SPRAYING MACHINES. 



77 



contact poison. Stomach poisons are in general far cheaper ; contact 

 poisons for large insects require to be very strong and may injure 

 the plants ; stomach poisons should always be used if possible, but 

 if they cannot and no other method is available, we must use a contact 

 poison. 



In using insecticides we must have a method of putting them quickly 

 over a large surface of plant or insect. The value of insecticides lies 

 principally in the rapidity with which they can be applied to a large area 

 of crop. Insecticides can be applied in liquid form with water or as 

 powder mixed with lime, dust, flour, etc. An insecticide applied as powder 

 requires only to be dusted on from a bag and this is the simplest method 

 of application. A liquid insecticide must be applied as a fine spray or mist 

 that wets evenly and distributes the liquid properly over the whole plant. 

 For this work the spraying machine must be used. 



Spraying machines are of many kinds, all designed to fulfil the one 

 purpose of distributing fluid in a finely divided form over a large area of 

 plant. The simplest pattern is the tin hand sprayer (figs. 93-94). It 

 consists of a pump, which forces air out of a fine nozzle ; the compressed 

 air passes over the opening of a vertical tube, and sucks up a small quantity 



FIG. 94. 



Hand Sprayer ; details of construction. 



of the insecticide in the reservoir, throwing it out in an extremely 

 fine condition in the jet of air. The whole machine is made of tin and 



