﻿DEY SUBSTITUTES FOR LIQUID LIME-SULPHUR 15 



addition of sugar, at the rate of 1,11 pounds and 10 pounds to^SO 

 gallons of spray solution, does not materially reduce the effectiveness 

 against the San Jose scale. 



Experiments 6 and 7 show that dry lime-sulphur A, even when used 

 at a strength (33 pounds to 50 gallons) which furnishes an amount 

 of polysulphide sulphur equivalent to that found in standard liquid 

 lime-sulphur, can not be considered an effective remedy against this 

 scale. 



Dry lime-sulphur A, at the rate of 33 pounds to 50 gallons of water, 

 was used for experiments 7 and 8. 



After this material had been mixed a part of the solution was 

 carefully filtered to remove the insoluble portions. One-half of this 

 filtrate was used for experiment 8. Half of the insoluble sludge 

 that had been removed was added to the remaining filtrate and tms 

 was used in experiment 7. 



The 93.75 per cent control obtained with the filtered material 

 (experiment 8) compared with the 35.94 per cent control obtained 

 with the part containing the sludge (experiment 7) indicates that the 

 insoluble matter present, when this dry lime-sulphur was used at the 

 rate of 33 pounds to 50 gallons of water, greatly reduced the effective- 

 ness of the spray. 



This detrimental efi^ect of the sludge also explains why, in the 

 field experiments when the amount of dry lime-sulphur was doubled, 

 there was not a corresponding increase in effectiveness. 



The experiments with the three polysulphides, prepared to represent 

 calcium pentasulphide, tetrasulphide, and trismphide, respectively, 

 show that the pentasulphide and the tetrasulphide furnish a satisfactory 

 control of the scale and the trisulphide is of very little practical value. 

 The calcium thiosulphate, calcium sulphite, and free sulphur, at the 

 strength used, were found to be of no value. 



DISCUSSION OF RESULTS 



The foregoing experiments show that the three dry hme-sulphurs 

 tested were not staisf actory remedies against the San Jose scale, even 

 when used in excessive quantities. 



A study of the chemical analyses of the dry and hquid lime-sulphurs 

 shows the following dift'erences: 



The dry lime-sulphurs contain sulphur and calcium in the proportions 

 to form calcium trisulphide (CaSg) and calcium tetrasulphide (CaSJ, 

 they contain considerable amounts of calcium thiosulphate and free 

 sulphur, and, at increased strengths, an objectionable quantity of in- 

 soluble sludge. 



Liquid lime-sulphur contains polysulphide sulphur in such propor- 

 tions as to form calcium tetrasulphide (CaSJ and calcium penta- 

 sulphide (CaSj), with the latter predominating; very little calcium 

 thiosulphate, no free sulphur, and no insoluble sludge. 



If Shafer's theory (!2o) that the efficacy of a lime-sulphur solution 

 against scale insects is due to an oxidizing action is correct, it naturally 

 follows that the higher polysulphides (CaSj and CaSJ would be more 

 effective than the lower (CaSj) since, per molecule, they would 

 furnish a larger quantity of nascent sulphur to act as an oxidizing agent. 



The experiments given in Table 10 show that tlie calcium thio- 

 sulphate and the free sulphur are of no practical value against scale. 



