304: Agricultural Chemistry. 



On theoretical grounds, Haywood recommends the following 

 formula for preparing, at minimum cost, a wash with the max- 

 imum amount of sulphur in solution and a moderate excess of 

 lime: 



Lime 20-22^ pounds 



Sulphur 20 pounds 



Water 50 gallons 



The mixture is best when boiled by passing steam through it. 

 Moderate slaking of the lime was found to have no influence, but 

 a comparison of flowers of sulphur and crystallized sulphur 

 showed that the crystalline form, even when finely ground, re- 

 quired much longer boiling for maximum solution and gave a 

 product of variable composition, apparently dependent on the 

 size of the particles. 



To determine what changes take place after the wash is ap- 

 plied to trees, measured quantities of the clear liquid were ab- 

 sorbed on filter papers and dried in the open air exposed to sun- 

 light. Analyses at successive stages showed the gradual oxida- 

 tion of calcium penta-sulphide into calcium thiosulphate, calcium 

 sulphite and finally calcium sulphate, with deposition of free 

 sulphur. Wetting the paper daily to simulate the daily wetting 

 of branches by dew greatly increased the rapidity of the process. 

 Indications were, that after four to six months only free sulphur 

 and calcium sulphate would be left. Haywood believes that the 

 excess of caustic lime loosens the scale insects from the tree, and 

 that the active agents in killing are sulphur in finely divided 

 form, thiosulphate, for a time, and sulphite, which is gradually 

 formed by the slow oxidations. 



Self boiled washes, in which the heat for solution is produced 

 by the chemical reaction incident to slaking the lime, are un- 

 satisfactory, even when a maximum amount of heat is so gen- 

 erated. 



Lime, sulphur, salt, soda-wash, in which caustic soda is used 

 in addition to lime, has nearly the same composition and action 

 as the simpler wash already described. It is less effective, how- 





