MISCELLANEOUS 233 



These are placed in a boiler with a few gallons of water and 

 heated to boil^ig, cold water gradually added, and the boiling 

 kept up for about two hours, until there are about 30 gallons 

 and all is dissolved. Then dilute to 100 gallons with soft 

 water. Sometimes potash is substituted for soda, and tallow 

 for fish-oil, and occasionally petroleum is also added. If the 

 pottish and soda are equally pure, 56 parts of potash are equal 

 to 40 of soda. 



Paraffin or petroleum emulsion is also very effective. It 

 can be made with either soap solution or sour milk. For the 

 former 1^ lb. of soap are dissolved in 2^ gallons of hot water, 

 then 5 gallons of paraffin are added, and the whole violently 

 agitated by a spray pump until an emulsion is formed. 1 

 gallon of the emulsion is then diluted with from 9 to 12 gallons 

 of water. 



The effect of the soap is merely mechanical, and the petro- 

 leum is not in any sense dissolved, but merely broken up into 

 minute droplets and suspended in the water. 



1 gallon of sour milk to 2 gallons of paraffin may also 

 be emulsified, and afterwards diluted wath water before 

 spraying. 



Some of the substances described under (A) also act as contact 

 poisons, being probably absorbed by the insect through the 

 skin. This is often the case with arsenic dips, calcium sul- 

 phide, sulphur, (fee, when used for blood- or sap-sucking 

 insects. 



IV. Plant Poisons. — These are sometimes useful to kill 

 weeds. A large number of substances act as poisons to plants. 

 Among those which have been most largely used are the 

 following : 



Arsenic and Arsenite of Soda. — These have been described 

 under "Insecticides." About 1 lb. of arsenious oxide or IJ lb. 

 of arsenite of soda to 10 gallons of water is the strength often 

 used. If arsenious oxide be used it should be dissolved by 

 boiling with water and about 2 lb. of soda. It should be 



