Volume III APRIL, 1917 No. 4 



ACCESSORY WETTING SUBSTANCES WITH SPECIAL 

 REFERENCE TO PARAFFIN EMULSIONS. 



By a. H. lees, M.A., 



Plant Pathologist, University of Bristol, Agricultural 

 and Horticultural Station. 



Within the last three years or so the opinion has been gradually 

 gaining ground that one of the most important points in a spray fluid 

 whether for fungicidal or insecticidal purposes is its wetting power. 

 The author's attention was first called to this point when using certain 

 proprietory insecticides which, used according to the directions given, 

 were not very effective but which, on addition of soft soap, had their 

 wetting powers and therefore their killing powers greatly increased. 

 Reference was made to this subject in the Annual Report for 1913 of 

 the Research Station, Long Ashton^, and since that time other papers 

 have appeared dealing more fully with the physical problems involved 

 in the question^'^. It is not proposed here to touch this side of the 

 problem as the author is not a physicist but to give certain results 

 bearing more on the immediately practical aspects of spraying. 



It has long been known that the addition of soft soap to a fluid 

 containing no substance capable of precipitating soap, causes an in- 

 crease of wetting power. No quantity of soap, however, has proved 

 sufficient to wet such resistant insects as the colonies of Woolly Aphis 

 which occur on apple trees. These insects excrete a covering of waxy 

 threads on their back ^vhich render them impervious to ordinary spray 

 fluids. The same difficulty was found in the experiments of Prof. 

 Barker and the author against American Gooseberry Mildew. There 

 was therefore a real need to find a satisfactory accessory wetting agent. 



^ The Annual Report of the Agric. and Hart. Research Sta., Long Afhton, Bristol, p. 70. 



^ Lefroy, " Insecticides." Ann. App. Biol. Jan. 1915. 



^ W. F. Cooper and W. H. Nuttall, "The Theory of Wetting and the Determination of 

 the Wetting Power of Dipping and Spraying Fluids containing a Soap Basis." Journ. 

 Agric. Sci. Vol. vn, pt. 2, Sept. 1015. 



Ann. Biol, in 10 



