REPORT OF THE SOCIETY . 13 



arsenic, were soon found to be unsatisfactory on account of their liability to 

 burn foliage unless great care were taken to neutralize the free acid present. 



Arsenate of Lead. — In 1892. Arsenate of Lead was first emploj-ed against the 

 Gypsy moth, and gradually gained favor as a substitute for Paris Green. It 

 has the advantage of being harmless to foliage, of remaining well in suspension 

 without constant stirring, and of sticking to the foliage for a long time. It can, 

 moreover, be used with Bordeaux and lime-sulphur as a combination spray. 

 As the paste form deteriorates on exposure, while the powder is quite stable, the 

 latter is recommended for general use. 



Sanders and Kelsall, of the Dominion Entomological Laboratory, Annapolis, 

 Nova Scotia, have done some admirable work on the reactions that occur when 

 arsenate of lead is mixed with other chemicals. For example, they found that 

 apple foliage is liable to be injured when more than 15 mgms. of AS2O5 are in 

 solution per 1000 cc. of water. In the case of lead arsenate (PbH AsO^) it is 

 seldom soluble to the extent of 4 mgms. of AsoO., in 1000 cc, and on the average 

 about 2 mgms. However, when the manufacturer adds a small amount of MgO 

 to make it float better in water, a chemical reaction occurs which makes it dan- 

 gerous to leaves. ]\Iagnesium arsenate (]Mg H ASO4) is formed, which dissolves 

 to such an extent in water that 40 or 50 mgms. of As2 O5 are to be found in 

 1000 cc. of water. 



Again, when a very small quantity of lime is added to lead arsenate, a lime 

 arsenate (Ca H ASO4 is formed which is highly dangerous. But if the lime be 

 present in large quantities Caa (AsO^) is formed which is not dangerous. 



Arsenate of Lime. — During the last two or three years, arsenate of lime has 

 been employed by many growers as a substitute for the lead arsenates, on the 

 score of reduced price and higher poison content, pound for pound. It is, howe- 

 ver, less stable, but with the addition of a stabilizer such as hydrate of lime, 

 Bordeaux, lime-sulphur, or soluble sulphur, when excess lime is present, it is 

 quite safe to foliage. 



For the coming year arsenate of lime is being widelj^ recommended as a 

 cheap and effective substitute for arsenate of lead. 



Lime-Sulphur. — Perhaps the most outstanding achievement in commercial 

 spraying during the last forty 3'ears has been the introduction and improvement 

 of lime-sulphur. In the eighties the California fruit growers used it against 

 both the scale and the peach leaf curl. As an insecticide against scale and many 

 sucking insects, it has been employed ever since, but, bj- the early method of 

 preparation, it had to be applied warm for crystals soon formed, which tended to 



