90 Sir G. Cayley on the Natural Zero. 



fluence with perfect uniformity in the gases ; and that all these 

 point to 480° below 32°, or 44'8° below 0°, as their tempera- 

 ture of non-elasticity or privation of all transferable caloric. 

 There is an apparent contradiction to this hypothesis in the cir- 

 cumstance that common air, when suddenly condensed seventy 

 or eighty times, kindles the tinder called amadou, and fires 

 gunpowder, &c. ; but as the capacity of bodies for caloric is in 

 some inverse ratio of their density, much heat must be evolved 

 by such a great increase of density ; even a red heat is soon 

 excited, by the condensation of soft iron under the hammer to 

 the extent of only l-33rd part of its bulk ; and hence the fact 

 is sufficiently accounted for, and is a case quite distinct from 

 the caloric of temperature. 



For the purpose of showing how small a proportion there 

 is between the ^^S degi-ees I have assumed as beyond the zero 

 of Fahrenheit, and the absolute quantity of caloric embodied 

 by some of the permanent gases, let two volumes of hydrogen 

 gas be condensed 448 times when of the temperature of 0° 

 Fahr. ; and as this is the proper proportion to generate water 

 by combustion, supposing the particles to be each of the den- 

 sity of water, they would not be reduced to contact by this de- 

 gree of condensation, but would have about sixteen times more 

 space unoccupied than occupied : hence their chemical consti- 

 tution would not be endangered unless done too suddenly, so 

 as to evolve caloric enough to ignite them. If this mixture 

 were I'educed to the temperature of 448° below 0°, the parti- 

 cles would then be in contact, and require no pressure to keep 

 them so. We may probably assume without much error, that 

 from the reduced capacity as to caloric, as much of it will have 

 escaped, from this cause, as would riiise the temperature of the 

 condensed mass about 900 or 1000 degrees, and at the same 

 time it will have lost by temperature 448° : thus it might be 

 said that 1448 degrees of heat are parted with by the gases 

 before they reach the natural zero ; but it is obvious that the 

 448° only are due to the account oi thermometrical temperature ; 

 the other to a separate and distinct cause; viz. the diminution 

 of capacity with respect to the caloric permanently embodied 

 in these gases by chemical combination, I shall quote from 

 some experiments by Count Rumford, on the caloric generated 

 by combustion, that one pound of hydrogen gas used as fuel 

 will raise 410 pounds of water from 32° to 212°, or 180° ; (this 

 estimate may not perhaps be very correct, but is sufficient for 

 my purpose) one pound of hydrogen gas requires eight pounds 

 of oxygen gas to saturate it in the formation of steam or water 

 by combustion ; and hence the whole caloric,which in the other 

 instance was applied to 410 pounds of water, is during the 



combustion 



