268 



AGRICULTURAL ANALYSIS 



into a solution of caustic soda, where the fluorin is retained and 

 ultimately estimated. It does not matter that the fluorin in this 

 case is accompanied with other gases, and with vapor of water, 

 since these impurities are absolutely without inconvenience in 

 the subsequent proceedings. The phosphates can be treated with- 

 out previous calcination or preparation in any form, and after 

 mixing with sulfuric acid the temperature can be raised just to 



Dry a i 



Aapircctor 



Fig. 12. l.asnc's Apparatus. 



the point of ebullition, which promotes very greatly the speed 

 of the reaction and the perfect separation of the fluorin. The 

 operation is conducted as follows: 



A definite quantity of the phosphate or any other body what- 

 ever containing fluorin, provided it be decomposable by sulfuric 

 acid, is introduced into a dry flask in which have been previously 

 placed about 50 cubic centimeters of strong sulfuric acid and 10 

 grams of finely ground sand. The quantity of the phosphate em- 

 ployed should be such as to secure, if possible, an amount con- 

 taining o.i gram of calcium fluorid. In phosphates which are 

 very poor in fluorin it will be necessary to use from 10 to 20 

 grams. One of the great advantages of this process lies in the fact 

 that it permits the employment of these great quantities of 

 materials without in any way interfering with the accuracy of 

 the analysis. The flask and receiving bottles employed in the 



