114 NOTES [Vol. 76 THE DETERMINATION OF ZINC. OXIDE IN ZINC POWDER ZINC powder always contains a small proportion of zinc oxide; several methods for the determina- tion of the amount of this impurity are mentioned in the literature, but these are mostly based on the reducing power of the zinc. This may be measured by several reactions, e.g., potassium bichromate, iodate, ferric sulphate and iodine. Fresenius proposed dissolving the zinc dust in dilute sulphuric acid and, after drying the gas, passing the resultant dry hydrogen over heated copper oxide in a combustion tube, absorbing the water formed in a calcium chloride tube. None of these methods is really satisfactory in that the results obtained by these different methods are not concordant and are not reproducible by the same method.The method most widely used in specialised laboratories is that based on the volurne of hydrogen evolved when a sample of zinc dust is dissolved in dilute sulphuric acid; here again the zinc is measured, but the apparatus and technique is very complicatedl and not suitable for the chemist who has only an occasional sample to examine. Another method has recently been described in America,2 but again the apparatus and technique required are beyond the reach of any but the specialist. Confronted by this problem, we have devised a simple but accurate method based on experi- mental evidence that showed that zinc oxide is soluble in ammonium acetate solution whilst zinc metal is not, and it may well prove of use to the chemist who has only an occasional determination to make.Procedure-Take 2 g of the powder in a 250-ml beaker and add 100 ml of water containing 30 g of ammonium acetate. Filter on a sintered glass of No. 4 porosity with suction, and wash with cold water. If washed with absolute alcohol or sodium-dried ether, the zinc can be weighed after drying by suction and placing in a vacuum desiccator for 15 minutes. If a chemical finish is desired, dissolve the residue in hot dilute sulphuric acid, cool, add an excess of caustic soda and electrolyse the zinc, a copper-coated cathode being used. Alternatively, the zinc may be precipitated as the sulphide, and converted to the oxide in the well-known manner. This result gives the amount of zinc metal present. Stir well for 10 minutes, and then allow to stand for 2 hours.Feb., 19511 NOTES 115 The zinc oxide that has been dissolved out by the ammonium acetate can be determined by precipitation with hydrogen sulphide after addition of 10 ml of ammonia.When all the sulphide has precipitated, boil with a little paper pulp to help coagulation. Filter on sintered glass of No. 2 porosity with a paper-pulp pad and suction. Dissolve the residue in 6 N sulphuric acid and boil. Filter on sintered glass and wash well with hot water. Add an excess of caustic soda and, after cooling, electrolyse the solution on a copper-coated cathode in the usual manner. Calculate to ZnO. The author thanks the Directors of the British Drug Houses Limited for permission to publish this note. REFERENCES 1. 2. Furman, N. H., “Scott’s Standard Methods of Chemical Analysis,” Fifth Edition, Volume I, Balis, E.W., Bronk, L. B., and Liebhafsky, H. A., Anal. Chein., 1949, 21, 1373. D. Van Nostrand Co., New York, 1939, p. 1069. ANALYTICAL DEPARTMENT THE BRITISH DRUG HOUSES LIMITED POOLE, DORSET LABORATORY CHEMICALS GROUP G. H. OSBORN July, 1950 1-NITRO-2-NAPHTHOL AS A REAGENT FOR ESTIMATING COBALT ~-NITRO-~-NAPHTHOL is described in some modern textbooks1-2 as a precipitant for cobalt that is superior to the more usual l-nitroso-2-naphthol. We find that pure 1-nitro-2-naphthol does not give a precipitate with cobalt. This is in agreement with Mayr and Prodinge? who reported that the reagent used previously by Herfeld and Gerngross,4 and by Mayr,s which actually pre- cipitated cobalt, must have contained l-nitroso-2-naphthol.l-Nitro-2-naphthol is prepared by oxidising 1-nitroso-%naphthol with nitric acid,1 and the above-mentioned erroneous observations appear to be due to a difficulty in separating the nitro- compound from the nitroso-compound. We have found that l-nitro-2-naphthol can be separated from the crude oxidation product by steam distillation and finally purified by crystallisation from alcohol. The steam distilled l-nitro-2-naphthol melted at 101’ to 103” C; after one crystallisation from alcohol the melting-point was 103” C, in agreement with the figure recorded in the literature.6 Acknowledginent is made to the Chief Scientist, Ministry of Supply, foi- permission to publish this note. 1. 2. 3. 4. 5. 6. REFERENCES Vogel, A. I., “Textbook of Quantitative Inorganic Analysis,” Longmans, Green and Co., London, 1948, pp. 164, 548. Yoe, J. H., and Sarver, L. A., “Organic Analytical Reagents,” John Wiley and Sons Inc., New York, 1941, pp. 129, 245. Mayr, C., and Prodinger, W., 2. anal. Chew., 1939, 117, 334. Herfeld, H., and Gerngross, O., Ibid., 1933, 94, 7. Mahr, C., Ibid., 1934, 98, 402. Heilbron, I., and Bunbury, H. M., “Dictionary of Organic Compounds,’’ Eyre and Spottiswoode, Londm, 1946. MINISTRY OF SUPPLY, EXPLOSIVES RESEARCH AND DEVELOPMENT ESTABLISHMENT WALTHAM ABBEY ESSEX N. J. BLAY L. A. WARREN -July, 1950 A COLOUR TEST FOR AMPHETAMINE IN the test for cocaine previously described by the author,l amphetamine gives a purple colour similar to that of cocaine; the colour, however, changes in about 7 minutes to a beautiful violet colour. The test will detect 0.025 mg of amphetamine. A strong reaction is given by 0.1 mg of amphetamine. REFERENCE 1. Rathenasinkam, E., Analyst, 1950, 75, 169. GOVERNMENT ANALYST’S LABORATORY COLOMBO E. RATHENASINKAM CEYLON July, 1950