778 Transactions of the American Institute. 



160° Fahrenheit, which is probably the point of absolute cold, up to 

 its melting point. At thirty-two degrees Fahrenheit it begins to melt, 

 and the heat which it absorbs while melting is called latent heat. It 

 is found that it takes 142 units of heat to change one pound of ice 

 into water. If we take a pound of water at 174° and a pound of ice 

 at 32°, and put them together, we have two pounds of water at 32° ; 

 the 142° having been absorbed in melting the ice, without raising its 

 temperature. The water has a molecular motion that does not exist 

 in the ice, and to produce that motion has taken up 142° of heat. 



The next change is to convert water into steam ; and in that pro- 

 cess, 962 units of heat become latent. A very useful application of 

 this fact may be made to ascertain whether the water primes in a 

 steam boiler. If the water does not prime, the steam will heat water 

 according to the theory. If we take five pounds of water at 32° and 

 blow steam into it until we have six pounds, it will be boiling hot ; 

 but if any water is mixed with the steam, it will not heat it so much. 



If we heat steam to a certain point, it will be decomposed, and a 

 certain amount of heat will become latent in its disassociation. Spec- 

 troscopic observations of the sun, show that all the substances we have 

 on the earth, exist there in a state of disassociation. St. Claire Deville 

 ascertained that when steam is heated to 5,600° Fahrenheit, it is 

 decomposed into its elements, hydrogen and ozygen ; and that in that 

 disassociation not less than 8,000 units of heat become latent. We 

 have, thererefore : 



Water = Ice at 32°+142 units of heat. 

 Steam = water at 2129 + 62 units of heat. 

 H + + H = Steam at 5,300° + 8,000 

 units of heat. 



Water is the only substance which has been investigated. There 

 is a fixed temperature for every compound substance at which it is 

 decomposed. There is an extreme degree of cold at which chemical 

 affinities do not act, and an extreme degree of heat at which they do 

 not act. Between that range chemical combinations take place, and 

 above it they are decomposed by heat. 



We have hydrogen and oygen uncombined, and cause them to com- 

 bine, the latent heat of disassociation is set free, just as the latent 

 heat of steam is set free when it is condensed into water. It was once 

 thought that some of the specific heat was set free in combustion, but 

 that has been shown not to be true. The specific heat of water, 

 where the combustion has taken place, is as great as that of any sub- 

 stance in nature. But if we accept the statement of St. Clair Deville 



