192 The Philippine Journal of Science isie 



them the mechanical removal ^^ of the tin after heating over 

 a Bunsen flame ; the digestion at boiling temperature with sodium 

 peroxide/^ the difference in weight before and after treatment 

 serving as an indication of the amount of coating; the solution 

 of the tin coating in 12.5 per cent hydrochloric acid ^^ and sub- 

 sequent precipitation of the tin as sulphide, heating, and final 

 weighing as oxide; the solution in 10 per cent hydrochloric 

 acid," precipitation with ammonium sulphide, and heating, after 

 certain precautions, with ammonium carbonate ; and the heating 

 of tin plate with dry sodium peroxide,^^ solution of the melt 

 in water, acidifying with sulphuric acid, washing, heating, and 

 weighing the precipitated oxide. I. H. Aupperle " suggests (1) 

 the solution of the tin in hydrochloric acid, with certain pre- 

 cautions, and the final determination of tin by titration with 

 iodine solution, or (2) the removal of tin with concentrated 

 sulphuric acid and the determination of the iron in the solution, 

 the tin being obtained either by difference or by direct analysis 

 as above. 



The above methods either give merely the amount of tin 

 present or else the total amount of plate (tin, lead, and iron alloy 

 in the coating). If the amounts of tin and lead are desired, 

 additional processes are required. 



Directions for a simple method for the determination of lead, 

 as given by Serger," are as follows: 



Take 0.1 gram iron-free tin, carefully scraped from heated 

 tin plate, decompose with 3 cubic centimeters of concentrated 

 nitric acid on a steam bath, and evaporate to dryness three 

 times. Add 10 cubic centimeters of water, allow to stand on 

 a water bath for ten minutes, filter into a 100 cubic centimeter 

 flask, and dilute to the mark with distilled water. Shake well, 

 use 10 cubic centimeters in a large test tube, and add 10 cubic 

 centimeters of fresh hydrogen sulphide water. Compare the 

 color obtained with a standard made by adding 2, 5, 10, and 

 20 drops of a water solution, containing 0.16 gram of lead 

 nitrate per 100 cubic centimeters (1 cubic centimeter=0.001 

 gram metallic lead) to 10 cubic centimeters of water and 10 

 cubic centimeters hydrogen sulphide water. 



" Serger, loc. cit. 



"Meyer, K., Zeitschr. f. angew. Chem. (1909), 22, 68. 



" Serger, loc. cit. 



"Mastbaum, H., Zeitschr. f. angew. Chem. (1897), 10, 329. 



"Angenot, H., ibid. (1904), 17, 521. 



''Metal. Ind. (1914), 12, 327-328. 



" Loc. cit. 



