TABLE 7. Comparison of results by the wet combustion method and proposed method 

 using blue ribbon filter papers and sulphuric acid. 



[Grams of tin in 50 grams of sample.] 



1 These tin oxids were only very slightly discolored, being very nearly the same shade as those from 

 the wet combustion. 



The proposed method has several advantages over the wet combus- 

 tion method: (1) It decreases the errors of sampling; '(2) it decreases 

 the errors due to multiplication when calculating to milligrams per 

 kilogram; (3) there need be no loss of samples if the material is 

 properly ground and not heated too rapidly on the hot plate ; (4) in 

 the wet ashing methods it is necessary to neutralize a large amount 

 of acid before precipitating with hydrogen sulphid. 



Molasses and heavy sirups must be dried longer on the hot plate 

 than any other material analyzed, over three hours being necessary 

 to dry these properly. However, as it requires no attention at this 

 stage, this is not a serious defect as compared with the difficulties of 

 determining tin by the wet ashing method. In drying any material 

 on the hot plate it is not necessary to dry it down to a hard crust if 

 it is put in a cold muffle and heat applied gradually. If tin is to be 

 determined in oils, less of the sample should be used, so that there 

 will be an excess of free sodium hydrate. The sulphuric acid method 

 for the determination of tin can not be applied to oils, and therefore 

 no comparison of the two methods can be made. 



THE PROPOSED ALKALI FUSION METHOD. 



Pass the sample through a meat- grinding machine and mix the resulting mass well 

 BO as to get as homogeneous a sample as possible. Weigh 100 grams of the sample and 

 10 grams of magnesium oxid into an 8-ounce wrought-iron crucible on a rough balance. 

 Add 50 c. c. of an aqueous solution containing 150 grams of sodium hydrate and 100 

 grams of sodium carbonate per liter, stir well with a short piece of stout glass rod, add 

 75 c. c. of 95 per cent alcohol and stir again. Place on the steam bath and evaporate 

 the alcohol. This must be done with care, stirring frequently at the beginning, else 

 it may bump or foam over, but if the material is gradually heated there is no danger 

 of loss. If the material foams, remove from the steam bath or hot plate for a moment, 

 [Cir. 67] 



