Plants as Affected by Animal Parasites. 169 



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 



b Place 30 pounds of resin, 9 pounds of 70 per cent 

 caustic soda and 4y 2 pints of fish oil, in a closed iron 

 kettel 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 re- 

 mainder as a stock solution. This is for use in the dor- 

 mant season. For the growing season, similar, but more 

 dilute solutions are used. 



297. Hydrocyanic Gas. Another method of destroy- 

 ing scale insects is to treat the tree, previously inclosed 

 in an oil-cloth tent, with hydrocyanic gas. One ounce 

 of cyanid of potassium and one measured ounce of sul- 

 furic acid are placed in an earthen or leaden jar con- 

 taining three fluid ounces of water. The jar is covered 

 with burlaps to prevent 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. Nursery 



