M. Chancel on the determination of Phosphoric Acid. 381 
uranium, yields chalcolite, PO°®, 2CuO + PO® (Ur? 08)4+16HO, 
or double phosphate of copper and uranium. 
Chancel proposes * the following method of separating and 
estimating phosphoric acid in the presence of bases: it depends 
on the insolubility of phosphate of silver, 3AgO, PO®, ina neutral 
liquid. 
The substance taken is dissolved in the least quantity of dilute. 
nitric acid, and the solution diluted with water. The clear 
liquid is mixed with a sufficient quantity of nitrate of silver, 
and then with a slight excess of carbonate of silver. This opera- 
tion must be performed in the cold when the liquid contains 
any substance, such as manganese, which is precipitated by the 
application of heat. 
The phosphoric acid soon separates as yellow phosphate of 
silver ; the precipitation is complete when the liquid no longer 
reddens blue litmus paper ; the precipitate is then filtered, care- 
fully washed, introduced into a flask, and dissolved in nitric 
acid. ‘The silver is now precipitated by means of hydrochloric 
acid and the filtered liquid supersaturated with ammonia, and 
the ammoniacal phosphate precipitated with sulphate of mag- 
nesia in the ordinary manner. 
The advantages which silver salts have in this separation of 
phosphoric acid, consist greatly in the readiness with which the 
silyer is removed from the solution; but they have the great 
disadvantage that, when the phosphoric acid is in combination 
with alumina, oxide of iron or chrome, it is not separated from 
these bodies, but merely precipitated with them. The use of 
bismuth compounds which Chancel proposes} is not amenable to 
these objections; it furnishes an exact and easy method, one 
susceptible of the widest application. 
The method depends on the insolubility of phosphate of 
bismuth in liquids which contain even a considerable propor- 
tion of free nitric acid. The acid nitrate of bismuth is pre- 
pared by dissolving one part of pure subnitrate of bismuth 
(BiO?, NO®+ Aq) in four parts of nitric acid of sp. gr. 1:36., 
and adding to the solution thirty parts of water. Thus prepared, 
the solution is not made turbid either by boiling or by the 
addition of any quantity of water. The substance to be de- 
termined is dissolyed in distilled water; if necessary a small 
quantity of nitric acid is added, care being taken to avoid excess, 
and the solution diluted with water. If the solution contains 
sulphates or chlorides they must be removed, the former by 
adding nitrate of baryta, and the latter by nitrate of silver. The 
solution of acid nitrate of bismuth is then added, as long as a 
* Comptes Rendus, December 1859. + Ibid. February 27, 1860. 
