130 THE AMERICAN APPLE ORCHARD 



liquid by a suitable system of cocks, and the spray 

 mixture is blown out through the nozzles. When a 

 tube has been exhausted of its gas it is returned to 

 the soda water factory to be recharged. Counting 

 the cost of returning and recharging tubes, it may be 

 computed that this method of spraying, under favorable 

 conditions, costs about the same as to spread the same 

 amount of mixture by hand pumps. There are several 

 distinct advantages, however. The pressure is greater 

 and more uniform, so that much better work is the re- 

 sult. There is practically no machinery to break and 

 get out of order. The outfit is lighter to transport 

 about the farm than any kind of pump can be. The 

 better quality of the work is certainly the chief advan- 

 tage. 



These gas tubes give a comparatively high pres- 

 sure, ranging even above 200 pounds ; but this 

 pressure can be regulated accurately after a little 

 experience. A pressure of about 100 to 120 pounds 

 will be found best for ordinary work with bor- 

 deaux or lime-sulphur spray. 



