INSECTICIDES, PREVENTIVES, AND MACHINERY. 443 



few minutes, and we get first a milky appearance, which yields 

 rapidly to a cream, and this to a soft butter-like mass. When 

 cold, this will adhere to glass without oiliness, and the emulsion 

 thus made, containing sixty-six per cent, of kerosene, may be 

 readily mixed with water to any extent. It is also quite stable, 

 and will remain unchanged for a considerable time. It is worthy 

 of note that the emulsion is much more easily made with soft 

 water, and if the water is very hard a permanent emulsion is 

 difficult to procure. It is always advisable, therefore, to use 

 rain-water, or to soften the hard water by adding soda or borax. 

 Diluted from nine to twelve times, this emulsion is very effective 

 against plant-lice, against many scale insects, and against a great 

 number of others already referred to in previous chapters. Ex- 

 cept in its pure condition, or in an almost undiluted emulsion, 

 scale insects are not killed with certainty by kerosene, nor are 

 insect eggs often affected ; yet the material has an extremely wide 

 range, and is among the most useful of our contact insecticides. 



Another kerosene mixture is known as the " Cook emulsion," 

 made as follows : 



Soft. soap I quart. 



Water 2 quarts. 



Kerosene i pint. 



Dissolve the soap in boiHng water and add, boiling hot, to the 

 kerosene ; then churn as for the previous formula, and dilute 

 with an equal bulk of water before using. This is effective in 

 many cases as a mere soap-wash, and amounts to hardly more 

 than the addition of a little kerosene to strong soapsuds. The 

 formula is not recommended, except where the water is very 

 hard and no rain-water is available. 



A combination of kerosene and pyrethrum has been made as 

 follows : Percolate through one pound of pyrethrum one gallon 

 of kerosene, or in that proportion, and use the extract in place 

 of the pure kerosene : 



Hard soap i pound. 



Kerosene extract of pyrethrum i gallon. 



Water i gallon. 



Emulsify as before. 



