436 



AN ECONOMIC ENTOMOLOGY. 



been a tendency, therefore, to place upon tl)e market an arsenite 

 of copper whose composition is Hke that of Paris green, but 

 which, not being crystaUized is much hner, remains in suspension 

 much better and is somewhat cheaj^er. 



London purple is a waste product containing about forty-one 

 per cent, of arsenious oxide, about twenty-tive per cent, of Hme, 

 and the balance of thirty-four per cent, made up of iron, alumina, 

 dye-stuf5, etc. It is less effective than Paris green because of 

 the smaller percentage of arsenic, and more dangerous to foliage 

 because a larger proportion of it is soluble. The addition of an 

 equal weight of lime obviates the danger to plant tissue, and the 

 fine particles enable it to remain in suspension much better ; 

 hence, at one time it was considered a more desirable insecticide. 

 Unfortunately, being a waste product, it varies so greatly in com- 

 position that its use is lessening constantly in favor of the home- 

 made arsenites. 



Arsenate of lead is a combination of eleven parts of acetate of 

 lead (sugar of lead) with four parts arsenate of soda, forming an 

 insoluble compound which may be applied on foliage of any kind, 

 at any desired strength, without danger to even the most delicate 

 plant tissue. As the percentage of arsenic is very low, it requires 

 about two and one-half times as much in weight as of Paris green 

 to gain the same effect, and it is therefore much more expensive. 

 For orchard use it will hardly come into favor, except on peach ; 

 but in the garden and for use on certain shade trees it is unsur- 

 passed. It is the only combination that can be safely applied on 

 conifers, and its adhesive qualities are such as to make up in part 

 for its high price. It will be better, ordinarily, to purchase the 

 commercial preparations, whether known as arsenate of lead, 

 gypsine, or disparene; but where much is to be used, it will be 

 cheaper to buy the materials and make it up as needed, care 

 being taken to secure a good grade of acetate of lead and ar- 

 senate of soda. For a barrel of spraying mixture the following 

 will serve : 



Dissolve in one gallon of water in a wooden pail eleven ounces 

 acetate of lead (sugar of lead), and in another, in half a gallon of 

 water, four ounces arsenate of soda. Pour the arsenate solution 

 into the lead solution, stir thoroughly, and pour into the barrel, 

 which should be half full of water ; stir again, add water to till 

 up, and spray at once. The particles are very light, remain in 



