Arsenicals 337 



with lead, lime or other substance that produces a com- 

 pound insoluble in water. 



White arsenic is the cheapest form in which arsenic can be 

 obtained. It is a white powder, soluble in water, and very injurious 

 to foliage. A cheap and efficient insecticide may be prepared from 

 it as follows: 



For use with bordeaux mixture only. Sal-soda, two pounds; 

 water, one gallon; arsenic, one pound. Mix the white arsenic into 

 a paste and then add the sal-soda and water, and boil until dis- 

 solved. Add water to replace any that has boiled away, so that 

 one gallon of stock solution is the result. Use one quart of this 

 stock solution to fifty gallons of bordeaux mixture for fruit trees. 

 Make sure that there is enough lime in the mixture to prevent the 

 caustic action of the arsenic. 



For use without bordeaux mixture. Sal-soda, one pound; water, 

 one gallon; white arsenic, one pound; quicklime, two pounds. Dis- 

 solve the white arsenic with the water and sal-soda as above, and 

 use this solution while hot to slake the two pounds of lime. Add 

 enough water to make two gallons. Use two quarts of this stock 

 solution in fifty gallons of water. 



As there is always some danger of foliage-injury from the use 

 of these home-made arsenic compounds, and as they cannot be 

 safely combined with the dilute lime-sulfur when used as a summer 

 spray, they are now rarely employed in commercial orchard spraying. 



Arsenate of lead was first used as an insecticide in 1893, in Massa- 

 chusetts. For orchard work throughout the country, it has now 

 almost entirely replaced paris green. It adheres better to the leaves, 

 may be used at considerably greater strength without injuring 

 the foliage, and may be combined with a dilute lime-sulfur solu- 

 tion or with the self-boiled lime-sulfur. Chemically, arsenate of 

 lead may be either triplumbic arsenate or plumbic-hydrogen arsenate. 

 The commercial product usually consists of a mixture of these two 

 forms, the proportion depending on the method of manufacture 

 employed. It is usually sold in the form of a thick paste, but for 

 some purposes the powdered form is preferred. Under the National 

 Insecticide Law of 1910, arsenate of lead paste must not contain 

 more than 50 per cent water and must contain the arsenic equivalent 

 of at least 12 Y^ per cent arsenious oxid. The water-soluble arsenic 

 must not exceed an equivalent of three-fourths of 1 per cent of 

 V 



