276 Insecticides from a Chemical Stand^mlnt 



be thereby retained, whilst the injurious effect on the host might be 

 diminished. We are not aware that any organic arsenic compound 

 has been employed in this connection, the principal reason being, 

 possibly, that such compounds are usually too expensive for the purpose ; 

 but the use of an interesting organic compound of copper has been 

 suggested. This is cupric-di-methanal-di-sulphite (Cu(H2C. OH. 803)3), 

 which is easily prepared by passing sulphur di- oxide into a suspension of 

 copper hydroxide in 40 % formalin. A clear blue solution, containing 

 3 % of copper is thus obtained, which, it is claimed, combines in itself 

 a copper insecticide and a sulphuring agent. 



The high insecticidal value of emulsions of paraffin or other oils 

 has long been recognised, whilst copper, in one form or another, is 

 in very general use as an insecticide and fungicide. Is it possible 

 to combine the advantages of both? Copper resinate is soluble in 

 mineral oils, so that by emulsifying such a solution of copper resinate, 

 a preparation would be obtained, which might possess the insecticidal 

 properties of both an oil emulsion and of copper. 



According to Pickering, the action of Bordeaux Mixture is due to 

 the gradual liberation, by the atmospheric carbon-dioxide, of small 

 quantities of soluble copper sulphate. It is a well-known fact that 

 certain substances are much more reactive when freshly liberated from 

 their compounds.- In many cases this is due to their "nascent state"; 

 in others, the extremely fine state of division, in which they are 

 deposited, is doubtless responsible for their increased activity. Atmo- 

 spheric carbon dioxide might be employed with the greatest advantage 

 in the precipitation of insecticidal compounds in this super-active form, 

 but, with the exception of Bordeaux Mixture, and possibly potassium 

 sulphide, little, if any, use of it has been made up to the present. Let 

 us consider, for example, ^-naphthol. This is a constituent of coal- 

 tar; it has high bactericidal properties, and, being a phenol, presumably 

 would act as an insecticide. It is a simple matter to prepare a solution 

 of ^-naphthol in caustic soda, so adjusted that a mere trace of carbon 

 dioxide would precipitate a minute quantity of the ^-naphthol. Such 

 a solution used as a tree spray might prove to be of the greatest value, 

 because its active constituent would be liberated gradually, and so 

 could only act upon the foliage in extremely minute quantities. 



To take another example: preparations containing potassium 

 sulphide (liver of sulphur) are largely used as insecticides. To what 

 particular property these owe their insecticidal action is apparently 

 doubtful. The gradual precipitation of sulphur from the admixed 



