CONTACT INSECTICIDES 315 



but a large amount of water may be used for either the dormant 

 spray or the summer spray. Its effect in killing insects is greater 

 because of the greater amount of grease in the crude oil. 



The strength of the emulsion is often indicated by the per cent of 

 oil or kerosene present in the diluted material; for example a ten 

 per cent emulsion would be indicated when the stock solution 

 above described is mixed with twenty gallons of water. 



Miscible Oils. — Soluble oils, or miscible oils are prepared and 

 are on the market for ready use in making spray materials. A 

 number of companies prepare such oils from crude oils or distillates. 



The chief use of the miscible oils is in fighting the San Jose" scale 

 which is the worst of all sucking insects. For winter spraying 

 against this insect about one part of miscible oil is used with fifteen 

 parts of water. Usually directions come with each lot for making 

 up the spray for different purposes and at different seasons. It is 

 important to have the spraying done in dry weather and when 

 there is little danger of freezing too soon after spraying. 



Soaps. — Fish oil soaps have a disagreeable odor and are good repel- 

 lants. They are often sold under the name of whale oil soap, but 

 there is probably little on the market made from whale oil. Strong 

 soap of any kind when dissolved in water is good to use on tender 

 plants for destroying plant lice and other soft bodied sucking 

 insects. Very strong soap suds should be used. Cottonseed oil and 

 other cheap oils are used for making soaps to be used in spraying. 

 A good formula for the home preparation of such soap is caustic 

 soda, six pounds; fish oil or other oil, twenty-two pounds; water, 

 one-half gallon. First dissolve the caustic soda in the water then 

 add the oil gradually while stirring vigorously. If this work is 

 done in a warm place boiling will not be necessary. The longer 

 the stirring is kept up the better the soap will remain in suspension. 



Nicotine Sulfate. — This is an extract of tobacco containing about 

 forty per cent of pure nicotine sulfate. It can be combined with 

 other sprays as lime-sulfur, arsenate of lead and soap solutions. It 

 is well to always add some soap to the whole solution to help make 

 it spread better over the plants. 



A commercial form of this preparation is known as "black leaf 

 40. " This and the commercial nicotine sulfate are used in strengths 

 varying from one part in 800 parts of water to twice that dilution. 



Nicofume is a preparation of paper saturated with nicotine 

 sulfate. It is used chiefly for fumigating green houses. The satu- 

 rated paper is burned when dry. 



