Issued February 8, 1911. 



United States Department of Agriculture, 



BUREAU OF CHEMISTRY Circular No. 67. 

 H. W. WILEY, Chief of Bureau. 



A METHOD FOR THE DETERMINATION OF TIN IN CANNED FOODS. 



By HERMAN SCHREIBER and W. C. TABER, 

 Assistant Chemists. 



The determination of tin in canned foods, which has recently become 

 of increased importance, may be made by several methods, each 

 having its advantages and defects. Ashing the material at a very low 

 heat in a muffle will give correct results with some foods under some 

 circumstances, but not always, and when the composition of the mate- 

 rial is not known, it is not safe to apply this method. Moreover, tin 

 and its salts are volatilized by heat in the presence of chlorid of 

 ammonia and probably with other chlorids also, since it is well known 

 that sodium chlorid volatilizes on heating strongly. When small 

 amounts of a metal are to be recovered from a large amount of 

 organic matter, the danger of mechanical loss in the fumes is very 

 great. After ashing, the ash must be fused with caustic alkali if all of 

 the tin is to be recovered, so that this process does not offer any advan- 

 tage over the method herein proposed in regard to the time necessary 

 for making the determination. 



Munson * has proposed carbonizing the organic matter with 

 sulphuric acid and heat, and ashing in a muffle with the aid of nitric 

 acid. Determinations made by this method did not give satisfactory 

 duplicates, and the results represented only about 50 per cent of the 

 tin present, as determined by sulphuric acid digestion (Table 1) in 

 Halenke's wet ashing method, as modified by Schryver. 2 In the 

 latter method the organic matter is destroyed by digestion with large 

 amounts of sulphuric acid with the aid of potassium sulphate. 



1 U. S. Dept. Agr., Bureau of Chemistry Bui. 107, Revised, p. 62. 



2 Report 7 of the Local Government Board (medical department) of Great Britain on the presence of tin 

 in certain canned goods. 



71511-Cir. 6711 



