76 The Spraying of Plants. 



this purpose. In spite of this favorable report the poison was 

 not in demand, because of its caustic properties. 



After the Paris green and London purple had become well 

 known they were both considered safer insecticides than white 

 arsenic, and the first was acknowledged to be the best of the 

 three. Riley, however, did not entirely accept this opinion, but 

 thought that London purple is not more injurious upon cotton 

 foliage than Paris green is. 1 Cook was the first to make a care- 

 ful study of this point. 2 He made applications to the foliage 

 of plum, cherry, apple, pear, peach, willow, elm, and maple trees, 

 to determine the comparative degree in which the three arsen- 

 ites mentioned above are injurious. His first conclusion is as 

 follows : " London purple is more injurious to the foliage than 

 is Paris green; and white arsenic arsenious acid is more 

 harmful than is either London purple or Paris green." Later 

 experiments have confirmed this result, and the truth of its 

 general application is accepted. 



The milk of lime was first used in connection with the arsen- 

 ites to overcome their caustic properties, by Gillette, in the fall 

 of 1889. 3 The results were so encouraging that extensive ex- 

 periments were carried on the following year, and many valu- 

 able conclusions were reached in consequence of the careful and 

 extended observations made during that season. It was plainly 

 shown that " lime added to London purple or Paris green in 

 water greatly lessens the injury that these poisons would other- 

 wise do to the foliage." 4 Another interesting result obtained 

 in these experiments was that " lime added to a mixture of 

 white arsenic in water will greatly increase the injury that this 

 poison would otherwise do to foliage. If the arsenic is all in 

 solution, the lime will then lessen the injury, as in the case of 

 London purple and Paris green." 



The next step in this series of advancements was taken by 

 Kilgore. 5 During 1890 his investigations were made in lines 

 almost identical with those followed by Gillette, and many of 

 the latter's conclusions were verified. In addition to these, 



1 Kiley, U. S. Ent. Com. 1880, Bull. 8, 62. 



2 Mich. Agrie. Exp. Sta. 1889, Aug. Bull. 53. 



3 Iowa Agric. Exp. Sta. 1890, Aug. Bull. 10, 410. 

 * lUd. 419, 420. 



N. C. Auric. Exp. Sta. 1891, July, Bull. 77 b, 7. 



