466 JOURNAL OF ECONOMIC ENTOMOLOGY [Vol. 7 



sulfide" (for explanation of this term see bulletin referred to) sulfur 

 may be used in estimating the amount of oxygen which will combine 

 with the polysulfide present to form thiosulfate. In this case, 1 cc. 

 of tenth-normal iodine is equal to 0.0024 grams of oxygen. The 

 writer suggests that this oxygen-consuming capacity might be expressed 

 as the "oxygen number" (analogous to the iodine number of fats), 

 this term meaning the amount of oxygen consumed expressed as per 

 cent of the lime-sulfur solution, or, in other words, the number grams 

 of oxygen absorbed by 100 grams of lime-sulfur. 



Free sulfur is Uberated from lime-sulfur by reactions represented by 

 the following equations: 



CaS4+3 = CaS203+2S 

 CaS5+3 = CaS203+3S 

 CaSaOg =CaS03+S 



Since the oxidation of the polysulfide takes place rapidly there is a 

 correspondingly rapid deposition of sulfur. The liberation of sulfur 

 due to the decomposition of the thiosulfate is much less rapid. Con- 

 sidering everything, however, it appears that all of the sulfur liberated 

 might be of equal insecticidal value; at least, there is no good evidence 

 available to the contrary. The chemical estimation of the sulfur which 

 will be deposited from a given amount of lime-sulfur solution can be 

 made without difficulty. All of the sulfur present in the polysulfides 

 in excess of that necessary to form the "monosulfide" of calcium com- 

 bined in this form, would be deposited; also one half of the sulfur 

 present as thiosulfate in the original solution. The chemical methods 

 for making these determinations have already been worked out in a 

 thorough manner^ and it is unnecessary to go into a detailed discussion 

 of them here. The author suggests that the total free sulfur which 

 would be deposited might be expressed as the ''available sulfur number," 

 this term meaning sulfur deposited expressed as per cent of the original 

 lime-sulfur solution. 



The third insecticidal property mentioned above is not so easily 

 estimated. In fact, it is not definitely known why the spray solution 

 softens the wax on scale insects. It might be stated, however, that 

 calcium thiosulfate is neutral in solution and gives no caustic effect on 

 the hands, while solutions containing calcium polysulfide are 'very 

 caustic. It is true that there is a small amount of calcium hydroxide 

 in lime-sulfur solutions, due to hydrolysis of the polysulfide, but it is 

 present in insufficient quantity to say that the caustic properties are 



I Jour. Amer. Chem. Soc. 27, 244 (1905). 

 Jour. Ind. Eng. Chem. 2, 271 (1910). 

 Tech. BuU. No. 6, Mich. Agr. Exp. Sta. 



