PLANTS AND ANIMAL PARASITES 161 



to be applied to the dormant trees should have a specific 

 gravity of 1.03. 



296. Resin (or rosin) washes are valued for destroy- 

 ing various scale insects in southern and western United 

 States. They are adapted with modifications to both 

 dormant and growing trees. The resin is sometimes 

 saponified with caustic soda and simply diluted with 

 water; fish oil or petroleum may also be added. The 

 following and other formulas are in use : 



(a) Dissolve one pound of caustic soda in one gallon 

 of water in a covered iron kettle. Pour out half of the 

 solution, and to the remainder add 8 pounds of resin 

 and boil until dissolved. Then pour in very slowly the 

 rest of the caustic soda solution and boil the whole, 

 stirring it constantly, until it will unite with water, 

 forming a liquid resembling milk. Dilute to 22 gallons 

 for use. This mixture may be applied during the grow- 

 ing season ; or 



(6) Place 30 pounds of resin, 9 pounds of 70 per cent 

 caustic soda and 4| 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 the growing season, similar but more dilute solutions 

 are used. 



297. Hydrocyanic acid gas. Another method of de- 

 stroying scale insects is to treat the tree, previously in- 

 closed in an oil-cloth tent, with hydrocyanic acid gas. 

 One ounce of cyanid of potassium and one measured 

 ounce of sulfuric acid are placed in an earthen or leaden 

 jar containing three fluid ounces of water. The jar is 



M 



