286 



Journal of Agricultural Research 



Vol. XIII, No. s 



entire experiment. Various amounts of the samples were introduced 

 into the different bottles, and 300 c. c. of conductivity water were added 

 to each. They were then placed in the constant-temperature bath and 

 allov/ed to revolve for five days, when 100 c. c. were removed from each 

 bottle and evaporated on a steam bath. The. bottles were replaced in 

 the bath and allowed to continue three days longer, when another 100 

 c. c. was removed and evaporated as before. 



Finally, after evaporation the salts were dried in an electric oven at 

 100° C. and then at 175°, as recorded in Table I. 



Table I. — Comparative solubility at 25 °C. 0/ calcium hydrogen arsenate and tricalcium 



arsenate 



Salt. 



Calcium hydrogen arsenate 

 Do 



Tricalcium arsenate 



Do 



Drying L height 

 t^^e- ^ter). 



°C. 



100 



100 



175 



o. 3308 



.3108 



. 0140 



Analysis of the dissolved material showed that the composition of the 

 latter was the same as that of the original salt used, indicating no per- 

 ceptible hydrolysis. 



We observe from the results given in Table I that at 25° C. the calcium 

 hydrogen arsenate is far more soluble than the tricalcium arsenate. This 

 point is of considerable practical importance, since the solubility of the 

 calcium hydrogen arsenate proximates the amount shown by field 

 experiments to cause burning of foliage. These data indicate the futility 

 of attempting to use the pure calcium hydrogen arsenate alone as a spray. 

 The tricalcium arsenate, on the other hand, is only slightly soluble, and 

 the danger of burning from that source would probably be negligible. 



From the standpoint of densit)^ and solubility, it is probable that the 

 tricalcium arsenate could be safely used as a spray material, while the 

 calcium hydrogen arsenate is doubtful. An important factor remains 

 yet to be taken into consideration, namely, the stability of the salts. 

 This was ascertained by a study of the chemical change that resulted 

 when either the calcium hydrogen arsenate or tricalcium arsenate was 

 shaken at intervals for several days in solutions of acids, both organic and 

 inorganic, ammonium hydroxid, sodium hydroxid, sodium chlorid, and 

 similar salts. In all cases tried the calcium hydrogen arsenate reacted, 

 dissolved, or arsenic in soluble form was found in solution. However, 

 the tricalcium arsenate manifested greater stability and in many instances 

 showed only slight reactivity. Inferring from the relative stability of 

 the two salts, both arsenates would under severe and abnormal climatic 

 conditions probably yield to the action of carbon dioxid and moisture in 



