148 Journal of Agriculture, Victoria. [11 March, 1918. 



to shut off the spray when passing the interval between the vines in the 

 row. Interrupters are shown in Figs. 8, 9, 10, and 11. 



Pumps are of two types, viz., direct acting and air compressors. In 

 the former case the spray liquid is forced directly into the tube commu- 

 nicating with the nozzle, pressure being equalized by means of an air 

 chamber. Vermorel's well-known knapsack sprayer (Figs. 12 and 

 13) is based on this principle. In this machine the pump is much 

 simplified, the piston being replaced by a rubber diaphragm situated 

 at the base of the air chamber, and which can be raised or lowered by 

 operating the handle. Several sprayers on very similar lines to 

 Yermorel's are manufactured by British and American firms. 



In the second case, the reservoir of spraying liquid is so constructed 

 that it may be hermetically closed by means of a screw plug. The 

 pump, which consists of an air compressor, and not a pump for liquids, 

 compresses the air in the upper portion of the reservoir. An occa- 

 sional stroke of the pump maintains a sufficient pressure to insure a 

 satisfactory spray. 



In the case of a popular American sprayer worked by compressed 

 air, each outfit has its own air pump, which provides the necessary 

 compression after the reservoir has been charged with spray mixture. 

 As spraying proceeds, pressure necessarily falls. A few strokes of 

 the air pump soon restore it. An efficient interruptor and a strainer 

 to prevent clogging are useful features. 



By arranging the compressed air inlet at the bottom instead of the 

 top of the reservoir, the air bubbles rising through the liquid keep the 

 sediment in suspension and play the part of an agitator. 



In some types of sprayers the pump is detachable, the part carried 

 by the operator merely consisting of a reservoir, tube (Avith interrupter), 

 and nozzle ; the air pump is of similar pattern to those used for inflating 

 motor car tyres. The reservoir is half filled with liquid, and charged 

 with a sufficiency of compressed air to maintain the pressure until the 

 whole of the liquid is discharged, something after the style of a seltzogene 

 or soda-water syphon. Spraying outfits of this type have been devised 

 in which one central air pump serves for the charging of several knap- 

 sack sprayers. 



Limitations of the Knapsack Spray Pump. 



The knapsack spray pump, like other machines, has its drawbacks 

 as well as its advantages. True, it permits, in the hands of a careful 

 and conscientious operator, very thorough and economical application of 

 the spray mixture, more especially if provided with an interrupter. The 

 saving of copper sulphate thus rendered possible is worthy of serious 

 consideration, in view of the abnormally high price of this indispensable 

 salt at the present time. 



It also enables the spray to be ap])lied exactly Avhere it is roqnii'ed; 

 on the embryo bunches, for example, in the case of the first application, 

 in order to protect against the deadly bunch-mildew or grey-rot, Avhieh 

 was the main cause of loss of crop at Eutherglen this season. 



Another point which has given rise to considerable controversy is as to 

 whether the spray should be applied to the upper or under side of the 

 leaf. Infection by the fungus can only take place through the stomata 

 or breathing pores, which are situated almost exclusively on the under 

 side; this being so, it was contended by several authorities, some seA-en 



