INSECTICIDES. 491 



was immersed in a solution of 2 lbs. of arsenate of lead 

 mixture, making 1 \h. of i^recipitato to 150 gal. of water. 

 Foliage uninjured. 



Xo. 11. — July 1, 1893. This experiment was similar to 

 the one preceding, except that the branch was sprayed, in- 

 stead of being immersed. A branch of a small oak tree was 

 sprayed with arsenate of lead mixture, in the proportion of 

 2 lbs. to 150 gal. of water. Foliage uninjured. 



The *' burning" effect of Paris green, when used in any 

 proportion greater than 1 lb. to 150 gal. of water, has been 

 ascribed to the presence of a small quantity of soluble 

 arsenic contained in the poison. Many chemists and ento- 

 mologists have recommended the addition of lime to the 

 mixture of Paris green and water used in spraying, in order 

 to neutralize this soluble arsenic. 'Our experiments, how- 

 ever, have tended to prove that the addition of lime is of 

 questionable value. 



In some cases we have used a considerable strength of 

 Paris green and lime without burning the foliage, while in 

 other cases a marked burning has resulted. The same vari- 

 ation in burning effects is often noticed where Paris green 

 is used alone. Vie are led to believe that the burning 

 caused by the use of Paris green and lime is dependent in a 

 great measure upon the amount of lime added, and also 

 upon the length of time the mixture is allowed to stand, 

 as our experiments have shown that, where a consider- 

 able quantity of lime is added to the Paris green mixture 

 and allowed to stand for some time, there is far greater 

 danger of l)urning the foliage than there would be from the 

 use of Paris green alone, thus apparently indicating that 

 the lime decomposes the Paris green in part, and forms a 

 more soluble compound of arsenic. 



At my request, Dr. Charles Wellington, professor of 

 chemistry at the Massachusetts Agricultural College, has 

 made a series of analyses of Paris green mixed with water 

 and of Paris green and lime mixed with water, with a view 

 of determining whether the lime would decompose the 

 arsenite of copper contained in the Paris green, and in- 

 crease the per cent, of soluble arsenic in the mixture. An 



