308 CHEMICAL MANUEES. 



2 to 3 per cent of impurities, potassium chloride and potassium 

 sulphate. This salt, therefore, contains very little chlorine and 

 might perhaps he used as a fertilizer for tohacco. But the price of 

 potassium is about double in it to what it is in potassium sulphate. 



Potash not only acts as a manure but it retains the moisture in 

 the soil. Certain potash salts absorb moisture and cake ; kainit 

 especially forms very hard blocks like stone. Spread in a thin layer 

 it absorbs 2 per cent of moisture in twenty-four hours. 



Calcined potash salts absorb from dry air up to 6 per cent of 

 water, in five days 14 per cent, and up to 24 per cent in six days. 

 To prevent them caking into a solid mass it suffices to add 2-5 per 

 cent of peat powder ; the mixture so prepared keeps for two months 

 without drawback. 



Other Fertilizing Salts. — The Stassfurt factories sometimes 

 make a fertilizer from other waste not hitherto utilized. For this 

 purpose the sludge deposited at the bottom of the clarification pans, 

 which always contain a little potash, is used. 100 parts of calcined 

 ground shidge contain : — 



TABLE C v.— ANALYSIS OF SLUDGE FROM CLAPJFICATION OE 



POTASH SALTS. 



Insoluble (oxide of iron, sand, gypsum) . 6*34 

 Calcium sulphate .... 8'67 



Double sulphate of potassium and 



magnesium (MgSOj -h KiSO^l 

 Potassium chloride 

 Magnesium ,, ... 



Common salt .... 

 Water and loss .... 

 Say 19-35 KCl or 22-o4 sulphate of 



potash 



100-00 12-22 



Another product of this kind is furnished by the residual salt which 

 contains about 12 per cent of potassium sulphate ; as we have seen, 

 this consists of sludge and especially of common salt. 



A third salt likewise used as a fertilizer is that extracted from 

 the gutters, which when diy contains about 50 per cent of potassium 

 chloride, and 45 to 50 per cent of common salt. 



All these salts are treated in the same wav. Thev are dried 

 in a reverberatory furnace by heating them to nearly the point 

 of fusion, then they are crushed. Brown fertilizing salts with low 

 potassium content are hardly met with now on the market. The 

 salt from the gutters dried and ground is sold under the name of 

 " manure salt, calcined and ground," with a minimum guarantee of 

 27 per cent of potassium. Lately a whole series of other potassic 

 manures has been manufactured, but their high price is an obstacle 

 to their sale. The composition of the different Stassfurt salts are 

 summarized in the following table : — 



