170 INTERNATIONAL CONGRESS OF VITICULTURE 



preparations, the polysulphides are the most active fungicidal ingredients. 

 They are likewise the most caustic. Foliage injury sometimes obtained by 

 the use of these materials may in all probability be attributed to the poiy- 

 sulphides. 



The ingredients of second importance as fungicides are the thiosulphates. 

 Thiosulphates in general have a definite fungicidal value. They are less 

 active, however, than the polysulphides and their causticity is almost 

 negligible. 



DECOMPOSITION OF SULPHIDES AND THIOSULPHATES AFTER 

 APPLICATION TO FOLIAGE. 



A knowledge of the decomposition products of the foregoing materials 

 after application may be of value in deciding the suitability of these materials 

 for the various uses to which they may be applied. Haywoodi has investi- 

 gated this point in reference to the decomposition products of lime sulphur. 

 His experiments indicate that calcium polysulphides are oxidized to thio- 

 sulphates by the action of the air and that the thiosulphates thus produced 

 and those originally present in the wash are further oxidized to sulphites, 

 and that the sulphites are eventually still further oxidized to sulphates. The 

 first two oxidations liberate sulphur in a very finely divided condition. The 

 experiments were made under laboratory conditions and may not show the 

 precise reactions that occur under field conditions. From the data secured 

 in these experiments, it was calculated that it would take about four or five 

 months for a complete oxidation of the wash and it was also shown that the 

 rate of decomposition was very much increased by wetting the material 

 every day simulating the effect of dew. No reference is at hand giving 

 similar experimental data on the alkali sulphides. From a consideration of 

 their chemistry and the miscellaneous facts known about such compounds 

 it seems reasonable to conclude that their decomposition would be in a 

 manner analagous to that of lime sulphur given above; that is, the poly- 

 sulphides and thiosulphide would be slowly oxidized to sulphites and eventu- 

 ally to sulphates with the liberation of free sulphur during the whole process 

 with the exception of the last stage, the chief difference in the final product 

 being that lime-sulphur solution is finally oxidized into insoluble calcium 

 sulphite and calcium sulphate whereas all of the decomposition products of 

 alkali sulphides are readily soluble in water. It may be well to point out 

 here one advantage in the use of lime sulphur as a spray of general utility. 

 The final decomposition product to which is converted all of the ingredients 

 of lime sulphur is calcium sulphate or gypsum. This material is a natural 

 constituent of many soils, is applied in many cases for the improvement of 

 soils and in no case is it a detriment and in some cases it may be a benefit. 

 This consideration, however, may not be of great significance for the reason 

 that the decomposition products are in such small amount that their effect 

 upon the soil is negligible. There is this thought, however, that the continual 

 application of lime sulphur every year and over an indefinite period of years 

 can not in any possible way add a trace of undesirable material to the soil. 

 The decomposition products of the alkali sulphides, however, are readily 



i Haywood, J. K., "The Lime-sulphur-salt Wash and Its Substitutes," 

 U. S. D. A. Bureau of Chemistry Bui. 101 (1907). 



