464 



THE GUIDE TO NATURE 



gas acts on the piston as the powder on 



The force 



the bullet in a cartridge 



shut off or the sparking stopped by 

 throwing off the switch. 



Such an engine belongs to those of 

 the internal combustion type, in which 

 the fuel is burned in the cylinder in- 

 stead under a boiler. 



Fig. 1. — Two halves of flask, A and B, containing 

 the moulding sand, showing the forms of the pat- 

 terns, C-C, just removed. These two flask halves are 

 put together, leaving the form of the cylinder inside. 

 The molten metal is poured in through holes left tor 

 the purpose and allowed to cool. The flask is removed 

 and the sand knocked away, leaving the rough casting 

 as seen at D. 



would shoot the piston from the cylin- 

 der, as the bullet is shot from the cart- 

 ridge, if it were not fastened to the 

 crank shaft carrying the heavy bal- 

 ance wheel which is set to spinning. 

 Charges of gas are continually admitted 

 to the cylinder at the proper intervrds 

 and there exploded. This keeps the 

 wheel rapidly spinning until the gas is 



Fig. 3. — Lathe "turning off" the rough exterior of 

 piston and bringing it to exact size and form. 



In the factory the first process is to 

 cast the crude iron into the form of 

 cylinder, piston and other parts needed. 



For casting, a smoothly finished pat- 

 tern of wood is made, cut in two and 

 the halves firmly laid in a mixture of 

 sand in a box called a flask. This mix- 

 ture is carefully packed around the pat- 

 tern and smoothed out by delicate in- 

 struments made for that purpose. 

 Every fragment of loose sand is then 

 blown away by the aid of small bel- 

 lows. 



Fig. 2. — A is piston head; B, the piston rings which 

 by their springiness maintain gas-tight contact be- 

 tween piston and walls of cylinder. C is piston rod; 

 D, cylinder. These pieces are finished ready for put- 

 ting together. The rule is to show comparative size. 



Fig. 4. — Some of the parts of the engine: A. eccen- 

 tric and rod; B, make and break sparker; C, .'il cup; 

 D, crank shaft. 



