124 The Spraying of Plants. 



Considerable difficulty has been experienced in mixing the 

 poison with water. Much of it floats upon the surface in the 

 form of bubbles, and it is almost impossible to wet all the poi- 

 son. When once thoroughly wet, it remains in suspension 

 fairly well. The color of the mixture is darker than that of 

 London purple. 



London Purple. The chemical composition of London pur- 

 ple is variable. Two analyses published by Bailey l are as fol- 

 lows : "1. Arsenic, 43.65 per cent; rose aniline, 12.46; lime, 

 21.82; insoluble residue, 14.57; iron oxide, 1.16; and water, 

 2.27. 2. Arsenic, 55.35 per cent; lime, 26.23; sulphuric acid, 

 .22; carbonic acid, .27; moisture, 5.29." Some samples show 

 that fully one-half of the arsenic is in a soluble condition, and 

 this easily explains the scorching of the foliage to which Lon- 

 don purple has been applied. In the manufacture of certain 

 dyes this substance appears as a waste product, which accounts 

 for the above variations. The finely divided condition of the 

 powder is one strong point in its favor. It remains sus- 

 pended in water a long time, and the liquids with which it is 

 mixed require comparatively little agitation. The value of Lon- 

 don purple does not rest in its coloring matter, for this can be 

 removed and the arsenite still be as effective as before. In 

 order to check the caustic action of the poison, it is well to add 

 an amount of lime fully equaling in weight that of the drug; 

 the dissolved arsenic will then be converted into an insoluble 

 arsenite of lime. 



The following formula indicates the manner of its use : 



London purple 1 pound. 



Lime 1 " 



Water 200-300 gallons. 



When less water is used, the amounts of the other ingredi- 

 ents should be reduced in proportion. In making applications, 

 the liquid should be stirred sufficiently to prevent the solid par- 

 ticles from settling to the bottom. 



If London purple is used without lime, foliage is commonly 

 scorched when 1 pound in 200 gallons of water is used, but more 

 dilute mixtures will prove more satisfactory. This arsenite 

 should cost from six to fifteen cents per pound. 



1 Horticulturist's Rule-Book, third edition, 2. 



