﻿16 BULLETIN 1371^ TJ. S. DEPARTMENT OF AGEICULTTTEE 



Experimeiits 6 and 7 in Table 10 show that the presence of a consid- 

 erable amount of insoluble sludge greatly reduces the effectiveness of 

 these dry preparations. It is thus clearly evident that there are 

 adequate chemical and physical reasons for the failure of these dry 

 lime-sulphurs to control the San Jose scale. 



SUMMARY 



(1) The dry lime-sulphurs used were found to be of little practical 

 value against the San Jose scale. 



(2) The addition of sugar did not materially reduce the effective- 

 ness of liquid lime-sulphur. 



(3) Calcium polysulphides corresponding to the pentasulphide and 

 tetrasulphide were found to be effective and that correspondmg to the 

 trisulphide of very little value against the San Jose scale. 



(4) Calcium thiosulphate, calcium sulphite, and free sulphur were of 

 no practical value. 



(5) The lack of effectiveness in the dry lime-sulphurs may have been 

 caused by the following: 



{a) When the water is removed from liquid lime-sulphur to produce 

 the dry calcium-sulphur, the calcium polysulphides are changed from 

 the mixture of polysulphides 5 (CaSj) and 4 (CaSJ with the 5 pre- 

 dominating, which is found in liquid lime-sulphur, to a mixture of 

 polysulphides 4 (CaSJ and 3 (CaSg) in approximately equal proportions. 

 This change would, according to the experiments given in Table 10, 

 reduce the effectiveness of the dry calcium sulphurs since the higher 

 polysulphides were found to be more effective than the lower ones. 



(b) The calcium thiosulphate, sulphite, and free sulphur present are 

 not effective. 



(c) The presence of a considerable amount of insoluble sludge 

 apparently reduces the effectiveness of these materials against the 

 San Jose scale. 



DRY SODIUM-SULPHUR COMPOUNDS 



The dry sodium-sulphur compounds, which are also sold as sub- 

 stitutes for lime-sulphur solution, are likewise of comparatively 

 recent development. Patents ^^ covering several methods for the 

 manufacture of these preparations have been obtained. However, 

 the method most generally employed consists in heating or fusing 

 together sulphur and sodium carbonate (soda ash), or sulphur and 

 caustic soda. 



CHEMICAL COMPOSITION 



The results of the chemical analysis of 15 samples of sodium- 

 sulphur compounds, obtained in the open market and including the 

 principal brands, are given in Table 11. 



" United States Nos. 1,044,452; 1,132,476; and 1,457,652. 



