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owing to the somewhat complicated and tedious nature of 
the operations required. The modifications described in the 
following communication considerably simplify the process, 
and may possibly lead to its more general adoption. 
Reissig’s method depends upon the fact that, when 
metallic tin is added in excess to a solution of the phos- 
phate of the alkaline earths in nitric acid, the stannic acid 
formed by the oxidation of the metal combines with the 
phosphoric acid and completely removes it from solution. 
On filtering, therefore, we at once separate the alkaline 
earths which remain in solution from the insoluble combi- 
nation of stannic and phosphoric acids. In order to deter- 
mine the amount of phosphoric acid contained in the tin 
oxide, the compound is dissolved in a small quantity of 
concentrated potash solution, when the two acids dissolve 
as meta-stannate and phosphate of potassium : the fluid is 
now saturated with hydrogen sulphide, a small quantity of 
ammonium pentasulphide added, and, lastly, a slight excess 
of acetic acid. The tin sulphide is then separated by fil- 
tration : all the phosphoric acid is contained in the filtrate, 
and its amount may be determined by the ordinary method 
as magnesium ammonium phosphate. 
The chief disadvantage of this method arises from the 
necessity of employing a large excess of metallic tin, in 
order to completely remove the phosphoric acid from solution. 
The bulk of tin sulphide obtained is therefore very large, and 
its filtration and washing is an exceedingly long and tedious 
operation. In order to shorten the process, Reissig recom- 
mends that the alkaline solution of the phosphate and 
stannate be transferred to a weighed flask of 1000 cubic 
capacity, and then diluted with water until the fluid 
measures about 900 cubic; the solution is next saturated 
with hydrogen sulphide, then ammonium sulphide and 
acetic acid in slight excess added, and the tincture diluted 
until the whole weighs 1000 grams. After standing for a 
