372 



IKON SULPHATE CHARLOCK SPRAYING 



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, FeS0 4 .7H 2 O, copperas, green vitriol. This sub- 

 stance 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. One hundred 

 parts of water dissolve 



60-9 parts of the crystallised salt at 10 

 70 15 



115 

 227 

 263 

 333 



25 



46 



60 



100 



The specific gravities of solutions of ferrous sulphate solutions 

 vary with the strength, in accordance with the following table : 



Percentage of 

 crystallised salt. 

 5 



10 



15 



20 



25 



30 



35 



40 



Specific gravity of 

 solution at 15. 

 1-0267 

 1-0537 

 1-0823 

 1-1124 

 1-1430 

 1-1738 

 1-2063 

 1-2391 



The salt is insoluble in absolute alcohol. 



Iron sulphate is used in agriculture mainly as a fungicide, occa- 

 sionally as a disinfectant, as a manure, 1 and as a veterinary medi- 

 cine. 



In recent years it has been largely employed as a means of de- 

 stroying charlock and runch, being used as a spray in the same manner 

 as copper sulphate. The strength of the solution to be employed 

 varies slightly with the age of the charlock at the time of spraying. 



If the plants be treated when young, a 10 per cent solution is 

 probably best, while for older plants a 15 per cent solution will 

 generally be advisable ; in both cases the liquid should be sprayed at 

 the rate of about 40 gallons per acre. Mixtures of the finely-divided 

 dry salt with marl, applied as a powder, have been tried, but with 

 little success. 2 As is the case with copper sulphate, iron sulphate ap- 

 pears to have a stimulating effect upon cereals, and many results, 

 among others those obtained in the experiments conducted under the 



1 Vide p. 159. 



2 Jahresbericht iiber Agricultur-Chemie, 1901, 352. 



