INSECTICIDES AND FUNGICIDES 1007 



somewhat later than Paris green (about 1878), but is less used now than 

 formerly because of its lack of uniformity in composition and its excessive 

 burning of foliage. Its affective ingredient as an insecticide is arsenic in 

 the form of lime arsenite and lime arsenate, of which it contains about 40 

 per cent, nearly half of which is soluble. It is the soluble arsenious and 

 arsenic oxides that make this insecticide so injurious to the foliage and 

 render necessary the addition of lime. The amount of pure arsenic 

 present has been found to be about 29 per cent. For use it is customary to 

 recommend about one-quarter pound each of London purple and fresh lime 

 in from 50 to 75 gallons of water. 



White Arsenic. — The use of this poison has been recommended from 

 time to time for gnawing insects, but the time and labor required in boiling 

 it with milk of lime (thus producing an arsenite of lime) in order to avoid its 

 burning effect on foliage has prevented its general employment as an insect- 

 icide. It can be made to accomplish the same purpose as Paris green and 

 arsenate of lead, without injury to foliage, by boiling for a half hour 1 

 pound of commercial arsenic and 2 pounds of fresh lime in 4 gallons of 

 water, diluting with water finally to make 100 gallons. 



Sulphur. — Flowers of sulphur has been used for many years as an in- 

 secticide, especially for mites infesting hothouse plants. When dusted on 

 plants it does no harm to the leaves, but is not as effective as could be 

 desired. When burned in hothouses it may do severe injury to plants. 

 These defects have led to its neglect by entomologists. When sulphur is 

 boiled with lime, however, it produces a lime sulphide, in which condition 

 it becomes one of the best of insecticides for use in winter against scale 

 insects. 



Lime-sulphur Wash. — In ttiis condition thousands of barrels of the 

 boiled sulphur and lime are sold to fruit growers every year, who use it 

 largely as a remedy against San Jose scale. A concentrated solution 

 is prepared by boiling in large iron kettles, tanks or other vessels, 50 pounds 

 of fresh lime, 100 pounds of sulphur and 50 gallons of water. Part of the 

 water is heated, then the lime is added and is followed by the sulphur, the 

 whole being stirred continually while boiling, the time employed being 

 from fifty minutes to an hour. Finally, after adding enough hot water to 

 make 50 gallons, the solution is strained and set aside until ready to use. 

 Home-made solutions may not test higher than 27 to 30° Baume, but when 

 carefully made go higher and may even reach 34 or 35° Baume, the differ- 

 ences being apparently due to differences in the quality of limes used. 



The manufacturers now follow about the same formula in producing 

 their concentrated products, but because of having better facilities will 

 perhaps average higher in concentration than the fruit grower, although 

 analysis of samples bought in the market have sometimes shown that they 

 did not test as high as good home-made lime-sulphur. 



These concentrated solutions are of a deep reddish-yellow color and 

 for use must be greatly diluted with water. It is customary in spraying 



