J. Y. Eyre axd El. 8. Salmon 505 



A comparison of the results of our experiments makes it clear that 

 the proportion of "sulphide-sulphur" present is no index of the efficacy 

 of a sprtiy-fluicP. It will be seen that a solution of yellow ammonium 

 sulphide containing 0-13 % sulphide-sulphur is invariably fungicidal, 

 whereas a solution containing ()-13 % sulphide-sulphur in the case 

 of "liver-of-sulphur" has no fungicidal value — the concentration at 

 which the latter substance becomes fungicidal is 0-34 % sulphide- 

 sulphur. 



Further, solutions containing as much as 1-6 % and 3-3 % sulphide- 

 sulphur in the case of a colourless solution of ammonium hydrosulphide 

 and a colourless solution of ammonium sulphide respectively failed 

 to do more than check the fungus temporarily. 



It seems evident, therefore, that the soluble polysulphides present 

 are the substances of fungicidal value. The question which then arises 

 is whether the property of killing the fungus is due to the direct action 

 of the polysulphides themselves or whether it is due to the sulphur 

 which is deposited when these compounds decompose. 



With the object of gaining information on this point determinations 

 have been made of the amount of sulphur which is deposited from a 

 solution of colourless ammonium hydrosulphide and from a solution 

 of yellow ammonium sulphide when exposed to air under conditions 

 similar to those obtaining when these substances are used as spray- 

 fluids. 



Definite quantities of these solutions were absorbed on tared filter- 

 papers and allowed to dry in the air alongside similar filter-papers 

 which served as controls and as counterpoises in weighing. The solution 

 of ammonium hydrosulphide used contained 5-93 % of "sidphide- 

 sulphur" (somewhat less than the stock solution used in Exper. 2, i.e. 

 6-7 %) and it was found to deposit 0-356 grm. per 100 c.c. of solution. 

 The solution of yellow ammonium sulphide contained 2-19 % of 

 "sulphide-sulphur" (the stock solution from which the spi-ay-flvrids 

 have been prepared) and, in this case, the deposit of sulphur amounted 

 to 2-56 grms. per 100 c.c. of solution. 



From these estimations it is calculated that when the above- 

 mentioned solutions are diluted in the manner followed when preparing 

 such solutions for spraying purposes 100 c.c. of the ammonium hydro- 

 sulphide spray-fluid (containing in this case 2-96% sulphide-sulphur: 



^ In an article in the Joiirn. Board of Agric. 1914, vol. xxi. p. 236, giving the analyses 

 of variou.s commercial samples of "liver-of sulphur," the assumption has been made that 

 the fungicidal value of any sample is determined by its sulphide-sulphur content. 



