392 



AGRICULTURAL ANALYSIS 



The typical reactions which take place are represented in the 

 following equation : 



6FeCl 2 +2KNO 3 +8HCl=3Fe 2 Cl 6 +2KCl+4H 2 O+2NO. 

 346. Schloesing's Modified Method. The schloesing method 

 as now practiced by the French chemists is conducted in the ap- 

 paratus shown in Fig. 20. 39 The carbon dioxid is generated by 

 the action of the hydrochloric acid in F on the fragments of 

 marble in A. After passing the wash-bottle, the gas enters the 

 small tubulated retort, C, which contains the nitrate in solution. 

 When the quantity of nitrate is small, as in ordinary soils, 100 

 grams are placed in an extraction flask, plugged with cotton, and 



Fig. 20. Schloesing's Apparatus for Nitric Acid. 



a layer of the same material is placed over the soil for the pur- 

 pose of securing an even distribution of the extracting liquid. 

 This liquid is distilled water containing in each liter one gram 

 of calcium chlorid. The purpose of using the calcium chlorid is 

 tc prevent the soil from becoming compacted, which would ren- 

 der the extraction of the nitrate difficult. The extracting liquid 

 is allowed to fall, drop by drop, from a mariotte bottle until the 

 filtrate amounts to 500 cubic centimeters. This volume* is con- 

 centrated on a sand-bath until it is reduced to 10 or 15 cubic cen- 

 timeters, when it is transferred to a flat-bottomed dish and the 

 evaporation finished over steam, care being taken not to allow 

 the temperature to exceed 100. 



39 Encyclopedic chimique, 1888, 4 : 151. 



