106 COMPOSITION AND PROPERTIES OF THE 



4. On different crops, either as a watering after the seed is 

 sown, when it has come up and is especially liable to injury 

 from insects, or when, in April or May, the young plants have 

 already attained a considerable size. 



Though, as I have already said, the beneficial action of 

 sulphuric acid may be ascribed to its 'forming gypsum in the 

 soil, yet the reader will understand that the peculiar action of 

 this acid upon organic matter may also be a cause of the sen- 

 sible effects which follow its application. It may also be 

 because its action is really of this kind, that, when applied 

 in the least diluted state, its effects were the most striking 

 in some of the experiments of Tinzmann. At all events, the 

 possibility of so explaining its action adds to the interest of 

 experiments made with it, and more strongly recommends the 

 prosecution of them. 



3. Composition and general properties of the sulphates of 

 potash, soda, lime, magnesia, and iron. 



1. Sulphate of potash is colourless ; crystallises in double six- 

 sided pyramids ; undergoes no change by exposure to the air ; 

 dissolves in 9 parts of water at 60 F. ; has a slight saline, bitter 

 taste; decrepitates in the fire; is without smell; and produces no 

 sensible action upon animal or vegetable substances. When 

 pure, it consists, in 100 parts, of 



Sulphuric acid, . . . . . 45' 93 

 Potash, 54-07 



100 



2. Sulphate of soda, (Glauber's salt,) is also colourless, and 

 without smell. It crystallises in long striated four-sided prisms, 

 and these crystals effloresce, or fall to a white powder, in a dry, 

 warm atmosphere. When dry and uncrystallised, however, it 

 undergoes no change by exposure to the air. The crystals dis- 

 solve in 14 parts of water at 32 F., but in less than 5 parts at 

 60 F. When heated, the crystals melt or dissolve in then 1 own 

 water of crystallisation. When free from water, or dry, sul- 

 phate of soda dissolves in 20 parts of water at 32 F., and in 7 

 parts at 60 F. It has a peculiar cooling, bitter taste, and is 



