PJRIMING GAUGE-COCKS. 



machine, and will be attended with the two-fold evil of injuring 

 the performance of the engine and wasting a quantity of heat 

 which would otherwise be employed in producing steam, and 

 therefore producing mechanical power. 



7. Nevertheless with all practicable precautions spray some- 

 times issues with the steam from the boiler to the engine. Steam, 

 in this condition, is like the air when a fine misty rain floats 

 in it, and is called WET STEAM by the engineers ; the steam 

 when free from this defect being called DRY STEAM. A handker- 

 chief held in dry steam issuing from the valve of a boiler will be 

 no more damped than it would be by a blast of wind ; but if the 

 steam be charged more or less with spray, its presence will be 

 shown at once by the moisture it would deposit. 



8. The spray with which wet steam is charged is called by the 

 engineers PRIMING. 



9. It appears, therefore, that whatever be the form of the 

 machine, or the purpose to which it is applied, it is of great 

 importance so to regulate the feed of the boiler, that the level of 

 the water in it shall neither fall too low nor rise too high. 



Considering then the great importance of keeping the level of 

 the water in the boiler within the limits here defined, it will be 

 evident that some expedient ought to be provided by means of 

 which the engineman can at all times ascertain what the level of 

 the water actually is. 



Different methods, all more or less efficient and ingenious, have 

 been invented for accomplishing this object. 



One of the most simple consists in two common cocks, called 

 gauge cocks, like those used in a beer barrel, which are inserted 

 in the side or end of the boiler, one of which is placed at the 

 lowest, and the other at the highest limit of the water level. If 

 the engineman, on opening the latter, finds that water issues 

 from it, he knows that the level has risen to its highest limit, and 

 he suspends the feed. If, on opening the former, he finds the 

 steam issue from it, he knows that the water level has fallen too 

 low, and he lays on the feed. But so long as water issues from 

 the one and steam from the other, he knows that the water level 

 is within the required limits. 



This method, though generally adopted, is not exclusively 

 depended on, and others are used. 



A weight F (fig. 2), half immersed in the water, is supported by 

 a wire, which, passing steam-tight through a small hole in the 

 top, is connected by a flexible string or chain, passing over a 

 wheel w, with a counterpoise A, just sufficient to balance F when 

 half immersed. If F be raised above the water, A being lighter 

 will no longer balance it, and F will descend pulling up A, and 



5 



