Apr. 29. i9i8 The Calcium Arsenates 285 



time. It was finally brought upon a Buchner filter and washed free 

 of chlorids with hot water. After drying in an oven at 100°, the 

 analysis gave the following results : 



Total 

 percentage. 



Calcium as CaO 38. 49 



Arsenic as AS2O5 52. 50 



These results indicate that a salt is produced containing two molecules 

 of water of crystallization and agreeing with the formula Ca3(As04)3 . 2H2O 



When further dried at 175°, the pure calcium arsenate was obtained 

 as shown by the following analytical data: 



Total 

 By analysis: percentage. 



Calcium as CaO 42. 16 



Arsenic as AS2O5 57-73 



Tlieoretical composition of Caj (As04)2: 



Calcium as CaO 42. 20 



Arsenic as AsjOg 57- So 



SPECIFIC GRAVITY, SOLUBILITY, AND RELATIVE STABILITY OF CALCIUM 

 HYDROGEN ARSENATE AND TRICALCIUM ARSENATE 



A spray material in powder form must be in a fine state of subdi- 

 vision to facilitate efficient spreading on foliage and must have a specific 

 gravity sufficiently low that it will remain in suspension in water for a 

 considerable length of time. 



The specific gravity was obtained by determining the weight of 

 absolute alcohol displaced by a known quantity of the salt. The alcohol 

 was specially prepared by redistilling the commercial chemically pure 

 absolute alcohol over calcium oxid obtained by igniting chemically 

 pure calcium carbonate (CaCOg). All weighings were made at 20° C. 

 with recently standardized weights. The specific gravity for the differ- 

 ent salts was found to be as follows : 



Calcium hydrogen arsenate (CaHAs04 . HjO) at 20° j 4° 3. 09 



Anhydrous calcium hydrogen arsenate (CaHAs04) at 2o°/4° 3. 48 



Tricalcium arsenate [Caj (As04)2. H2O] at 20° 1 4° 3. 23 



Anhydrous tricalcium arsenate [Cag (As04)2] at 20° 1 4° 3. 31 



The solubility of an arsenical utilized for insecticidal purposes is an 

 exceedingly important factor. The presence of an excess of soluble 

 arsenic or any salt that would ultimately pass into solution, forming 

 arsenic acid or a soluble arsenate, would cause burning of foliage and 

 render the arsenical useless for spraying purposes. Qualitative tests 

 showed that both calcium hydrogen arsenate and tricalcium arsenate 

 were slightly soluble, and, like many other calcium salts, the solubiUty 

 is greater at lower than at higher temperatures. The determinations 

 were made at 25° C. in a constant-temperature bath that was fitted 

 with a revolving bottle holder. By means of the latter, four bottles 

 could be submerged and kept in a state of constant agitation during the 



