.S7A' WILLIAM .s/A.I/A.Y.s, l-'.R.S. 337 



;;:; per cent., which, if the precaution he had mentioned \\i it- 

 taken, would he saved almost entirely. Again, in expanding the 

 compressed air, the difficulty of getting rid of the ice formed in 

 the passages of the expanding cylinder might be altogether sur- 

 mouuted if the water were injected into that cylinder at the 

 ordinary temperature, or better still at the temperature of 80 or 

 :ii' commonly existing in the bottom of a coal mine. This water 

 imparting its heat to the expanding air would prevent the forma- 

 tion of ice, and would produce precisely the same advantage as 

 that obtained in the compressing cylinder by the injection of water ; 

 and these two savings together would very materially alter the 

 result obtained in percentage of useful effect. The most perfect 

 arrangement indeed, if it could be carried out, would be to take 

 the very same water which had been injected into the com- 

 pressing cylinder, and inject it again into the expanding cylinder, 

 s<> that the heat taken from the air during its compression should 

 be restored to it during its expansion. By that means, if the 

 quantity of water injected were such as to keep the temperature 

 practically uniform throughout the stroke, the whole of the loss 

 at present arising from the heating and cooling of the air would 

 In- avoided, and there would be no loss of power beyond that due 

 to the friction of the machinery and pipes. The injection of warm 

 water into the expanding cylinder had not been made before, 

 he thought ; but with it air transmission might be accomplished 

 without greater loss of theoretical effect than water transmission. 



In the ilixcvKsion of the Paper 



"ON THE IRON ORES OF SWKIH-l.V." 

 By Mr. C. SMITH. 



Du. SIEMENS * said that he had listened (as he believed every- 

 body in the room had done) with very great interest to the paper 

 which had just been read ; there was, however, one point which 



* Excerpt Journal of tliclron and Steel Institute, Vol. I. 1874, pp. 320 and 823. 

 VOL. II. / 



