172 THE MONTHLY BULLETIN. 



SOAPS AND MISCIBLE OILS. 



By E. Ralph de Ong,* Eiitomologi-st, LTniversity of California Farm Scliool, 



Davis, California. 



The use of soap for insecticidal purposes received its first official 

 recognition in 1840. For many years soap was a popular remedy for 

 plant lice and has been used against the cottony-cushion and other 

 scale insects, especially in their immature stages. In 1885 extensive 

 experiments with soaps were besfun by Coquillett and continued the 

 following years by Albert Koebele, in an attempt to control the cottony- 

 cushion scale {Icerya jmrchasi), and the red scale (Aspidiotus 

 aurantii). which were then sweeping over southern California. In 

 the published report^ of this work we have a very complete record of 

 formula for insecticidal soaps of that time and but slight improvement 

 has been made since, for soon afterwards oil emulsions, together Avith 

 tobacco extracts, supplanted soap to a large extent as a spray in field 

 work; but for the garden and small orchard fish oil soap still holds a 

 place. To meet the demand for a soap that would be more readily 

 soluble in water than the ordinary soap of commerce, several liquid 

 soaps have been put on the market. These differ from the hard soap, 

 chiefly in the water content, this being from 50 to 70 per cent, while a 

 good hard fish oil soap will contain 20 to 30 per cent of water. Liquid 

 soaps when well made mix readily with water, making a very easily 

 prepared spray. 



Aside from the use of soap for its insecticidal value its chief use now 

 is in connection with other spray materials. Nearly all of our home- 

 made oil emulsions are based upon fish oil soap as the emulsifying 

 agent.- Tobacco extract, the second great rival of soap as an insecti- 

 cide, is more satisfactory when used with soap, as spray solutions made 

 from tobacco alone have a tendency to gather in drops on the leaves, 

 but spreads much better when used with soap at the rate of 4-8 pounds 

 to 200 gallons of spray, depending on the hardness of the water. 



WATER SOFTENING. 



When it is necessary to use hard water in making emulsions, and the 

 common methods of softening water have failed, the use of fish oil 

 soap at the rate of one to three pounds of soap to 50 gallons of water 

 in addition to the soap used for other purposes, has given good satis- 

 faction. The soap when dissolved unites with the lime, magnesia and 

 many other salts found in water, to form an insoluble soap, thus remov- 

 ing many elements that would have a tendency to break down the 

 emulsion. 



SOAP MATERIALS. 



The fish oil soap of commerce — or whale oil soap as it is frequently 



termed — is generally made of fish oil or "Menhaden oil," the latter 



being applied to a certain grade of fish oil obtained largely on the 



*I am indebtfd to Mr. George P. Gray, of the University of California, for chem- 

 ical advice in mv work on soap.s. 



'U. S. Dept. of Agriculture Report for ISSfi. 



=Mr. E. L. Morri.s, County Horticultural Commissioner of Santa Claia County, 

 recommends the use of rosin laundry soap as a cheaper emulsifier than wliale oil 

 soap. 



