BULLETIN 750, V. S. DEPARTMENT OF AGRICULTURE. 



-rale rise in temperature occurs. For instance, in 4 A the tempera 

 ture rose from 32 Q C. to 65°a, and in I- D from 32°C. to 40°<\ 



After mixing and standing for L5 to 20 minutes the precipitates 

 were filtered off, and dried over night on the steam bath. Tortious 

 were then sieved through a Nc. 100 mesh sieve, and their bulkiness 

 compared by measuring the volume occupied by 2.77 grains in a 10 

 cubic centimeter graduated cylinder. Ten times the figure read on 

 the cylinder equals the number of cubic inches per pound. The 

 measurements were taken just as the material was poured into the 

 cylinders, no attempt being made to pack it. Entomologists have 

 slated that a good calcium arsenate for dusting purposes should 

 occupy from 70 to 90 cubic inches per pound. Such determinations. 

 however, are comparable only when conducted in the same way. 



The results of these experiments are summarized in Table 2. 



Table 2. — Effect of dilution and temperature on lightness of spraying com- 

 pounds. 





Temperal 



Lime hot, 

 cold 



lire. 

 acid 



Series number, degree of dilution, and lightness of compound. 



Experi- 



A. 



B. 



C. 



D. 



ment 

 No. 



11 gm. lime — 

 :>5 cc H 2 

 10 gm. As.,0- — 

 25 cc ILO." 



Cu. in. per lb. 

 63 



11 gm. lime — 



To cc H.,0 



10 gm. As 2 3 — 



.-)(: CC ILO." 



11 gm, lime - 

 105 cc Il.,<> 

 10 gm. As 2 5 — 

 75 cc II..O." 



11 gm. lime — 

 140 cc H 2 

 10 gm. As 2 — 

 J100 cc H.,0~. 



1 



Cu. in. per lb. 

 96 



Cu. in. per lb. 

 104 



12C 



Cu. in. per lb. 

 128 



- 



Acid hot, 

 cold 



Lime 



104 



7S 



112 



■■ 



Both hot. 





63 



SO 



92 



98 



4 



Botfc cold 





104 



90 



so 



These results show thai the general tendency is the production of 

 the lighter material in the lower concentrations. But here a new 

 feature, the hardness of the lumps and the effort necessary to reduce 

 i hem to powder, makes its appearance. Amorphousness is usually 

 associated with tin production of hard, lumpy residues on drying, 

 as, lor example, in the case of aluminum hydroxid. So here we 

 have 1 I), l' ( '. and I'D. the lightest of the powders, producing hard 

 lumps, 1' I) being the hardest of the lot. It was difficult to break 

 them in the lingers, and Tor commercial use (hey would almost cer- 

 tainly have to be ground. On the other hand, t A and ID were 

 crumbly, and could be readily reduced to powder by simply shaking 

 them. Probably, then, a compromise between a method of prepara- 

 tion which produces the lightest powder ami a method which pro- 

 duces the most easily pulverized powder would be necessary. 



