430 
JOURNAL OF ECONOMIC ENTOMOLOGY 
[Vol. 16 
insects were dislodged from these plants while a larger percentage of 
the insects fell from the dusted spireas. 
THE CONSTITUTION OF OIL EMULSIONS 
By E. L. Griffin, Associate Chemist, Insecticide & Fungicide Laboratory, 
Miscellaneous Division, Bureau of Chemistry, Washington, D. C. 
Abstract 
In an emulsion of mineral oil with soap and water the mineral oil is divided into 
very small droplets which are suspended in the watery medium. The soap is added 
to keep these droplets from coalescing and finally separating out. Its action is as 
follows: part of it is broken down, the fatty acids being dissolved in the kerosene 
and the alkali remaining in the water; part of it forms a film between the oil and 
the water, preventing the droplets from coalescing, thus stabilizing the emulsion; 
and any excess soap remains in water solution and helps the spreading qualities of 
the spray. 
The breaking down of the soap may be prevented, or at least made negligible, 
by the addition of excess alkali, thus preventing an apparent waste of soap. 
Two emulsions of the type used in practice were analyzed and the distribution 
of the soap in them reported. 
The oil emulsions used as insecticides consist of very small droplets 
of oil suspended in watery media. An emulsion can be formed of oil 
and water only, but it is unstable and the components soon separate. A 
stabilizer, usually a soluble soap, is added to overcome this tendency. In 
the past there has been little or no definite knowledge as to what happens 
to the soap in the emulsion and j ust what part it plays in the process of 
emulsification. There was, therefore, nothing to guide in the prepara¬ 
tion of an emulsion except previous experience as to what produced a 
satisfactory product. When difficulties occurred, and they were not 
infrequent, there was often no good explanation for them or guide to 
prevent them in the future. 
In a recent paper 1 the fate of the soap in the process of emulsification 
is shown to be as follows and in the order given. 
1. Part of the soap is broken dow T n (hydrolyzed) into the alkali and 
fatty acid from which it was originally formed and the fatty acid goes 
into solution in the oil, leaving the alkali in the w r ater. 
2. Part forms a layer or film of uniform thickness around the drop¬ 
lets of oil. 
3. All of the soap not used in 1 and 2 remains in the water solution. 
Hydrolyzed Soap 
Soaps in dilute water solution partially hydrolyze, or break down, into 
the alkalies and fatty acids from which they were originally made. The 
Griffin, J. Am. Chem. Soc., 45:1648 (1923). 
