Sir G. Cayley on the Natural Zero. 89 



of different fluids, as those of asther, alcohol, &c. are found to 

 expand with equal uniformity by equal additions of tempera- 

 ture; but that each vapour has its own grade of elasticity: and 

 hence that privation of caloric at which elasticity would cease, 

 diffei's in eacli ; chemical affinity between the particles in these 

 cases seems to exert to a certain extent a controlling power 

 over caloric, and to modify its action. There is also a che- 

 mical combination of caloric with these fluid substances when 

 they change to a state of vapour, which may materially affect 

 their relation to transferable caloric: thus steam of 212° con- 

 tains about 960° degrees of caloric in chemical union, which 

 does not affect its temperature. It depends upon the degree 

 of pressure the water is exposed to, at what temperature it will 

 rise into vapour and commence this vast but imperceptible 

 absorption of caloric. An additional pressure of three pounds 

 per square inch, requiring about ten degi'ees more tempera-- 

 tare before vaporization commences ; hence the power, what- 

 ever it be, by which the caloric enters into chemical union at 

 202°, is three pounds per square inch less forcible than at 212°, 

 and six pounds less than at 222°, the whole power at 212° be- 

 ing equal to about fifteen pounds per square inch. The same 

 ratio exists as to this power in alcohol at 176°, and in aether at 

 about 98° ; in the former 38 degrees below the boiling point 

 of water, and in the latter 128°. The expansive power arising 

 from temperature in these cases is evidently modified by the 

 chemical affinities of these substances, as is rendered more evi- 

 dent by the circumstance that asther, the boiling point of which 

 is so much below that of alcohol, freezes at — 46°; whereas 

 alcohol has been exposed to a temperature of —91° without 

 freezing ; and it rests on one authority only that it can be con-: 

 gealed at all, and that at a temperature of —110°. The stri- 

 king circumstance with respect to the permanent gases is, that 

 they all agree as to the privation of temperature at which they 

 would cease to be elastic. In their chemical formation they seem 

 to have embodied permanently as much caloric as neutralizes 

 all attraction between their particles ; and hence every addi- 

 tion of temperature from the natural zero exhibits an expan- 

 sion, or a force equivalent, if unrestrained, to generate ex- 

 pansion. 



When we see that a few pounds pressure per square inch 

 has so much effect upon fluids when upon the point of rising 

 into vapour, and contemplate the power which the particles of 

 water exert when passing into the state of ice, so as even to 

 split bomb-shells and cannon, — it seems very probable that in 

 vapours, the effects of temperature are disturbed by counter- 

 acting forces, but that they have their full and undisturbed in- 



New Series. Vol. 5. No. 26. Feb. 1829. N fluency 



