but this laboratory obtained a value of 0.058 per cent. The certificate yalue for copper is 0.055 per cent.) The cyanide solution was standardized on a synthetic mixturc: of 0.2800 gram of the nickel steel ( S i = 29.96), 0.175 gram of chromium ( C r I I I ) , and 0.5 gram of Sational Bureau of Standards open hearth iron 55a. The certificate value of 8.44 per cent of nickel for this standard may be slightly low, since the dimethylglyoxime met,hodwas used by most of the cooperators listed on the certificate of analysis.
Conclusions
A photometric apparatus has been developed to detect the end point in the cyanide titration method for nickel and found to be greatly superior to the eye, particularly in analyses of high-chromium alloys. It is possible to run duplicate determinations in 35 to 40 minutes on iron-nickel alloys. High-chromium alloys necessarily require more time because of the difficulty of dissolving such samples. The accuracv t h a t can be expected is of the order of 0.1 per cent. The solubility of nickel tiiinethylglyo?time is demonstrated and it is shown that less dependence should be placed on this method when applied t o high-nickel steels where the highest order of accuracy is desired.
-4cknowledgment The author wishes to thank C. Sterling and W.A. Wesley of the International Sickel Company for the pure nickel used in this work. H e wishes also to thank the officers of the Carpenter Steel Company for their encouragement during the progress of this work.
Literature Cited (1) Am. Sac. Testing Materials, "?Jethods of Chemical Analyses oi Metals," p. 34, 1936. (2) Hoffman, J. I., Bur. Standards J . Research, 8, 659 (1932). (3) Johnson, C. M.,"Chemical Analysis of Special Steels," 4th ed.. pp. 221-33, New Tork, John Wiley &- Sons, 1930. (4) Kolthoff, I. M., and Furman, N. H., "Volumetric Analysis," Val. 11, p. 239, New York, John Wiley & Sons, 1929. ( 5 ) Lundell, G. E. F., Hoffman, J. I., and Bright, H. A., "Chemical Analysis of Iron and Steel," pp. 277-87, S e w York, John Wiley &Sons, 1931. (6) Xoore, T., Chem S e u s , 72, 92 (1895). (7) Partridge, H. hl., ISD.ENG.CHEII.,Anal. Ed., 4, 315 (1932). (8) Peters, F . P., Chemzst-Analyst, 26, 76 (1937). ,RECEIVED January 4 , 1938.
The Symbol Dz to Signify Dithizone P. L. HIBBARD University of California, Division of Plant Nutrition, Berkeley, Calif.
C
OSSIDERABLE literature has accumulated in regard to use of diphenylthiocarbazone (phenylazothionoformic acid phenylhydrazide) as an analytical reagent, Users of this substance soon contracted the name t o dithizone, b u t so far as is known to the writer the only symbol proposed t o represent the name is D. Since this symbol is now commonly used to designate deuterium, the heavy isotope of hydrogen, it should not be uced to represent anything else.
The rvriter propobes the symbol Dz to represent dithizone. This will avoid confusion with anything else and will facilitate writing formulas or equations in which the radical dithizone occurs. TThen the XTord is used as the name of the reagent, diplien~lthiocarhazone. it should be spelled out "dithizone." R T C E I I E DFebruarv 15, 1938.
