Insecticides and Related Substances. 305 



ever, because it decomposes more slowly and the sodium sulphite 

 formed is more subject to loss by washing than is calcium 

 sulphite. 



Kerosene has been used as a contact insecticide against scale 

 insects. It is applied as a spray to the dormant trees, but is 

 frequently injurious. Applied to stagnant pools, it effectually 

 suffocates the emerging pupae of mosquitoes; and in the "hop- 

 per-dozer" it destroys grasshoppers which are trapped in it, by 

 forming an oil film over the tracheae. 



Kerowater sprays were the result of attempts to dilute kero- 

 sene before applying it to trees. Kerosene is not miscible with 

 water but by forcibly mixing these liquids at the nozzle of the 

 spray pump the kerosene was temporarily diluted. 



Kerosene emulsions are comparatively permanent suspensions 

 made by mixing kerosene oil with soap solutions. They are not 

 true solutions, for the oil can be observed under a microscope as 

 droplets suspended in the soap solution. Well made emulsions 

 persist for several hours, and even for days, and facilitate an 

 even distribution of the kerosene. Crude petroleum oils, which 

 are closely related to kerosene but less volatile than the latter* 

 have taken its place to a great extent because of the greater 

 efficiency and safety attendant upon their use. 



Miscible oils are preparations of this nature. They are based 

 on a standard soap solution with which various proportions of 

 different oils are emulsified. Crude oil, a mixture of petroleum 

 oils heavier than kerosene; paraffin oil, a lubricating oil from 

 petroleum ; and resin oil, from the distillation of resin, are used. 

 The crude oils are efficient in 6 2/3 per cent strengths, whereas 

 kerosene is inefficient below 20 per cent strength. 



Penny gives the following formula for a standard miscible oil : 



The "Soap Solution." 



Menhaden oil 10 gallons 



Carbolic acid 8 " 



Caustic potash 15 " 



Heat to 290 or 300 F., then add kerosene 2 " 



Water 2 " 



