378 MISCELLANEOUS PRODUCTS USED IN AGRICULTURE. XVI. 



surrounded by boxes to enclose the heavy vapour given off 

 from a small quantity (5 or 10 c.c.) of the liquid placed in a 

 saucer. It is, however, particularly well adapted for the 

 destruction of subterranean insects or their larvae. For this 

 purpose a hole from 6 to 12 inches deep is made, not too near 

 the tree whose root is affected by the insects, and from 15 to 

 30 c.c. of carbon disulphide poured in. The hole is then 

 quickly closed, when the vapour diffuses into the soil and 

 destroys the insects. Carbon disulphide is also employed to 

 rid grain of insects. 



The extreme inflammability of its vapour renders carbon 

 disulphide dangerous to use in the neighbourhood of flames. 



Iron Sulphate, FeSO 4 .7H. 2 O, cop2)cras, green vitriol. This 

 substance is prepared by the action of dilute sulphuric acid 

 upon scrap iron; sometimes by the oxidation, by means of 

 damp air, of marcasite or white pyrites, FeS 2 ; or as a bye- 

 product in the manufacture of alum from "alum schists," 

 i.e., shales containing iron pyrites. 



It forms monoclinic crystals of light green colour, which 

 effloresce and oxidise when exposed to dry air, a yellowish 

 powder consisting of ferric hydrate and ferric sulphate being 

 produced. 100 parts of water dissolve 



60-9 parts of the crystallized salt at 10 

 70 ,, ,, ,, 15 



115 25 



227 ,, 46 



263 ,, 60 



333 100 



The specific gravities of solutions of ferrous sulphate solu- 

 tions vary with the strength in accordance with the following 

 table : 



Percentage of Specific gravity of 



crystallized salt. solution at 15. 



5 ... ... 1-0267 



10 ... ... 1-0537 



15 ... ... 1-0823 



20 1-1124 



