262 AGRICULTURAL ANALYSIS 



point of view, except in the decomposition of phosphates with 

 sulfuric acid, where the evolution of hydrofluoric acid or hydro- 

 fluosilicic acid may cause grave inconvenience to the workman 

 and damage to the apparatus. It is important to know the exact 

 content of a phosphate in fluorin before submitting it to the pro- 

 cess of manufacture, by means of which phosphoric acid is ren- 

 dered soluble in water and ammonium citrate. The principles 

 upon which the estimation of the fluorin depend, comprise both 

 the decomposition of the substance by fusion with the carbonate 

 of soda and silica, and the estimation of the fluorin in the 

 hydrofluosilicic acid evolved by the simultaneous action of con- 

 centrated sulfuric acid and silica upon the fluorin compound. The 

 last method theoretically leads to the realization of the conditions 

 necessary for an exact determination, but in practice it has been 

 found to be attended with very great difficulties. The assump- 

 tion that the hydrofluosilicic acid is evolved in the pure state is 

 wot always correct, since phosphates contain quite commonly 

 some carbonates and organic matters, and even chlorids. When 

 these compounds are treated with concentrated sulfuric acid, there 

 is set free some sulfurous, carbonic, and hydrochloric acids, and 

 these escaping in a gaseous form, are likely to carry with them 

 also some water vapor. In the application of this method it has 

 therefore been found necessary to previously ignite the phosphate, 

 and this operation is also open to objections. In case calcination 

 is practiced, it is necessary to carry it so far that there remains 

 no trace of carbonic acid, or of carbon, for the presence of these 

 bodies would interfere seriously with the subsequent determina- 

 tion of the fluorin. Even when this method can be successfully 

 practiced with natural phosphates, it will be found extremely diffi- 

 cult of application in the estimation of any residual fluorin in 

 superphosphates. 



226. Estimation of Fluorin by the Method of Berzelius as 

 Modified by Chatard. The method of estimating fluorin as pro- 

 posed by Berzelius has been found quite satisfactory in the labo- 

 ratory of the Geological Survey, with the modifications given be- 

 low. 28 



M Transactions of the American Institute of Mining Engineers, 1892-93, 

 21 : 170. 



