280 Dr Colquhoun on the Assay 



acid in union with barytes. This precipitate is to be washed, 

 dried, and ignited. 100 parts of it will prove equivalent to 

 13.56 parts of sulphur. 



Phosphorus, on those rare occasions in which it exists in the 

 ore, appears to be in the state of phosphoric acid, combined, 

 probably, either with lime or with oxide of iron. In order to 

 ascertain its amount, dissolve from 50 to TOO grains of the ore 

 in nitric or muriatic acid, taking the necessary precautions to 

 peroxidize the whole of the iron. Filter the clear liquid from 

 the insoluble matter, and add a slight excess of ammonia to it. 

 The oxide of iron which will, by this means, be precipitated, 

 will carry down in combination with it the whole of the phos- 

 phoric acid. After this precipitate has been washed, mix it 

 in a silver crucible, with a concentrated aqueous solution of 

 twice or thrice its weight of caustic potash or soda, evaporate 

 the mixture rapidly to dryness, and stir it constantly during 

 the whole process to prevent any portion of it from being 

 thrown out, after which, let the dry residue be ignited in a 

 pretty strong red heat for half an hour. Digest the fused 

 mass in water : the oxide of iron will remain untouched, but 

 the phosphoric acid, now in combination with the alkali, will 

 pass into solution. Neutralize the liquid with nitric acid, heat 

 it, in order to expel all traces of carbonic acid, then render it 

 alkaline by the addition of an excess of caustic ammonia, and 

 lastly, pour in a solution of muriate or nitrate of lime. Phos- 

 phate of lime will fall down, in the form of a gelatinous pre- 

 cipitate : it may be collected upon a filter, washed, dried, and 

 ignited. 1 00 parts of the phosphate, obtained in this manner, 

 contain, according to Berzelius's analysis, about 48.4 parts of 

 phosphoric acid. 



The proportion of carbonic acid contained by any ore may 

 be ascertained in an approximative manner by putting a deter- 

 minate weight of it, (as, for example, 50 or 100 grains) pre- 

 viously broken down into fragments into a platinum crucible, 

 and exposing it to a brisk red heat for fifteen minutes. The 

 whole of the carbonic acid will be expelled by this treatment, 

 and its amount will be represented by the loss of weight which 

 the mineral sustains. When an ironstone is subjected to ig- 

 nition, however, it is liable to undergo several other alterations 



