25 



as strong as possible without causing serious injury to tbe foliage. 

 Experiments have shown the average burning point to be below 

 the proportion of one pound of Paris green to one hundred and 

 fifty gallons of water. The addition of lime to the mixture is 

 recommended by some entomologists. This is thought to neu- 

 tralize the small amount of free arsenious acid in the Paris green, 

 thus preventing in some degree the danger of burning the foliage. 

 Care must be taken, however, not to add too great a quantity of 

 lime, since otherwise a more soluble compound and one of greater 

 burning powers will be formed. 



Arsenate op Lead. 



This new insecticide, which was discovered by Mr. F. C. Moul- 

 ton while experimenting under the direction of the State Board of 

 Agriculture in connection with the work of exterminating the gypsy 

 moth, has proved so far to be the best of any of the arsenical com- 

 pounds. It may be prepared by mixing approximately thirty parts 

 by weight of arsenate of soda dissolved in water and then adding 

 seventy parts acetate of lead also dissolved in water. As a result 

 of the chemical reactions which take place arsenate of lead is 

 thrown down as a finely divided white precipitate which readily 

 remains suspended in water. This poison may be purchased in 

 bulk in the market at about fifteen cents per pound. Weight for 

 weight it does not appear to be quite as effective as either London 

 purple or Paris green, but since it will not burn the most delicate 

 foliage when used at a killing strength it is pre-eminently the best 

 insecticide of the class. Notwithstanding the fact that the poison 

 has not proved all that was hoped for it when used against the 

 gypsy moth, — since a large proportion of the caterpillars of this 

 remarkably hardy insect have been known to feed unharmed on 

 foliage sprayed with great strengths of the poison, — it has proved 

 very effective against ordinary insects and its use is to be highly 

 recommended. It can be safely applied to plants either clear or 

 mixed with plaster, middlings, etc., as in the case of Paris green, 

 or used on both plants and trees as a spray when mixed with water 

 at the rate of two to four pounds to one hundred and fifty gal- 

 lons. Twenty pounds to one hundred and fifty gallons of water 

 have been used in many experiments against the gypsy moth with- 

 out apparent injury to the foliage. Another advantage of this 

 poison is that it leaves a faint white coating on the foliage, thus 

 indicating the places sprayed. I have seen trees that were sprayed 

 in June and yet showed the coating plainly in August. 



Tlie chief value of arsenate of lead, however, lies in its insolu- 

 bility in water, which obviates the danger of burning the foliage. 



