5 



TABLE 6. Comparison of results by the wet combustion method and the proposed method, 

 using different solvents and an iron crucible. 



[Grams of tin in 50 grams of sample.] 



The results reported in Tables 4 to 7 were obtained in the prelimi- 

 nary work done in developing the proposed method. In the method, 

 as then used, 5 grams of magnesium oxid were employed, and the 

 solution of the fusion was not concentrated until it fumed with 

 sulphuric acid, but was simply boiled down, and blue ribbon paper 

 was used for the first filtration. It was found that the fusions could 

 be burned at a lower temperature if 10 grams of magnesium oxid were 

 used, which makes the burning much easier and materially lengthens 

 the life of the crucible. It was also found best to use a larger amount 

 of acid, as specified in the method, since under certain circumstances 

 all of the tin was not dissolved when only 50 c. c. of 1 :1 sulphuric acid 

 and 5 c. c. of nitric acid were used. The use of blue ribbon paper was 

 also abandoned, since it decreased the speed of filtration, and, further- 

 more, it has no apparent advantage (Table 7) when the precipitation 

 is made as specified in the proposed method. The experimental data 

 indicate that sulphuric acid alone will not take all of the tin into 

 solution, although no explanation of this can be offered. 



[Cir. 67] 



