Sept. 3, 1017 



Quassia Extract as a Contact Insecticide 



507 



and the amount of extract was determined. The results are embodied 

 in Table IV. 



Table IV. — Effect of the quantity of water used on the total quantity of extract obtained 

 from 10 gm. of quassia chips macerated 24 hours 



It may be well to explain the above table with a practical example. If 

 it were desired to make a 3,000-c. c. spray solution with 10 gm. of quassia 

 chips, either of the two following methods might be used: (i) The chips 

 should be soaked for 24 hours in a small quantity of water (for example, 

 250 c. c.) , and after filtering the mixture sufficient water added to make 

 3,000 c. c; or (2) they should be soaked in the full quantity of water 

 (3,000 c. c.) for 24 hours and the mixture then filtered. From the table 

 it will be seen that in experiment i, in which 250 c. c. of water were used 

 as a solvent, 200 c. c. of filtrate yielded 0.1054 gm. of extract, while in 

 experiment 4, in which 3,000 c. c. of water were used as a solvent, 200 c. c. 

 of filtrate yielded only 0.0116 gm. of extract. However, upon diluting 

 No. I with sufficient water to make 3,000 c. c, the total extract in the 

 spray solution was 0.1317 gm., while the total extract in the 3,000 c. c. 

 No, 4 is 0.1740 gm. It is seen, therefore, that by using the entire quan- 

 tity of water to extract the chips, 32.1 per cent more extract is obtained 

 than by extracting in a small quantity of water and subsequently 

 diluting. While, of course, it is to be expected that a considerable per- 

 centage of the water-soluble extract is not quassiin, it may safely be 

 assumed that extracting with the total quantity of water assures a 

 greater percentage of quassiin in the spray solution, 



2. — EXPERIMENTAL TESTS FOR SELECTION OF EFFECTIVE FORMULAS 



In the preceding pages the quantitative determinations show the fol- 

 lowing: (i) Chips soaked for 2 hours in water yield during the first 

 extraction four times as much extract as during the second extraction; 

 but chips soaked for 24 hours yield during the first extraction six times as 

 much extract as during the second extraction. (2) Chips boiled longer 

 than four hours yield but little more extract than those boiled for this 

 period, and the quantity obtained is about one and one-half times that 



