Polytechnic Association Proceedings. 853 



contents thirty times a minute into a small condenser, which will, 

 even then, maintain a veiy perfect vacuum. The amount of heat 

 conveyed by the steam from the ten or twelve large boilers, and 

 transferred to water in that little condenser, is almost incredible, 

 for if represented in mechanical force it would be equal, each 

 minute, to 840,000 horse-power. 



The reason why steam gives up its caloric with such amazing 

 rapidity is, that when the outside particles come into contact with 

 the condensing surface, they instantly condense and make room 

 for the next, and so on, until the last particle has rushed against 

 the sides, with as much speed as if there had been a vacuum between 

 them. 



I propose the following plan for a steam generator, viz: One 

 end of a large number of small tubes so arranged as to present a 

 large surface near to the fire, which, like the wire cloth, will rap- 

 idly absorb the heat. The opposite end of the tubes are inclosed 

 in the steam generator. These tubes contain a little water, the air 

 is expelled, and they are hermetically sealed so that the water in 

 them always remains there, and when cold, has a vacuum over it. 

 When this water, in the lower end of the tube, over the fire, is 

 converted into steam, the heat is instantly conveyed to the opposite 

 end inclosed in the generator, every inch of which will be kept at 

 the precise temperature of that which is over the fire. These tubes 

 are so near together in the generator, that only a thin stratum of 

 water surrounds them, and this is supplied at a high temperature, 

 by the feed-pipe, in the usual way. I presume most of you are 

 aware that the temperature at which these pipes will be maintained, 

 that of high pressure steam, is the one at which water is the most 

 rapidly converted into steam; if not, try the following experi- 

 ment. Heat an iron vessel red-hot and then carefully introduce 

 a little water. It will move around over the hot metal without 

 coming in contact, and evaporation will be very slow. Pour out 

 the water, and when the vessel has cooled down to 500° renew the 

 experipaent and nearly the same results will follow, only there will 

 be a little more evaporation, because the vapor upon which the 

 water rests is less rarefied. Now let it cool to 330°, pour in the 

 water and it will flash into steam in a few seconds. 



Three hundred and thirty degrees (varying a little for variation 

 of pressure), is the point at which water is by far the most rapidly 

 converted into steam; and that maximum point, varj^ing with the 

 pressure in the generator, is the precise temperature at which every 



