If tin is to be estimated in foods, such as fish, which contain so 

 great an amount of salt as not to be edible before soaking, it is better 

 to determine the tin by the sulphuric-acid method, as large amounts 

 of salt would interfere with the burning off of the carbon by the 

 proposed method. However, such cases wculd be very rare, as salt 

 fish are commonly packed in wood and not in tin. 



The method proposed on page 6 requires practically no experience 

 in its manipulation, and a large amount of the sample is used, in 

 both of which points it is superior to the wet combustion method. 

 It was at first thought that the destruction of the organic matter 

 could be effected by an alkaline fusion, using alkaline hydrate and 

 nitrates. However, when material, such as fish, which contains fat, 

 is to be analyzed, it is impossible to make such a fusion, as it will 

 burn and blow out of the crucible. When alkaline hydrates are 

 used alone, a solid cake results which retards the complete destruc- 

 tion of carbon by coating the small particles. A mixture of hydrate, 

 carbonate, and magnesium oxid was found to give a very porous 

 fusion, in which the carbon was easily oxidized in the muffle. The 

 fusion was at first attempted in large nickel crucibles with very 

 good results as shown by Table 5. 



TABLE 5. Comparison of the sulphuric-acid or wet combustion method with alkali fusion 

 in a nickel crucible by the proposed method. 



[Grams of tin per 50 grams of sample.] 



The nickel crucibles, however, were very seriously attacked, and 

 since they are expensive, it was thought that fusion in an iron crucible 

 would be a great advantage on account of the lower cost and the 

 higher melting point of iron. When iron crucibles were first sub- 

 stituted, the results obtained were lower than by the wet combustion 

 method, and a repetition of the determination gave no solution of the 

 difficulty. At this time hydrochloric acid was used for dissolving 

 the fusions and finally, on the theory that the trouble was due 

 to the solvent action of the iron chlorid on the tin, sulphuric acid was 

 substituted for hydrochloric acid and correct results were obtained, 

 as shown in Table 6. 



[Cir. 67] 



