CATALOGUE OF INSECTS. 19 



When mixed with air-slaked lime or plaster, one part in fifty is a good 

 proportion, and it may then be very freely used. 



Spraying means the application of a watery mixture in very fine 

 particles, bj^ means of a pump, through a nozzle adapted to secure 

 this fine division of the liquid under pressure. 



Paris green is or should be insoluble in water, hence we can get at 

 best only a suspension of its particles in water. When this mixture 

 is sprayed on a plant the water evaporates and leaves a film of dry 

 green on the surface which is evenly spread in proportion to the care 

 with which the application was made, and dense in proportion to the 

 amount of poison contained in the mixture. The plant is thus really 

 coated with dry paris green and the water is used merely to facilitate 

 its even distribution. A very usual proportion is one pound of Paris 

 green in 150 gallons of water, and this, if thoroughly applied, kills 

 most of the leaf-feeding insects in their early stages and a large pro- 

 portion of them in all stages. If a stronger mixture is used, unslaked 

 lime, equal in weight to the paris green, should be added and lime 

 and green slaked together in a small quantity of water to combine 

 the free or soluble arsenious acid. 



As usually prepared, paris green is crystallized for use as a pigment 

 and, the particles being relatively large and heavy they sink rapidly 

 to the bottom in a watery mixture, which necessitates a constant 

 stirring to keep it in suspension, and makes its even application a 

 matter of some difficulty, with ordinary farm labor. 



The crystallized form, though necessary in the pigment is a positive 

 disadvantage in the insecticide, as well as an addition to the cost of 

 manufacture, hence there has been recently placed upon the market 

 an arsenite of copper or "Green Arsenoid," which, at a cost of 15 

 cts. per lb., is more effective and reliable than the ordinary run of 

 paris green. It contains about 62 % of arsenious acid and is manu- 

 factured by the Adler Color and Chemical Works, 100 William street, 

 New York. This material has the unqualified endorsement of those 

 entomologists who have experimented with it, and its advantages are 

 its more uniform strength, finer division and much lighter particles, so 

 that it remains in suspension much more easily than normal paris 

 green. It is said to be entirely harmless to foliage. This company 

 make also a pink arsenoid and a white arsenoid which are cheaper, 

 but concerning which I know too little to recommend their use. 



White arsenic is probably the cheapest form of the poison, but 

 also the most dangerous to plant life. It has been used, combined 

 with two or three times its own weight in lime to form an insoluble 

 arsenite of lime, in from 250 to 400 gallons of water, and it has been 



