AGRICULTURAL ANALYSIS 



a mixture of chlorids or nitrates of potash and soda in solution, 

 perchloric acid is added and the mixture evaporated on a sand 

 bath until it is almost dry. The degagement of white fumes is a 

 sign that perchloric acid is in excess and that the formation of 

 the salt is complete. When the white fumes have ceased to come 

 over, the mass is cooled and the perchlorate of potash is washed 

 several times with small quantities of alcohol of 36. The more 

 abundant the soda, the more perchlorate of potash is retained in 

 its crystals. For this reason it is advisable to dissolve with heat 

 in the least quantity of water possible the perchlorates when 

 they are almost washed, and to evaporate to dryness. Two wash- 

 ings with alcohol will then finish the purification of the salt. 

 With a few drops of water the perchlorate which is retained 

 upon the filter is dissolved and received into a capsule, evap- 

 orated again to dryness and heated to 250. The salt is then 

 absolutely dry and fit to weigh. The alcoholic solution of per- 

 chlorate of soda is evaporated, the salt is afterwards decomposed 

 by heat, taken up by water and evaporated in a platinum capsule. 

 The chlorid of soda thus obtained very often contains some trace 

 of perchlorate. In order to have an exact estimate it is neces- 

 sary to transform it into sulfate. In place of decomposing the 

 perchlorate of soda by heat, it may be treated directly by sul- 

 furic acid. 



The paper gives data showing the exactitude of the reaction 

 and describes the preparation of perchlorate of ammonia, which is 

 the reagent employed to furnish the perchloric acid. 



489. Caspari's Method for Preparing Perchloric Acid. A 

 hessian crucible about 15 centimeters high is filled with moder- 

 ately well compressed pure potassium chlorate and gradually 

 Tieated in a suitable furnace until the contents become fluid. 64 

 The heat must then be carefully regulated to avoid loss by foam- 

 ing due to the evolution of oxygen. The heat is continued until 

 oxygen is no longer given off and the surface of the liquid be- 

 comes encrusted, which will take place in from one and a half 

 to two hours. 



After cooling, the contents of the crucible are pulverized and 

 ** Zeiischrift fur angewandte Chemie, 1893, 6 : 68. 



