SULPHATE OF POTASH, POTASSIUM SULPHATE 235 



It is very generally stated that potassium chloride affects 

 the burning quality of tobacco and makes potatoes watery. 

 The former is probably true, but the latter is not always the 

 case, for excellent potatoes can be grown with the chloride, 

 provided, however, that lime has been applied to the soil. 

 The bad effects of the chlorine are apparently most pro- 

 nounced on acid soils. 



The tendency of potassium chloride is to make a soil 

 acid (Section 186). Plants exercising their selective action 

 remove the base, potassium, from the soil and leave the 

 chlorine which is assimilated but little. This results in the 

 production of hydrochloric acid which neutralizes any basic 

 compound present in the soil, and this means usually calcium 

 carbonate. When the reserves of base are used up the soil 

 becomes acid. The calcium chloride thus formed is easily 

 leached from the soil. Potassium chloride removes calcium 

 from the soil in another way by reacting with calcium 

 silicates to form potassium silicates and calcium chloride 

 which is, of course, leached out. 



179. Sulphate of Potash, Potassium Sulphate, K 2 S0 4 . — This 

 fertilizer, although not used to so great an extent as the 

 muriate, is in many respects the best one to employ. It is 

 made by dissolving and concentrating a mixture of potassium 

 chloride and kieserite (magnesium sulphate). There is 

 precipitated the double sulphate of potassium and magnesium 

 (K 2 S0 4 .MgS04), which is also sold under the name of Double 

 Potash Manure Salt, containing about 27 per cent, potash. 

 This double salt is further dissolved with a certain amount 

 of potassium chloride and boiled. Potassium sulphate is 

 precipitated. Two grades are sold, 90 and 96 per cent, pure, 

 containing, respectively, 47 per cent., and 52.7 per cent, 

 potash. 



Potassium sulphate has no bad effects on tobacco and 

 potatoes, and, furthermore, is not so apt to make a soil acid, 

 since plants assimilate sulphur to a considerable extent. 

 The whole salt is thus absorbed and no residue left. This 

 fertilizer has an action on calcium silicates similar to that 

 of the chloride, but the resulting calcium sulphate is not so 

 soluble as calcium chloride, nor is it leached to so great an 



