TOOLS AND INSTRUMENTS. 



187 



as the water is forced in from the barrel through 

 the valve below. But the water itself is equally 

 pressed upon by the elasticity of the compressed 

 air, which acts like a spring till it regains its 

 natural space; and so long as this is not attained, 

 the water will be constantly forced up into the 

 tube, and be discharged in a continuous stream, 



or streams, according as it is allowed to escape 

 at top through a single pipe, or through the 

 perforations of a rose. We have thought it 

 necessary to endeavour to explain the principle 

 of these pneumatic engines, and it may be well 

 to give some idea of the force which may be 

 exerted by means of the above arrangement; 



Fig. 227. 

 Green's Garden Engine. 



Fig. 228.— 36-Gallon Water-barrow. 



for, in ignorance of this, certain parts are often 

 torn to pieces. By means of the leverage 

 afforded by the handle, a man pressing upon 

 the latter with a weight equal to 10 lbs., may 

 communicate to the piston a pressure of 100 

 lbs. on the inch, and this pressure will be com- 

 municated to every square inch of the interior 

 of the pipe, should any obstruction prevent the 

 discharge of the water. On a portion of a pipe 

 1 inch in diameter and 12 inches in length, the 

 pressure would therefore amount to 3770 lbs. 

 This shows that the machinist should make the 

 tubes very strong, and that the person who 

 uses the engine should not urge the piston too 



much, when he has cause to suspect that some 

 obstruction has taken place. One of the handiest 

 of these engines is Green's Garden Engine 

 (fig. 227). 



Improved Water-barrow (fig. 228). — This is an 

 excellent form of water-barrow, by means of 

 which several barrels can be in use at once, as 

 each barrel can be set down. The stout iron pivot 

 securely fixed to the sides of the barrel, drops 

 into a slot formed on the ends of the iron frame. 



Another useful form of water-barrow (fig. 

 229) is made with wrought-iron frame and gal- 

 vanized steel cistern. It is largely used by 

 Orchid-growers for dipping baskets, &c. 



