A. H. Lees 143 



t[uoted by Pickering in which the amount of soap was stated, in 7 it is 

 •5 % or lower. In these 7 therefore, supposing hard water had been 

 used, however httle paraffin were added, scorching would be probable. 

 In the others where the paraffin content was relatively high and the 

 soap content relatively low there would also be a hkehhood of scorching 

 since, as will be shown later, the amount of paraffin that can be 

 held in stable emulsion depends largely on the amount of soap 

 present. 



Prehminary experiments had shown that it is possible to obtain 

 wetting from paraffin emulsions in two ways. If the ratio paraffin 

 to soap was low, wetting, if it occurred, was due to the aqueous solution, 

 while if the ratio was high, wetting was due to a paraffin film. It was 

 clearly necessary to avoid this wetting by paraffin as to it, moderate 

 scorching, when it occurred, was probably due. 



In order to test the properties of paraffin emulsions of different 

 formulae with regard to stabihty and wetting power a series of experi- 

 ments was started in the laboratory. The percentages of paraffin 

 tried were, 0, 1, 2, 5, 10, 15, 20 and 25 and the percentages of soap h, 

 1, 1| and 2. Mixtures were made with both distilled and tap water. 

 Each emulsion contained 100 c.c. of water and was made by syring- 

 ing the mixture of soap and paraffin, without the use of heat, several 

 times through the "rose" of a garden syringe. 

 Two points were then investigated : 



(a) The wetting power of the mixture, 

 (6) Its stability. 



Wetting Poiver. As these experiments were done during the winter 

 it was necessary to select some surface other than insects or fungi on 

 which to test the wetting. The glossy American cloth cover of an 

 exercise book proved a fairly good substitute. When the surface was 

 worn by the action of the liquids used it was renewed by applying a 

 thin film of boiled linseed oil which, when dry, gave a new brilliant 

 surface. 



Wetting took place either by means of the aqueous solution or by 

 the paraffin or by a combination of both. A drop or two of the Hquid 

 to be tested was placed on the American cloth surface and gently made 

 to roll. If the drop immediately spread and would form a thin stable 

 aqueous film it was given 3 marks for aqueous wetting. If it spread 

 but would not form an absolutely stable thin film it was given 2 marks, 

 while if it wetted shghtly only it was given 1 mark. If the drop 

 failed to spread much and left the faintest film of paraffin behind it on 



10—2 



