4 



tobacco are often mixed with petroleum or other compomids to 

 enhance their insecticidal value. There are many proprietary 

 preparations of tobacco on the market, which are ready for use 

 directly when mixed with water, and save most of the trouble of 

 preparation. To make a tobacco decoction at home steep tobacco 

 (stems usually) in an amotmt of water sufficient to cover them 

 and when the active principle has all been extracted, strain and 

 dilute the liquid taken off with water until it has an amber color, 

 when it is ready for use. 



Sulpliur. Sulphur in the form of flowers of sulphur is val- 

 uable as an insecticide for thrips and red spider. It is used a 

 good deal in greenliotises, where it is evaporated in a sand bath 

 over an oil stove, or it may be applied directly to plants as a jdow- 

 der. Sometimes it is mixed with water at the rate of 1 oimee to 

 the gallon of water : or tlie plants may first be moistened and the 

 sulphur dusted on. 



Pyretlirum. Pyrethrum powder or buhach is conmionly used 

 here as a repellant for mosquitoes. The powder is obtained from 

 the flower heads of a composite plant, Pyretlirum cinerariaefo- 

 lium, and owes its value as an insecticide to the presence of an 

 oil which is poisonous to insects when they can be reached by it. 

 To free a room of mosquitoes, a small amount of the powder is 

 spread directly upon coals, or made into small pills by wetting 

 and moulding with the hands and then set on the coals. It is also 

 useful in destroying plant lice or thrips on small plants and may 

 be applied as a spray when dissolved in water at the rate of 

 1 ounce to 3 gallons or dusted onto plants after diluting' it witli 

 from six to twenty parts of flour. 



INSECTICIDAL GASES. 



Hydrocyanic acid gas and the fumes of carbon bisulphid have 

 now come into rather general use as insecticides, the former in 

 tlie treatment of fruit trees or smaller plants badly infested with 

 plant lice, mealy bugs, scale or other insects, and both in treating 

 infested foodstuffs, seeds, plant stocks, furniture or other mate- 

 rial which can be enclosed in an air-tight compartment and snb- 



