SULPHURIC ACID. 41 



Being soluble in 400 times its bulk of water, gypsum 

 supplies to plants both sulphuric acid and lime, 

 perhaps directly. Its great value lies in its action 

 upon ammonia, which in its usual form of carbonate 

 of ammonia is exceedingly volatile. For this it 

 proves a most excellent and effective trap — a trap 

 which a good farmer should not fail to keep well set 

 in his stables and on manure heaps. The sulphuric 

 acid exerts its superior power by tearing the ammo- 

 nia from its combination with carbonic acid and 

 taking it to its own heart, forming the compound 

 ^'sulphate of ammonia," (which is held in the soil or 

 manure until taken up by the plants, or converted 

 into nitrates), and leaving the carbonic acid and 

 lime to get along as best they may in 



^^^i?^" the new union of carbonate of lime. 

 Here again we have sulphuric acid m 

 the role of caterer or provider of plant food to needy 

 crops. 



In a practical treatise we have little occasion to 

 speak of the compounds of sulphuric acid with soda 

 and magnesia, sulphate of soda and sulphate of 

 magnesia, as we do not need to apply them as plant 

 foods. Sulphate of potash, the combination of sul- 

 phuric acid and potash, will be spoken of later on. 



The compound sulphate of iron (green copperas, 

 iron vitriol) is reported to have been applied to the 

 soil with apparently beneficial effect, adding luxuri- 

 ance to the foliage, and darkening the green color. 

 But this cannot possibly be due to its character as 

 a plant food, and may find its explanation in the 

 action of the acid, either upon plant foods already 

 in the soil, making them available when locked up, 

 or upon the spores of fungous diseases of plants, 

 depriving them of their power of germination. 



