joiy »3. 1917 Toxic Values and Killing Efficiency of Arsenates 203 



arsenate and calcium arsenate were very eflfective toxic agents on the 

 first day. In regard to rapidity of action and killing efficiency, calcium 

 arsenate and acid lead arsenate were approximately the same. 



A comparison of the relative time required to kill the small larvae 

 and the nearly mature caterpillars, as indicated in Table IV, shows that 

 although there was a higher percentage of the latter dropped in the early 

 days of the test, it required a longer period to kill all of the larger forms. 



CHEMICAL ANALYSIS 



After the collection and drying of the poisoned caterpillars and excre- 

 ment from the various tests, the arsenic content was determined. The 

 method used is as follows: A counted number of caterpillars, or excre- 

 ment therefrom, were accurately weighed and introduced into a Kjeldahl 

 flask (500 c.c. capacity) together with about 15 c.c. of arsenic-free con- 

 centrated sulphuric acid. The flask was then placed over a free flame 

 and arsenic-free nitric acid added in small quantities at short intervals 

 until all of the organic matter was oxidized and the solution was per- 

 fectly clear. The solution was allowed to digest over a hot flame for an 

 hour, when all the nitric acid was expelled and white fumes of sulphuric 

 acid (H2SO4) were given off. Following the digestion, the excess of 

 sulphuric acid was driven off and the arsenic determined by titration 

 with N/joo iodin solution after reduction with potassium iodid accord- 

 ing to the modified Gooch and Browning * method. 



For convenience in making comparisons, the results of the chemical 

 analysis are calculated in milligrams contained in the amount of sample 

 taken and also the equivalent amount in i gm. of dried sample. Table 

 III gives the data obtained. 



These results throughout show consistently a higher arsenic content in 

 the tissue and a lower arsenic content in the corresponding excrement 

 with lead hydrogen arsenate as the spray than with either the basic 

 lead arsenate or calcium arsenate. Calcium arsenate comes second in 

 this comparison, while the basic lead arsenate contained the smallest 

 amount of arsenic in the tissue and shows that a large amount passed 

 through the intestinal tract unchanged, most of the arsenic eaten being 

 found in the excrement. 



A further study of the ratio of arsenic in the tissue to that contained 

 in the excrement brings out some very interesting facts. In Tables III 

 and IV we note for lead hydrogen arsenate (2 : 50) that there was found 

 0.90 mgm. of arsenic pentoxid per gram of tissue, as compared with 0.49 

 mgm. of arsenic pentoxid per gram of excrement, or a ratio of i to 0.544; 

 in the calcium arsenate (2:50) there was 0.83 mgm. per gram of tissue 



' Wh,EY, H. W., ed. OFFIQAI. AND PROVISIONAL METHODS OF ANALYSIS, ASSOOATION OF OFFIOAL AGRI- 

 CULTURAL CHEMISTS, AS COMPILED BY THE COMMITTEE ON REVISION OF METHODS. U. S. Dept. Agr. BuT. 



Chem. Bui. 107 (rev.), p. 239. 1908. Reprinted in 191a. 



