50-i Fumiiciddl l^inpcrfii's of ('crtdin Sjjnii/-/'itii<ls 



Theoretical Considerations. 



Althouiih a coiisiclL'rable literature is to he found (le;iiin<r with 

 alkaline sprays — particularly those known as "linie-sul])hur" and 

 "liver-of-sulphur"— there apjjears to be little of a definite character 

 known indicating which of the several constituents of these mixtures 

 possess the fungicidal properties associated with these spray-fluids. 



A consideration of the results obtained in our experiments makes 

 it evident that certain of the views referred to above (p. 475) are 

 erroiuMuisIv founded, although sufficient data have not yet been 

 obtained on which to base a full discussion of the problem. 



It has been claimed that solutioi\s of "liver-of-sulphur"' are fungicidal 

 mainly by reason of' the free alkali they contain initially or by reason 

 of that which may become available subse(|uent to spraying. That 

 this explanation does not hold good appears clear from the following 

 evidence based on results obtained in our experiments with solutions 

 of caustic soda and of a solution of "liver-of-sulphur"' which is fungicidal. 

 Accepting a 1 % solution of the sample of "liver-of-sulphur" used in 

 our experiments as being definitely fungicidal, calculation shows that 

 this cannot contain more free alkali than the e(|uivalent of O-l % NaOH, 

 whereas a solution containing 0-5 % NaOIl proved to be not fungicidal. 

 Thus it seems clear that a concentration of "liver-of-sulphur"' which is 

 entirely fungicidal will not contain at any time a sufficient concentration 

 of free alkali to destroy the mildew. 



Equallv clear evidence of the inefficacy of free alkali has been found 

 in the case of vcllow anunoiniini snlpliiiic. Solutions of this compound 

 which cannot, by rea.son of their mode of preparation, contain as much 

 as 0-4 % total ammonia are found to be fatal to the mildew (ciik 

 Yellow Ammonium Sulphide. Hxpers. !i. lit and 11); whereas our 

 experiments with solutions of ammonia show that this alkali u]i 

 to 2 °,, concentration is not detrimental to the fungus. 



Till' negative results obtained in our experiments with solutions 

 of sodium carbonate also give the same evidence that the weak alkaline 

 nature of the spray-fluid is not responsible for fungicidal action. 



In view of the fact that the ammonium sulphide solution used^ 

 which proved so efficacious — -contained no sulphate and onlv indetermin- 

 ablv snuill quantities of thiosulphate and of sulphite, this discounts 

 verv hirgelv the suggestion that aiiv of these substances are responsible 

 for the fungicidal action oliserxcd. Tt was not surprising therefore to 

 find that sodium thiosuljihate exhibited no fungicidal pro])erties. 



