78 THE SAX JOSE OR CHINESE SCALE. 
enough to wet the bark, and should not, to any extent, at least, run 
down the trunk. The collection of water and oil about the trunk is 
just as dangerous to the tree as is that of the pure oil. 
In the use of the oil sprays noted above one who has not had expe- 
rience with them is advised to make some careful preliminary tests to 
fully master the process, preferably waiting two or three weeks to 
determine the results before entering on the general treatment of the 
orchard. It is well, also, with the oil-water mixtures, to test the pump 
from time to time, spraying into a glass jar or bottle to determine by 
actual measurement whether the correct percentages of oil and water 
are being maintained. 
PETROLEUM-SOAP EMULSIONS. 
The kerosene-soap emulsion, following chiefly the Riley-Hubbard 
formula, has been one of the standard means against scale insects for 
twenty years. The distillate emulsion generalh" employed in Cali- 
fornia for spraying citrus trees, on which the lime, sulfur, and salt 
wash can not be used, is substantially the same thing, except that it 
is made with the California distillate or petroleum oil, Crude petro- 
leum of any kind, as well as the refined product, ma} T also be used in 
making this emulsion. The use of the soap emulsions against the San 
Jose scale in the East has not been very general, on account of the 
greater facility with which the pure oil or oil-water mixtures can be 
applied. The difficulty of obtaining uniform results with the latter 
has led to a return to the use of emulsions to some extent, and there 
can be no doubt about their superior merit when it is desired to dilute 
the pure oils. Emulsions may be applied at any strength with abso- 
lute confidence that there will be no variation. Where the emulsion 
can be prepared wholesale by steam power its employment is attended 
with no difficulties. In California it is prepared by oil companies and 
sold at very slightly more than the cost of the oil and soap ingredi- 
ents. It is made after the following formula: 
Petroleum gallons. . 2 
Whale-oil soap (or 1 quart soft soap) pound. . h 
Water (soft) gallon. . 1 
The soap, first finely divided, is dissolved in the water by boiling and 
immediately added boiling hot, away from the fire, to the oil. The 
whole mixture is then agitated violently while hot by being pumped 
back upon itself with a force pump and direct-discharge nozzle throw- 
ing a strong stream, preferably one-eighth inch in diameter. After 
from three to five minutes 1 pumping the emulsion should be perfect, 
and the mixture will haye increased from one-third to one-half in 
bulk and assumed the consistency of cream. Well made, the emulsion 
Avill keep indefinitely and should be diluted only as wanted for use. 
