Apr. 29, 1918 



The Calcium Arsenates 



287 



the air with the consequent formation of free arsenic acid. The tri- 

 calcium arsenate being more insoluble and more stable than the calcium 

 hydrogen arsenate would not have the tendency to react so readily and 

 the danger attending its use would be diminished accordingly. 



EFFECT OF CALCIUM HYDROXID ON SOLUBIUTY OF THE CAIyCIUM ARSE- 

 NATES 



Our investigations thus far indicate favorable possibilities for the 

 use of the calcium arsenates. The presence of any substance that 

 would prevent solubility and reactivity would prove beneficial in the use 

 of tricalcium arsenate and almost a necessity in the case of the calcium 

 hydrogen arsenate. To judge from a theoretical standpoint, ordinary 

 quicklime (CaO) would fulfill these requirements. The calcium hydroxid, 

 on becoming soluble, would react with any arsenic that goes into solution, 

 forming more calcium arsenate. 



In order to corroborate the above assumption, different amounts of the 

 pure salts were introduced into each of several 200-c. c. graduated flasks 

 together with known quantities of lime (CaO). In some cases calcium 

 carbonate (CaCOg) was also added. The flasks were then made up to 

 mark with distilled water and shaken at intervals for two days. After 

 allowing the salts to settle, determinations were made for total arsenic 

 and calcium in the clear supernatant liquid. The results are given in 

 Table II. 



Table II. 



-Effect of calcium hydroxid on ike solubility of the calcium arsenates. Time, 

 two days 



Inspection of the results given in Table II indicates that wherever 

 calcium oxid is present in even slight excess, so that calcium hydroxid 

 was found qualitatively in solution, no soluble arsenic was detected. 



