148 Accessory Wetting Substances : Paraffin Emulsions 



These surfaces were chosen to represent types that could be wetted 

 with ease, with moderate difficulty and with great difficulty. They 

 are a gooseberry leaf, a sea-kale leaf, and the white felted stage of 

 American gooseberry mildew. The gooseberry leaf is smooth without 

 being waxy and is easily wetted, the leaf of sea-kale is slightly waxy 

 and is only wetted with moderate difficulty, while the surface of 

 American gooseberry mildew offers great difficulty. 



Of the other wetting agents soap, gelatine and casein were tested. 

 Both the latter have recently been recommended, the former in an 

 acid or neutral medium, the latter in an alkahne. For both one part 

 in a thousand is relatively strong while one part in ten thousand is 

 relatively weak; they were therefore tested at those strengths. 

 Even at the weaker strength both increased the wetting power but 

 the increase was only slight. They caused complete wetting of the 

 gooseberry leaf but only raised that of the sea-kale leaf from none to 

 very slight while the effect on the mildew was nil. For waxy and 

 hairy surfaces, therefore, they are useless though they are to be re- 

 commended where extra spreading power is desired on an easily wetted 

 surface. With arsenate of lead and more especially with Bordeaux 

 mixture, where a cheap substance is required to obtain even spreading, 

 they are most efficient. 



Soap and paraffin emulsions having a soap basis may be considered 

 together as they can only be used in mixtures where soap gives no 

 chemical reaction. Where soluble salts of bases other than potassium, 

 sodium and ammonium are present insoluble stearates are formed 

 which prevent the use of soap. Half a per cent, of soap proved itself 

 slightly superior to both gelatine and casein while the higher percentages 

 gave nearly complete wetting on sea-kale and a very slight wetting on 

 the mildew. It is clear, however, that the use of soap is hmited as, 

 even at 2 % strength it proved itself inefficient when tried on the 

 most difficult surface. The paraffin emulsions proved themselves much 

 more potent. 



The strengths tried were as follows : 



Paraffin Emulsion 1, 1 



11 11 



)i )) 2, 2 



2, 1 

 In each case the figure first given is the percentage of soap and the 



