302 CHEMICAL MANURES. 



but now all the fac Lories have laid down mechanical crushers for 

 the purpose ; the machine most used is the jaw-breaker crusher 

 already described. ^ 



Dissolving the Crude Salts. — The salt is then fed into a pan, 

 in which it is dissolved. The crushed salt falls from the mill into 

 the receiver of a cup-elevator, which delivers it directly into the 

 dissolving pans or into a wrought-iron shoot. The elevator is 

 driven by a shaft on which is mounted the belt pulley. The dis- 

 solving pan is of riveted wrought-iron of a cylindrical form ending 

 in a conical bottom. At the beginning of the cone is a perforated 

 short bottom intended to retain the residues from the salt. These 

 residues are run out through a manhole. The solution is drawn 

 off by a tap, the pan is steam heated. In the early days the 

 Stassfurt and Leopoldshall factories wrought in an appreciably uni- 

 form style, but lately thej^ have adopted ditierent methods more con- 

 formable to the interests of each factory. The oldest method, still 

 much employed, is the following : The dissolving pan is first partly 

 charged with water, mother liquor, which is termed II, with residual 

 solution I (see further on) and with clarified solution III (see further 

 on). After having brought this mixture to the boil, by direct injection 

 of steam, the crude salt is fed into the elevator, whilst continuing to 

 boil without interruption ; the carnallite soon dissolves and therefore 

 ±he density of the solution increases gradually ; the escaping steam 

 by a suitable arrangement sets the liquid in motion and mixes its 

 different components. When the density of the liquid, taken on a 

 boiling sample, reaches S2^ to 33" B., the elevator is stopped, the 

 steam turned off and the solution run out ; the residue remaining in 

 the pan contains a large proportion of kieserite, common salt, and 

 about 2 to J: per cent of potash salts. In a great number of 

 factories this residue is again taken up and boiled with a little 

 water ; the solution thus obtained (I) consists therefore chiefly of 

 common salt, a little magnesium chloride and magnesium sulphate. 

 Its potassium content varies from 3 to 7 calculated' as potassium 

 chloride ; it is used solely to dissolve fresh quantities of crude salt. 

 The proportions of the different solutions as well as the densities 

 varv with the factorv. The residues are thus more or less abund- 

 ant and retain more or less salts. The best results are obtained by 

 preparing solutions of 32° B. with lower densities ; they retain a large 

 amount of common salt ; when on the contrary their density is 

 higher, they retain less common salt and more potassium chloride. 



Clarification. — Crude solution as it comes from the pan is 

 soiled with impurities ; it is therefore run into clarification basins, 

 where it remains for about fortv-five minutes. These basins are 

 rectangular, of riveted wrought-iron, fitted with two apertures, 

 from one of which the clarified solution is run off, and from the 

 other the sludge. To prevent the clarified solution carrying the 



