80 Preparation of Substances 



effective than the lime-sulfur as it creeps 

 under the bark reaching all places. One 

 thoro application of these oils will eliminate 

 scale from an orchard. 



When the miscible oil is not properly 

 made by the manufacturer in the first place 

 or when the apparatus used in dilution is not 

 clean some free oil may separate upon stand- 

 ing. If much of any oil appears the material 

 is worthless for spraying as the free oil kills 

 the twigs and small lims by penetrating the 

 bark. 



In the miscible oils the oil and the third 

 substance, a colloid in concentrated form, 

 have been put together and it only remains 

 to add water to make the emulsion. Their 

 condition is comparable to eg-yolk which 

 consists of 30 per cent fat diffused thru col- 

 loidal protein. 



Some idea of emulsions may be gaind from 

 the following remarks. 



It is possible to diffuse droplets of kerosene 

 thru water by violent agitation. Such sys- 

 tems are not stable as the droplets of kerosene 

 soon coalesce and separate. This is said to 

 be due to the great surface tension which is 

 a name for the tendency of small drops to get 

 together and get the most mass under the 

 least surface. Soap solution — a colloid — • 

 has a much less surface tension than kero- 



