INSECTICIDES AND FUNGICIDES. 13 



1. The amount of polysulfide sulfur present largely governs the effectiveness of 

 the material. 



2. Thiosulfate sulfur is a product of the breaking down of polysulfide as well as 

 an original constituent of the product, and hence is present in variable amounts. 



3. The free sulfur contained is usually inert as an insecticide. It does, however, 

 have a distinct fungicidal value. (See page 26.) 



(1) Lime-stdfur. 



The efficiency of lime-sulfur-salt wash (21) for the San Jose scale appears 

 to have been first demonstrated by F. Dusey of Fresno, Cal., in 1886, 

 using a sheep dip prepared by A. T. Covell. The dip (22, 23), however, 

 seems to have been of Australian origin. About the year 1900 it began 

 to be vised in the eastern States for the control of the San Jose scale. 



The formulas adopted by different experiment stations showed ap- 

 preciable variations. A proportion of 1 pound of lime and 2-2| pounds 

 of sulfur to 1-lf gallons of water assures solution of the largest proportions 

 of lime and sulfur, the smallest amount of sludge or sediment, and a high 

 proportion of calcium polysulfide (particularly pentasulfide) with a mod- 

 erate amount of calcium thiosulfate, thus making the most efficient product 

 with the least waste. The lime must be a high-grade caustic, substantially 

 free from magnesia, which causes unnecessary loss of suKur as hydrogen 

 sulfide and increases the amount of sediment. A greater proportion of 

 lime causes the formation of more thiosulfate, and favors the formation 

 of crystals of oxysulfide. Boiling for thirty to sixty minutes with proper 

 agitation should be sufficient to dissolve all of the sulfur; longer heating is 

 detrimental. The resulting solution should be about 24° or 25° Baume. 

 A greater concentration is generally obtained at a sacrifice of thiosulfate, 

 which is converted into sulfite and free sulfur which being insoluble in- 

 crease the amount of sediment. 



The commercial product has largely superseded the home-made except, 

 possibly, in the case of orchard practice on a large scale. Lime-sulfur 

 solution appears to have been first produced commercially by the Rex 

 Spray Company (formerly Rex Stock Food Company) of Omaha, Neb., 

 as a sheep and cattle dip, which was approved by the Bureau of Animal 

 Industry Sept. 30, 1903. Later the product was tested as a spray at Cor- 

 vallis. Ore., and largely marketed as such. The commercial concentrate 

 is to-day practically standardized on a 33° Baume basis. A product of 

 greater density is more likely to crystallize on chilling. 



Concentrated lime-sulfur properly prepared is a clear orange-red solu- 

 tion with more or less sludge, depending on the purity of the lime and 

 sulfur, formula, and method of treatment. The clear solution consists 

 chiefly of so-called calcium polysulfide and calcium thiosulfate in varying 

 amounts. The sludge may contain free sulfur, together with calcium sul- 

 fite, calcium sulfate and impurities from the lime. The polysulfide is a 

 combination of lime and sulfur, approximating a ratio of 1:5, or CaSs; 

 the thiosulfate is CaSoO.. 



