156 Principles of Plant Culture. 
resembling milk. Dilute to 22 gallons for use. This 
mixture may be used during the growing season; or 
b — Place 30 pounds of resin, 9 pounds of 70 per cent. 
caustic soda and 44 pints of fish oil, in a closed iron kettle 
and cover with five or six inches of water. Boil until the 
liquid has a dark-brown color, after which slowly add water 
until the whole makes 100 gallons; or dilute a part of the 
liquid at this rate, keeping the remainder as a stock solution. 
This is for use in the dormant season. For use in the 
growing season, similar solutions are used with more 
dilution. 
297. Hydrocyanic Gas. Another method of destroy- 
ing scale insects used in California and the Southern States 
is to treat the tree, which is first inclosed in an oiled-cloth 
tent, with hydrocyanic gas. One ounce of cyanid of pot- 
assium and one measured ounce of sulfuric acid are placed 
in an earthen or leaden jar containing three measured 
ounces of water. The jar is covered with burlaps to pre- 
vent the rapid escape of the gas. The tent is left over the 
tree fifteen minutes to one hour. It is advisable to apply 
this treatment during the dormant season, and in a cool 
period. 
998, Fir-Tree Oil, is considerably used for destroy- 
ing scale insects and the mealy bug* in greenhouses and 
conservatories. It is mixed with warm, soft water at the 
rate of a tablespoonful of oil to a pint, and applied with a 
syringe; or the plants are dipped into the mixture. 
299. Hot Water may also be used for destroying the 
above-named insects (298) and plant lice (aphid). Infested 
pot-plants are inverted and immersed five or six seconds 
* Dactylopius. 
