ARSENATE OF LEAD. 143 



properties of arsenate of soda), he advised experimenting 

 with it. A sample was procured and was found to be entirely 

 soluble in water. When used it burned the foliage to a 

 greater extent than the other arsenical poisons. Mr. Moul- 

 ton was detailed to find some material which would precipi- 

 tate the arsenate of soda in water and thus obviate the 

 burning. He proposed acetate of lead and after several 

 experiments the desired result was obtained and the pro- 

 portions were fixed. The effect of the mixture of acetate 

 of lead with arsenate of soda in water is to throw down the 

 arsenate of lead in a fine precipitate which is held well in 

 suspension by the water and is therefore more evenly dis- 

 tributed than Paris green. 



While the complete insolubility of arsenate of lead is an 

 advantage as far as its effects on the plants are concerned, 

 it is less effective on the insect than Paris green when used 

 in equal quantities. Though the action of arsenate of lead 

 is slower than that of Paris green and London purple, this 

 may be partially accounted for by the smaller proportion 

 of arsenic in the composition. Caterpillars poisoned with 

 arsenate of lead have quite a different appearance from those 

 poisoned with Paris green. Inflammation and the shedding 

 of hair appear to be symptoms of poisoning by arsenate of 

 lead. As it is slow in its action, it is well to apply it early 

 in the life of the caterpillar or in great strength. 



The experience with arsenate of lead is in some respects 

 analogous to that with Paris green. While in-doors there is 

 no difficulty in destroying caterpillars with small quantities 

 of the poison, the effects obtained out-doors are not so satis- 

 factory. Indeed, it is only when applied at a strength of from 

 twenty-five to thirty pounds to one hundred and fifty gallons 

 of water that it appears to do exterminative work. This, to 

 some extent, may be due to the difference in the material. 

 The arsenate of lead used in the laboratory was furnished in 

 the form of a fine dry precipitate. In the field the two 

 poisons were furnished in a cruder state. They were added 

 to the water and precipitation took place in the tank. The 

 preparation ' was much less expensive when made in this 

 way but was not as finely powdered. Indeed, it required 

 considerable stirring in warm or hot water to dissolve the 



