Journal of Agricultural Research 



Vol. XIII, No. s 



Furthermore, the calcium carbonate prevented in no way the solubility 

 of the calcium arsenates. It is quite evident, therefore, that if there is 

 an excess of calcium hydroxid in the system, the solubility of both cal- 

 cium arsenates is inhibited. 



In order to substantiate the former results and to ascertain whether or 

 not, by allowing the action to continue for a longer time, the system 

 would come to an equilibrium and continue indefinitely with no arsenic in 

 the solution, a similar set of flasks was prepared. These were allowed to 

 stand for two weeks, with an occasional shaking, and then the supernatent 

 liquid was analyzed as before. The quantity of material used, together 

 with the results obtained, is given in Table III. 



Table III. — Effect of calchim- hydroxid on the solubility of the calcium arsenates. Time, 



tivo weeks 



Flask 

 No. 



Substances used. 



Quantity 

 added. 



Quantity 



of arsenic 



pentoxid 



found. 



Quantity 

 of calcium 

 oxid found. 



I... 

 II.. 

 III. 



rTricalcium arsenate 



\Calcium oxid 



fCalcium hydrogen arsenate 



\Calciuin oxid 



[Calcium hydrogen arsenate 

 ICalcium oxid 



Cm. 

 I. O 



•S 



I. o 



•5 



I. o 

 I. o 



Gm. 



None. 

 None. 

 None. 



Gm. 

 o. 2481 



.2451 



• 2540 



The results given in Table III further verifies those in the previous 

 experiment and emphasizes the fact that a definite point of equilibrium is 

 reached in which the concentration of calcium hydroxid in solution 

 becomes constant. Furthermore, it was found that the concentration of 

 calcium hydroxid is the same as the maximum solubility of calcium 

 hydroxid in pure water at the same temperature. 



From a practical standpoint the preventive action of calcium hydroxid 

 on the solubility of the calcium arsenates is of vital importance. The 

 free calcium hydroxid has no harmful effects upon fohage. If, therefore, 

 I part of quicklime is added for every 2 parts of either calcium hydrogen 

 arsenate or tricalcium arsenate as a combination spray, no burning of 

 foliage should result from the solubility of the arsenates. Furthermore, 

 the action under severe atmospheric conditions will be greatly diminished^ 

 since the carbon dioxid in the air will first react with the calcium hydroxid, 

 forming the harmless calcium carbonate before the calcium arsenates are 

 effected. 



ACTION OF CARBONIC ACID UPON THE CALCIUM ARSENATES 



A study of the action of carbon dioxid upon the calcium arsenates is 

 an important consideration. Although chemical changes due to car- 

 bonic acid, or a saturated water solution of carbon dioxid, as noted in 



