Chap, xi.] the control of inse< i pests of crops. \\j 



crops 'it i tn 5 acres and for small orchards and gardens anil 

 tor larger areas under permanent crops, such as tea and coffee, in 

 districts which are impracticable tor larger machim ami 



of the unevenness of the ground. For the spraying of field crops 

 over large areas it is more economical to use Barrel Sprayei 

 Power Sprayers in all cases where the ground is sufficiently even to 

 enable such machines to rover it properly. 



Alter deciding on the size of machine required it is necessary to 

 seleet one of the various patterns obtainable on the market and in 

 doing this attention should be paid to their relative merits in order 

 ure the best value for money. It is impossible lure to adver- 

 tise or recommend particular makers or patterns, but information on 

 any points will alwaj to inquirers as far as possible. 



The material of the tank and of all working parts which come 

 into contact with the spray-liquid should be of heavy brass or bronze 

 or similar alloy. Many spray solutions (e.g. Bordeaux mixture) have 

 a corrosive action on iron, and copper is attacked by Lime-sulphur. 

 Xot only the tank, but the working parts of the pump itself (the 

 valves and theii seatings, the piston, and interior of the pump- 

 cylinder) must therefore be made of suitable material, as it does not 

 pay to buy cheap machines of inferior metals whicl 

 rapidly. 



fnciently large air-chamber should be insisted on, as its 

 presence has a considerable effect on the efficiency "I the spray. 

 If the chamber i- too small there will necessarily be considerable 

 variation in pressure between successive strokes of the pump, parti- 

 cularly in small machines, and the spraying will therefore tend to 

 be uneven. This item is of course eliminated in the case of 

 pressure sprayers. 



ssibility of the working parts of the pump is a matter to 

 which due attention should be given. In some of the older patterns 

 of machines the pump is enclosed in a tight case and i> practically 

 inaccessible without great waste of time. As grit and dirt are 

 to find their way into the pump and valves, these must occasionally 

 be removed and cleaned and therefore their accessibility is a 

 necessity. In this respect some of the pressure sprayers are very 

 satisfactory as the whole pump is easily removed for inspection. 



The packing of the piston must on noaccountbe made of rubber 

 but should be of some material which is readily replaceable, such 

 as leather. 



Strainers are important parts of all self-contained maehin 

 ssential to my that the spray-liquid is freed from all parti' 

 ' which will otherwise soon wear down the valves and clO| 

 nozzle. All spray-liquids therefore must be strained before they 



