Februan-, 11] SHAFER: LIME-SULPHUR WASH 51 



phides of calcium which become oxidized on exposure to air; the 

 products of this oxidation being, at first, calcium thiosulphate and 

 free sulphur. The thiosulphate, itself, he found to be finally oxidized 

 to calcium sulphate. In order to determine whether this process of 

 oxidation might deprive a scale-insect of oxygen when treated with a 

 lime-sulphur wash, measured amounts of the spray were placed either 

 on absorbent paper or glass-wool in containers above mercury with 

 measured amounts of air. Then after various periods of time, the 

 amount of oxygen in the confined air was determined. In this way, 

 it was found that large amounts of oxygen are required to oxidize the 

 calcium polysulphides present. For example, a piece of absorbent 

 paper (10 x 12 cm.) saturated with lime-sulphur (Baume 20.1°) used 

 87.5 cc. of oxygen in sixteen and one-half hours. If the paper on which 

 the solution was placed remained moist, the polysulphides would all 

 be oxidized in a few hours. If the paper w^re quickly dried, the remain- 

 ing sulphides oxidized much more slowlj', requiring several days. The 

 thiosulphate of calcium oxidized more rapidly when kept moist than 

 when dry, but in any case, it used oxygen more slowly than the sul- 

 phides. 



It was found, moreover, that the bark of a dormant apple tree at 

 ll°to 12"^ C. was using small amounts of oxygen and giving off carbon 

 dioxide. The space beneath a scale covering on such a tree, freshly 

 sprayed with lime-sulphur, must therefore be losing its oxygen from 

 three causes — namely, the oxidation of the lime-sulphur, the respiration 

 of the bark of the tree and of the insect itself. Very few specimens 

 of San Jose scale could recover after being kept 14 hours in an atmos- 

 phere of pure nitrogen. 



It was found, also, that lime-sulphur is able to soften the wax 

 around the outer edge of the scale covering of very many of the scales. 

 The older, firmer wax did not dissolve. If the spray passed under the 

 scale covering, its presence could be detected there by the use of cor- 

 rosive sublimate which gives a black precipitate with the polysulphides 

 of calcium. If only the thiosulphate remained its presence could be 

 detected by silver nitrate with which a black precipitate results. 



When the wax, softened by lime-sulphur around the edges of the 

 scale, dries, it often sticks the scale covering so firmly to the surface 

 of the plant as to seal the insect. Sometimes the pygidium was found 

 sticking fast to the dry scale covering. In the case of Aspidiotus ficus 

 on orange, seven days after spraying, as many as 22 dead young, 9 

 living young, and 4 eggs were found sealed in beneath the shield with 

 the mother. Such confinement of course must result in the death of 

 all the family in a few days. After three to four weeks it was found 

 that in many cases, the oxidized salts in the wax of the scale stooled 



