SIX WILLIAM SIEMENS, F.R.S. 137 



N it appeared likely that the sediment in the water would form 

 its'-lf into mud composed of an aggregation of separate small 

 particles ; and from the facts brought forward in the paper this 



d to be the action that really took place with the injection 

 of the heated air. With regard to priming, an interesting point 

 to ascertain in a boiler working with the air injection would be the 

 temperature of the water with reference to the working pressure of 

 the mixed steam and air : because when two gases co-existed in the 

 same space, each exerted its pressure independently of the other, 

 and therefore it seemed reasonable to infer that the temperature of 

 the water would be lower than the temperature corresponding to the 

 pressure in the boiler, in the proportion of the original pressure 

 of the steam alone to the actual pressure of the combined steam and 

 air in the boiler. Thus supposing that the steam in the boiler 

 were at a total pressure of three atmospheres, the water being at 

 the corresponding temperature of 275 Fahr., and that an equal 

 volume of air at atmospheric pressure were compressed and forced 

 into the boiler, the compressed air would expand again to atmo- 

 spheric pressure in the boiler during the transit of the air-bubbles 

 through the heated water, and each bubble of air would take up 

 steam by vaporisation until the point of saturation was reached. 

 The pressure of the mixed steam and air in the boiler would then 

 be four atmospheres, while the temperature of the water would 

 correspond to the density of the steam irrespective of the air 

 present, and would consequently remain that corresponding to a 

 pressure of only three atmospheres, the atmosphere of air permeating 

 the whole steam space in equilibrium, in accordance with the law 

 of the mutual diffusion of gases. It would be interesting to observe 

 whether this were really the fact ; and if it were so, he thought it 

 would explain the circumstance which had been mentioned in the 

 paper, that the moment the air was turned off violent ebullition 

 and priming took place. For as soon as the air was turned off, the 

 mixture of air and steam over the water in the boiler would no 

 longer be replenished by a similar mixture of gases ; and the 

 temperature of the water being below that corresponding to the 

 pressure of the mixed air and steam, a sudden collapse of the steam 

 would necessarily take place ; and as a consequence the engine 

 would require more steam, the throttle valve would open wide, and 

 the larger volume of steam suddenly called for would of itself 



