P OLYTECHNIC ASSOCIATION. , 809 



it, the risk of losing it by wreck or blowing up, or by some chance 

 of business ; then we must allow for attendance and repairs ; then 

 there is the bulk of the fuel and machinery, and their weight, to be 

 taken into account. That, in a steamer, makes a tremendous draw- 

 back in the loss of freight and passengers. If you carry the principle 

 far enough, you will fill your steamer all up, and its whole business 

 will be paddling along. There have been some efforts to make six- 

 day ships for crossing the Atlantic, sacrificing everything to speed ; 

 but they put none of these traps into those ships, I assure you. 

 Although we may get economy of fuel, almost without limit, by 

 duplicating the apparatus in this way, it don't pay. 



Dr. Yan der Weyde — Another point. In heating water from 212° 

 to about 248°, you double the pressure, so that at least 2° are neces- 

 sary for every pound of additional pressure. But if you heat it to 

 500°, where the pressure is fifty atmospheres, then 15° will produce 

 fifteen atmospheres more pressure, or a whole atmosphere for every 

 degree. Here we have to keep the water at 500° and upward, but 

 there are other liquids that do not require that temperature. Take 

 the liquified carbonic acid gas, which boils at 148° below zero. Heat 

 it to 100° below zero and you have two atmospheres pressure ; an 

 additional atmosphere for about 48°. But heat it to 32° and you 

 have thirty-two atmospheres, and at 50° you have fifty atmospheres, 

 making a whole atmosphere for every degree. It is only necessary, 

 then, to maintain the ordinary atmospheric temperatures, and in the 

 summer all you have to do is to heat with the atmospheric tempera- 

 ture and to cool with ice'. Your engine will require no coal. But 

 you will have this drawback, that melting ice only consumes 140 units 

 of heat, whereas the combustion of coal gives out 14,000 units of heat. 

 For every pound of coal, therefore, you will want 100 pounds of ice ; 

 and ice is not so easy to keep, especially in summer, as coal. Another 

 difficulty is that the boiler must be strong enough to stand fifty to 

 sixty-five atmospheres of pressure. Of course this whole plan is 

 intensely absurd ; but as Cicero said that no theory was so absurd 

 that no man would adopt it, so in mechanics, no plan is so absurd that 

 no one will try to carry it out ; and there is a young gentleman now 

 endeavoring to carry out this plan. He will have a back pressure of 

 fifty atmospheres on his piston — a very respectable back pressure. 



Mr. Root — It seems to be the opinion both of Dr. Yan der Weyde 

 and of Mr. Stetson, that there is really a gain in using two liquids, 

 one boiling at a lower point than the other. To my mind that 

 is not so. I have drawn here two diagrams of cards taken from 



