290 INSECTICIDES AND FUNGICIDES 



sprayings, may be useful for biting insects, sucking insects, 

 and fungi. Paris green is not satisfactory because it is 

 decomposed, freeing arsenous acid and injuring foliage. 

 Lead arsenate is the best material to use, and this in the 

 triplumbic form. The acid arsenate is not satisfactory, on 

 account of the formation of a soluble arsenic compound, 

 possibly arsenic acid. The reactions which take place when 

 lead arsenate is mixed with lime-sulphur are complex and 

 not well known. Apparently, among other compounds, lead 

 sulphide is formed, and there is an increase in the amount 

 of thiosulphate and sulphite. 



Some commercial preparations of lime-sulphur, particularly 

 the dry powders which are to be dissolved in water, consist 

 largely of sulphides of sodium or potassium. These com- 

 pounds are fungicides not contact insecticides, and, further- 

 more, their use with arsenicals causes foliage injury due to 

 a greater solution of arsenic acid. 



(d) Miscible or Soluble Oils. — Not only kerosene, but 

 crude petroleum also has valuable insecticidal properties. 

 Its use, however, like the use of kerosene in the pure state, 

 is not possible on account of its injury to trees. To facilitate 

 the proper dilution of these oils which can be so valuable, 

 the so-called miscible or soluble oils have been prepared. 



For this purpose there is made first an "emulsifier" which 

 is essentially a soft, carbolated soap, made commonly by 

 boiling 10 gallons of menhaden oil, 8 gallons of carbolic acid, 

 and 15 pounds of caustic potash, then mixing with it 2 

 gallons of kerosene and 2 gallons of -water. This emulsifier 

 is then mixed with varying amounts of other oils such as 

 crude petroleum, paraffine oil, rosin oil (Section 78, b), 

 and more kerosene. This final solution is the miscible oil 

 and when mixed slowly with water according to the spray 

 requirements forms a milky emulsion that is reasonably 

 permanent if care is used in making and mixing. 



(e) Pyrethrum, Persian Insect Powder, Buhach, is 

 made by grinding the dried flowers of various species of the 

 pyrethrum plant. The active constituent is a volatile oil of 

 strong characteristic odor which can be extracted by ether. It 

 varies in amount from 5 to 10 per cent. It is green to brown 



