90 



MASS. EXPERIMENT STATION BULLETIN 210. 



The powder, therefore, was a practically pure acid calcium arsenate. 



This substance proved very soluble on standing twenty-four hours, 

 44.82 per cent of the arsenic pentoxide entering into solution. The addi- 

 tion of milk of hme to the material was therefore tried, and after 1 per 

 cent of this had been added, the amount dissolved was only .17 per cent. 

 As finally used, the spray was accordingly prepared as follows: — 



Four pounds of quicklime were slaked in about 40 gallons of water, 

 just enough water being added at a time to maintain a brisk action with- 

 out "dro-wTiing" the lime. After the slaking was completed, enough more 

 water to make 50 gallons in all was added. Eighty-five hundredths of a 

 pound of the arsenate was then mixed in, this being the amount calculated 

 as necessary to give the spray the same strength of arsenic pentoxide as 

 that of the lead arsenate sprays, in order to make the tests comparative. 

 The material was strained into the spray pump and kept well agitated. 



Commercial Calcium Arsenate. ■ — This was a bulky, white powder con- 

 sisting of minute spherical particles. It was purchased in the market, 

 and on analysis proved not to be similar to the pure material considered 

 above, but a combination of calcium and arsenic acid, with a considerable 

 excess of lime. It might, perhaps, be fairly described as a basic lime 

 arsenate. Its analysis gave — 



Per Cent. 



Water, H2O 1 . 38 



Water in combination and occluded . . . . . . .2.92 



Ferric and aluminum oxides . . . . . . . . . 1 . 30 



Calcium oxide, CaO . . . . . . . . . .45.47 



Magnesium oxide, MgO ......... -68 



Sodium oxide, NajO 1 . 09 



Arsenic pentoxide, AS2O6 . . . . . . . . .46.61 



Sulfur trioxide, SO3 18 



Chlorine, CI 02 



Soluble silica, SiOj 16 



Acid insoluble matter . . . . . . . . . . . 13 



99.94 



