588 



STATE BOARD OF AGRICULTURE. 



of oxygeu that may be used by lime-sulphur on a sprayed surface; 

 also the rapidity with which the gas might be absorbed. The lime-sul- 

 phur solution was confined on either filter paper or glass wool above 

 mercury in respiration containers — using measured amounts of air for 

 various intervals of time. By this method it was soon determined defi- 

 nitely that large amounts of oxygen were absorbed. Results of some of 

 these experiments are given in table IX. 



■ ABLE IX. 

 Absorption of oxygen by lime-sulphur. (Beaume 20.1°.) 



* This was all the oxygen in 422.6 c.c. of air. 



At the end of 

 color had dis- 

 experiment No. 



In these experiments a piece of filter paper with a measured surface 

 (both sides) was weighed dry. It was then wet with all the lime-sul- 

 phur (Beaume' 20.1°) that it would hold, after which, it became quickly 

 dried as thoroughly as possible out of doors by hot sunlight, and 

 weighed again. The difference between the latter weight and the weight 

 of the paper is recorded in the table as the amount of dry-lime sulphur 

 exposed, "^'.'hen this lime-sulphur paper had been moistened it used 

 oxygen more rapidly than when dry (compare experiments No. 4 and 

 5, Table IX). Besides, considerable oxygen was used during the pro 

 cess of drying, before the lime-sulphur w^as weighed, 

 experiment No. 1, nearly all the yellow polysulphide 

 appeared from the paper. After that, as indicated in 

 2, oxygen was used more slowly. It appeared from such experiments 

 that the polysulphides must use oxygen much more rapidly (or in greater 

 amounts) than the thiosulphate. Calcium thiosulphate was obtained 

 from Eimer and Amend and from Merck. Experiments with this com- 

 pound carried out in the manner already described for lime sulphur 

 showed that oxygen Avas used slowly. For example, 1200 sq. cm. of 

 paper surface wet with a w^iite wash of calcium thiosulphate (and used 

 wet) took up only 1.6 c. c. of oxygen in sixteen hours. The orange 

 colored lime-sulphur solution, then, is the stronger reducing agent. 

 Used in excess, it will render deep blue solutions of Indigo Carmine 

 colorless at once; and the so-called caustic action of the wash on the 

 hands seems rather due to this strong reducing power than to the al- 

 kalinty of the solution. 



Experience with P. cornutus and certain grasshoppers showed that 

 these insects could get along with very little oxygen; plant lice, it 

 had been found, used relatively much more oxygen than the larger in- 

 sects. It seemed worth while therefore, in this connection, to determine 

 how long San Jose scale insects could live without oxygen and still 

 recover. The question was tried out in the following manner : 



