February, ’18] 
LOVETT: CALCIUM ARSENATES 
59 
Excess Lime or Lime-Sulphur Render Materials Safe 
Considered from a practical standpoint it is evident that if some 
substance could be added to the spray which would prevent solubility 
and reactivity it would prove beneficial in the use of neutral calcium 
arsenate, Ca 3 (As 04 ) 2 , and absolutely essential if acid calcium arsenate, 
CaHAs0 4 , were to be rendered safe as a spray solution. Ordinary 
quicklime, CaO, should fulfill the requirements, the Ca(OH) 2 becoming 
soluble reacting with any arsenic going into solution forming more 
calcium arsenate. As with the previous cases this proposition was 
subjected to a variety of elaborate chemical tests and the conclusion, 
following a careful analysis of the results, is that wherever CaO is 
present in even slight excess so that Ca(OH) 2 may be found qualitatively 
in solution, no soluble arsenic will occur. One precaution must be 
observed here; be sure the lime is CaO and not CaC0 3 as this latter 
material reacts very slowly with the calcium salts and does not prevent 
the formation of soluble arsenic. If one part of CaO is added for an 
equal amount of either acid or basic calcium arsenate in the solution, 
no burning of foliage should result from the spray due to the formation 
of soluble arsenates. 
Because of the desirability of combination sprays, studies of the 
calcium arsenate-lime-sulphur mixture were undertaken. Following 
the reports of G. E. Sanders (1) as included in the proceeding of the 
Entomology Society of Nova Scotia for 1916 and in communications 
from him on the success of the calcium arsenate-lime sulphur combina¬ 
tion under field tests, more elaborate experiments with the pure mate¬ 
rials in dilute lime-sulphur solutions were conducted. 
The tests were in all cases favorable beyond expectation. In ad¬ 
dition to the pure salts, commercial calcium arsenates consisting of a 
mixture of CaHAs0 4 , Ca 3 (As0 4 ) 2 , CaC0 3 and other materials were 
tested with the lime-sulphur. With all the materials no chemical 
reaction occurred and all the constituents remained constant. These 
tests included samples of the dry lime-sulphur now on the market which 
likewise was apparently a safe combination. A careful review of the 
article by W. M. Scott (2) on arsenate of lime would indicate that 
the absence or presence of lime-sulphur in the solution was correlated 
with the presence or absence of burn. 
Analyzed for total arsenic it was found that the calcium salts contain 
more than twice as much of the active killing agent as do the corre¬ 
sponding pure lead salts. Theoretically then for spraying purposes only 
one-half as much calcium arsenate is required as of the lead arsenate. 
This point requires more elaborate experimentation. Preliminary 
laboratory tests with sprayed foliage, using a total of 50 tent caterpil¬ 
lars for each spray, indicated a very high toxicity, particularly for the 
