570 MACHINES, WORK, AND ENERGY 



the chief difficulty with Newcomen's engine was the loss of 

 heat energy about the cylinder. He was determined to re- 

 duce this loss; to do so he made three important improvements : 



First, Watt saw that the spray of cold water forced into the 

 cylinder at each stroke so cooled the cylinder and piston that 

 a large amount of the energy in the steam admitted at the 

 next stroke was consumed in reheating the cylinder. He 

 therefore provided for the condensation of the exhaust steam 

 in another vessel (H, Fig. 356) which was constantly sur- 

 rounded by cold water. He also surrounded the cylinder with 

 a jacket of steam. 



Second, Watt made his an all-steam-engine whereas New- 

 comen's was an air-steam engine. His purpose in doing so 

 was to keep the cylinder hot. The upper end of the cylinder 

 of Newcomen's engine was open to the air and air pressure 

 was used to force the piston down. The piston and cylinder 

 were, therefore, constantly losing heat to the air. Watt closed 

 both ends of the cylinder of his engine and made the piston 

 rod work through a STUFFING BOX, a small opening packed 

 steam-tight, just as steam engines are constructed today. 



Third, Watt's third improvement was to use oil to lubricate 

 the piston and prevent the steam from passing it. It was 

 impossible in those days for mechanics to make the pistons 

 and cylinders as true and close fitting as they are made 

 today. To prevent the steam from escaping past the piston 

 as well as to lubricate it, Newcomen kept a stream of water 

 running constantly upon the upper surface of the piston of 

 his engine (Fig. 354). This water absorbed a large amount 

 of the heat from the steam. 



These improvements by Watt greatly increased the effi- 

 ciency of the steam engine. It now did the same amount of 

 work while using but about one-fourth as much coal as New- 

 comen's engine used. We must remember that Watt's motto 

 was: "Keep the cylinder and piston as hot as possible all the 

 time," a rule which is followed in all steam-engine construction 

 today. 



