146 Accessory Wetting Substances : Paraffin Emulsions 



24° hardness 2| % soap will be required for a 10 % paraffin emulsion 

 while for only 6° hardness only 1^ % will be required. 



Stability of Emulsions. In considering stability of paraffin emulsions 

 it must be pointed out that none can be kept indefinitely without 

 de-emulsification setting in. For practical purposes it is sufficient to 

 study their behaviour after comparatively short periods of time follow- 

 ing their manufacture. If they will remain stable for one hour it is 

 sufficient for practical purposes and experience shows that if any decided 

 de-emulsification is going to set in it does so in the first hour. In the 

 laboratory^ therefore, after the various emulsions had been tested for 

 wetting power they were poured, after thorough agitation, into burettes 

 and allowed to stand for one hour. 



It was found that all those formulae containing only | % of soap 

 in tap water were unstable and therefore dangerous to use. This agrees 

 with what might be expected from the plotted results of wetting power, 

 where the line indicating wetting by paraffin is always equal to or above 

 the line indicating wetting by aqueous solution. Similar emulsions 

 made with distilled water were stable even in cases (paraffin 10 % — 

 25 %) where, in the plotted results, the paraffin wetting hue is above 

 the water wetting line. These emulsions therefore, though not certain 

 to scorch, cannot necessarily be classed as safe. With 1 % soap and 

 tap water the emulsions were still slightly unstable, as might be 

 expected from the plotted results where the paraffin wetting hue is 

 nearly always above the water wetting line. These emulsions are 

 therefore dangerous except in those cases where the paraffin content 

 is low. Most plants will stand a very small quantity of free paraffin 

 if well distributed, since, under conditions of spraying, much of it 

 is evaporated before it can produce scorching effects. When however 

 much is present scorching is bound to occur. The other emulsions 

 tried, namely 1, 1|- and 2 % with distilled water and 1| and 2 % with 

 tap water, gave stable emulsions. It will be seen that in the case of 

 1| % soap and tap water at 20 and 25 % the paraffin wetting Une was 

 above the water wetting line, indicating that the emulsion was unstable. 

 Actually however when tested for an hour in a burette no appreciable 

 de-emulsified paraffin appeared. This should not be taken to indicate 

 that it is a safe emulsion to use. It contains a high content of paraffin 

 which is only just held in emulsion by the soap. In other words the soap 

 pellicule that separates the paraffin globules is nearly as thin as it can 

 be without actually parting asunder. So long as the hquid is at rest 

 it is stable, but when forcibly beaten against a solid object as in spraying. 



