PROCEEDINGS OF THE POLYTECHNIC ASSOCIATION. 485 



Mr. Rowell stated that he had been told by a gentleman that 

 there was a loss of eighteen per cent, by the radiation of steam. 

 He also stated that the limit of expansion should be controlled 

 by the power of the engine ; that the greatest loss was sustained 

 by the heating around the cylinder, and, that the screw-propeller 

 was denounced by many as a humbug, but that we would see the 

 day, which he believed was not far distant, when no other mode 

 of propelling would be adopted. 



The Chairman. — The question of how soon we will make iron 

 for Europe, instead of Europe sending her iron to us, gathers 

 around this question. The great prosperity of this country lies 

 in the development of the mineral and vegetable products of the 

 country. 



Mr. Dibben. — Mr. Isherwood did not pretend to say that expan- 

 sion was not economical. He said that the result of some experi- 

 ments made in the Brooklyn Water Works was, that there is a 

 saving of forty per cent, by the use of steam expansively. 



Mr. Montgomery, in alluding to an experiment made on the 

 "Wabash," stated that the result of it was so contradictory to 

 the principles of science that he should infer there must have 

 been something the matter with the steam apparatus. He went 

 on to explain the advantage of using steam at a high pressure. 

 He stated that the latent heat of steam under the pressure of one 

 atmosphere is nearly 1000 degrees, to which, if we add the 212 

 degrees sensible heat, we have a total of 1212 degrees. Under 

 a pressure of 10 atmospheres, or 150 lbs. to the inch, the sensi- 

 ble heat will have increased to 359 degrees ; but the total heat 

 will not be 1359 degrees, it will be as before 1212 degrees; the 

 latent heat becomes less as the sensible heat increases under high 

 pressure. The Cornish engine had become celebrated for its 

 value, simply because it introduced the "cut-off." 



The President enquired whether the Cornish engine was not 

 used in preference to others in all mines ? 



Mr. Montgomery. — I know of no others in use in mines. 



Mr. Rowell, in referring to the experiments at the Metropolitan 

 Mills, stated that they had kept one of the engines at full pres- 

 sure, with steam in the cylinder all day, and he found that al- 

 though clothed as effectually as possible, it required 18 per cent 

 of the heat that was required when it was running under the 

 same pressure. 



Mr. Montgomery. — There should not only be a steam-jacket 



