158 REPORT 4, UNITED STATES ENTOMOLOGICAL COMMISSION. 
a portion of its value as an insecticide, and emulsions containing less than 30 per cent, 
of the oil, although they do not at all, or only very slowly, rise to the surface when 
diluted with considerable quantities of water, are nevertheless too much weakened 
for effective use against Scale insects. 
" The killing power of a diluted emulsion depends less upon the amount of emnlsion 
used in the solution than upon the percentage of oil contained in the emulsion. To 
increase the efficiency of an application we should rather add to the percentage of oil 
in the emulsion than increase the gross amount of emulsion used in a single applica- 
tion, the amount of the diluent remaining in each case the same." 
The following emulsions were used in the orange insect investigation 
by Mr. Hubbard, and were published in the Annual Eeport of the De- 
partment of Agriculture for 1881 and 1882, p. 115: 
Kerosene, 1 pint; sour cow's milk, 2 fluid ounces, dashed with a ladle; 2 drachms 
of powdered chalk was first added to the milk, and 2 ounces water during the stirring. 
An imperfect emulsion not readily suspended in water. 
Kerosene, 1 quart; solution of condensed milk, 3 parts; water, 5 parts, 12 fluid 
ounces. 
Emulsion made by spraying through the Aquapult pump and back into the pail. 
Stable, and readily suspended in water. 
Kerosene, 1 quart ; condensed milk, 12 fluid ounces, diluted with water, 36 ounces ; 
emulsified with the Aquapult. 
Kerosene, 25.6 fluid ounces ; condensed milk, 4.8 fluid ounces ; water, 14.4 ounces ; 
emulsified with pump. 
Kerosene, 2 quarts; condensed milk, 12 fluid ounces (1 can), water, 20 ounces; with 
pump. 
Kerosene, 2 quarts, 4 fluid ounces; condensed milk, 12 fluid ounces; water, 24 
ounces ; with pump. 
The following kerosene and soap emulsion has more recently been 
recommended by Mr. Hubbard : 
Kerosene, 2 gallons. Common soap, £ pound ; water, 1 gallon. 
Heat the mixture of soap and water, and add it, boiling hot, to the kerosene. Churn 
the mixture by means of a force-pump and spray nozzle for five or ten minutes. The 
emulsion, if perfect, forms a cream, which thickens on cooling, and should adhere 
without oiliness to the surface of glass. Dilute, before using, 1 part of the emulsion 
with 9 parts of cold water. The above formula gives 3 gallons of emulsion, and 
makes, when diluted, 30 gallons of wash. 
With this important discovery a wide field for further experimentation 
with kerosene has been opened, while at the same time the perfected 
atomizing machines permit the kerosene water to be applied, even on a 
large scale and from below, in such fine spray as to greatly lessen the 
danger resulting from the influence of the kerosene on the plants. 
These improvements, in material as well as in appliances, being of recent 
date, we have had but little opportunity to try them in the field for the 
Cotton Worm. The experiments in 1880 of Mr. Schwarz, and upon 
which he gives the following report, were made with the imperfect emul- 
sion mentioned above: 
In my experiments with kerosene I uniformly used an emulsion of 1 part of kero- 
sene to 3 parts of milk. In view of the opinion expressed by Professor Comstock that 
such emulsion cannot be diluted with water, I would state that neither Professor 
Barnard nor myself experienced the slightest difficulty in this respect. This dis- 
crepancy is in all probability duo to the circumstance that our experiments were 
curr ied on on a small scale, where the difficulties in mixing the two ingredients are 
