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INSECTICIDES. 



By H. M. LEFROY. 



{Imperial College of Science, South Kensington.) 



It would be interesting to collect information as to the insecticides 

 in general use in horticulture in different countries in any one season 

 and to determine as far as possible what were the circumstances leading 

 to their use. There is, I believe, a fashion in insecticides : at one time 

 Paris Green and London Purple ruled; then came Lead Arseniate in 

 America ; this is apparently giving place to Zinc Arseniate and Barium 

 Arseniate, while there is reason to hope that Lead Arseniate, and 

 perhaps Lead Chromate, will be more familiar in this country. 



So, too, for contact poisons. I remember the era in America of 

 paraffin emulsions and rosin washes; then came whale oil soap; lime 

 salt and sulphur followed, then the heavy oils and then "miscible 

 oils." The vogue of the lysol and similar mixtures on the Continent 

 has to be noted, and we may note that miscible oils are being used 

 more freely in Australia and South Africa. 



In estimating the causes of these successive fashions one would 

 need to distinguish the effect of the recommendations of State Depart- 

 ments of Entomology and the influence, increasing in recent years, of 

 the weight of pure advertising by firms interested in the sale of the 

 particular products they were able to handle. In this paper I omit 

 entirely the "patent" or "proprietary" insecticides in so large use, 

 since it is not always clear on what ingredients their action depends, 

 and I confine myself to insecticides of definite known constitution, or 

 those which depend upon the presence of some known chemical com- 

 pound. 



It is not easy to ascertain exactly what insecticides are at present 

 used on a large scale in this country, but I have tried to do so from three 

 sources: the first is the published recommendations of horticultural 

 journals; the second is the recommendations in the leaflets of the 

 Board of Agriculture; the third is those that I gather from general 



