These results indicate that no chemical changes occurred when calcium 

 arsenate and dry lime-sulphur were combined. The soluble-sulphur 

 compound, however, caused such a large quantity of arsenic to pass into 

 solution that would make it inadequate for utilization as a combination 

 spray. 



VALUATION OF COMMERCIAL SAMPLES 



There are at present on the market various calcium-arsenate prod- 

 ucts offered as substitutes for lead arsenate, together with the so-called 

 chemically pure salts used as reagents for chemical work. Complete 

 analyses have been made of these samples, both to ascertain whether 

 or not they approximated the theoretical composition of the pure salt 

 and also to estimate their commercial value as spray materials. Table 

 VIII gives a compilation of the results obtained. 



Table VIII. — Composition of samples of commercial calcium, arsenate 



Sample. 



Calcium 

 oxid. 



Per cent. 



Kahlbaum (C. P.) 36.62 



Baker (C. P.) 40.96 



Commercial No. i 43. 46 



Commercial No. 2 39. 20 



Commercial No. 3 ! 45. 61 



Arsenic 

 pen- 

 toxid. 



Per cent. 

 51-50 



42-75 

 40. 80 

 48.86 

 19. 22 



Calcium 

 carbon- 

 ate. 



Per cent. 



Trace. 



7-25 



40. 00 



I. 14 



8.40 



The wide variation in the composition of commercial arsenates is 

 plainly evident from the results given in Table VIII. Both Kahlbaum's 

 and J. T. Baker's chemically pure samples, supposed to be high-grade 

 salts, are mixtures of the calcium hydrogen arsenate and tricalcium 

 arsenate, with between 10 per cent and 20 per cent water of crystalliza- 

 tion or constitution. Furthermore, both the Kahlbaum and Baker 

 samples contained some calcium carbonate. Commercial samples 1,2, 

 and 3 likewise emphasize the necessity of greater care in their manu- 

 facture. Attention is especially called to sample i. It contains 40 per 

 cent of calcium carbonate, but only 43.46 per cent of total calcium, 

 estimated as calcium oxid. These figures indicate that there is insuffi- 



