432 
JOURNAL OF ECONOMIC ENTOMOLOGY 
[Vol. 16 
If not enough soap, in addition to that broken down to fatty acids and 
alkali, to form the films for the droplets is present, the emulsion will not be 
permanent. There will be nothing to prevent the droplets from coales¬ 
cing and the oil will therefore separate out. There need not, however, 
be a large excess of soap. It is possible to utilize nearly all of the soap 
from a solution for the formation of film. 
Soap Remaining in Solution 
The excess soap remaining in solution in the water is of no value in so 
far as stabilizing the emulsion is concerned. In the application of sprays, 
however, their wetting and spreading qualities are of very great import¬ 
ance. Soapy water wets foliage and spreads on it much better than water 
without soap. This is connected with the lowering of surface tension 
caused by the addition of soap to water. The surface tension of water 
is very much lowered by the addition of small quantities of soap. 
Larger quantities do not affect it proportionately. There is probably, 
therefore, an optimum concentration of excess soap which may be used 
in the emulsion. This quantity must be determined by experiment. 
Experimental Emulsions 
To illustrate the partition of the soap in practice, a kerosene emulsion 
made by the method of Ouaintance and Siegler, 4 using commercial neu¬ 
tral sodium fish-oil soap, was analyzed. It contained 1.80% of dry 
soap. This was distributed in the emulsion as follows: 8% of the soap 
was lost by hydrolysis and solution in the kerosene; 12% was used in 
the formation of films to keep the droplets of oil from coalescing; and 
80% remained in the water solution. 
Another emulsion was made in the same manner, except that a small 
quantity of sodium hydroxide (about 30 cc. of noimal solution per liter) 
was added to the soap solution. In this case the droplets were slightly 
larger than in the first emulsion owing probably to variation in the 
agitation. None of the soap was hydrolyzed. About 9% was used in the 
formation of films, and the other 91% remained in the water solution. 
DELAYED EMERGENCE OF HESSIAN FLY FOR THE FALL 
OF 1922 
Bv W. B. Cartwright, 
Assistant Entomologist, U. S. Bureau of Entomology, West Lafayette, Indiana 
Abstract 
A delayed emergence of Hessian fly occurred within a triangular area bounded 
by the Mississippi and Ohio Rivers and a line drawn eastward from St. Louis. Ab- 
4 loc. cit. p. 28. 
