194 



JOURNAL OF ECONOMIC ENTOMOLOGY 



[Vol. 8 



this year by the gipsy moth. There has been shght injury in previous 

 years but the damage was serious in several cases this season. 



Peesident H. T. Fernald: The next paper on the program is 

 by W. M. Scott. 



ARSENATE OF LIME OR CALCIUM ARSENATE 



By W. M. vScoTT, Baltimore, Md. 



The possibihty of Combining arsenic with a cheaper base than lead 

 to produce a safe and effective insecticide for use on fruit and shade 

 trees has no doubt occurred to nearly every economic entomologist. 

 Calcium is the cheapest material that could be used for this purpose 

 and calcium arsenite or arsenite of lime has been recognized as an 

 insecticide for a number of years, but omng to its injurious effect on 

 vegetation it never has and probably never ^\dll come into general use. 



Arsenate of lime, however, is a more stable and less soluble compound 

 and should, therefore, be less caustic in its effect on fruit and foliage. 

 So far as the writer is aware arsenate of lime is not known in ento- 

 mological literature and has never been given much consideration. 

 I am informed by Prof. A. L. Quaintance of the United States Bureau 

 of Entomology, that during the past three years his office has conducted 

 spraying experiments with this material and that the results have 

 been uniformly good, although no account of the work has yet been 

 published. For the past two years the writer has endeavored to 

 determine the value of arsenate of lime as a substitute for arsenate of 

 lead and the results obtained at least indicate that this material is 

 worthy of further investigation. 



Arsenate of lime may be prepared as a monocalcium, dicalcium or 

 tricalcium arsenate. On the dry basis tricalcium arsenate (Cas 

 (As204)2) contains, theoretically, 42.2 per cent lime (CaO) and 57.8 per 

 cent arsenic oxide (AS2O5). The material used in the writer's experi- 

 ments contained 46.8 per cent lime and 47.8 per cent arsenic oxide on the 

 dry basis, and therefore had 11 per cent more lime than would occur 

 in the true tricalcium arsenate. It contained less than 0.05 per cent 

 soluble arsenic oxide. On the basis of 50 per cent of water this mate- 

 rial would contain 23.9 per cent arsenic oxide, but in preparing the 

 paste the water content cannot well be reduced below 60 per cent 

 without the use of a filter press. 



In the experiments recorded herein the paste was prepared to con- 

 tain the same percentage of arsenic oxide as is found in standard 

 arsenate of lead, i.e., from 15 to 16 per cent. The rate of dilution 

 for both materials was 2 pounds to 50 gallons of water which gave 

 the same arsenic content in both kinds of diluted sprays. 



