Ijjlo.] On Iodines 209 



of a very liigh temperature ? * Supposing tTiese conjectures to 

 liave some foundation, it will remain to explain why, when we mix 

 equal volumes of water and of a solution of nitrate of ammonia at 

 the same temperature, the thermometer, as I have observed, sinks 

 more than 9°, though there is a notable increase of density. On 

 the supposition that the capacity of bodies for heat is a function of 

 the absolute quantity of heat which they contain, this fact would 

 lead us to admit that the capacity of the solution of nitrate of 

 ammonia is greater than that of its constituents ; but this conse- 

 quence does not appear to be confirmed by experience ; therefore 

 the capacity of bodies for heat does not depend solely upon the 

 absolute quantity of heat which they contain. 



I return now to the combinations of iodine with the combustibles, 

 or with those oxides which, not being saturated with oxygen, act 

 like combustibles. I have already spoken of the action of iodine oa 

 hydro-sulphuric and phosphorous acids. It remains only to speak 

 of its action on sulphurous acid. In the gaseous state this 

 acid has no action on iodine ; but when dissolved in water, the 

 addition of iodine occasions a decomposition of that liquid, and 

 sulphuric acid and hydriodic acid are produced. They cannot be 

 separated by distillation ; for at the temperature at which hydriodic 

 acid comes over, sulphurous is reproduced. The liquid in the 



• Chemical phenomena, in my opinion, cannot be explained by beat alone, 

 supposing Ilieni to depend solely on the variation of distance which it produces ia 

 the particles of these bodies. M. Laplace remarks (Systeine dii Monde, 3d edit, 

 ii. 256) that, in order to conciliate planetary attraction nilh chemical afCuity, 

 " we must suppose the dimensions of the particle:' so small, when compared witli 

 (.Se distances between them, that their density is incomparably greater than the 

 mean density of the whole together. A spherical particle, whose radius is equal 

 to the miUiont!i of a metre, ought to have a density more than six thousand 

 thousand millions greater than the mean density of the earth to produce at its sur- 

 face au attraction equal to gravitation ; but the attractive force of bodies consider- 

 ably surpasses that of gravitation, as they inflect visibly the rays of light, whose 

 direction is not sensibly changed by the attraction of the earth. Hence the density 

 of atoms would prodigiously surpass that of bodies, if their aSinities were only 

 nodifications of universal gravitation." 



Sucb a supposition appears exaggerated ; but let us admit it for a moment, and 

 fee whether the dimiuuliun of the affinity of a body corresponds with the increase 

 «f the distance of its particles produced by heat. Without knowing exactly the 

 cohesion of copper, for example, in a solid and liquid state, we may admit that it 

 It at least a thousand times greater in the foniuu' than in the latter state. Let us 

 luppose also, to keep greatly below the truth, that copper in melting increase* 

 eight limes in bulk. On this exaggerated supposition the distance between the 

 panicles of the copper would have only become double ; so that the cohesiou 

 klioulil have been only four ijincs siiialli'i if it followed the same law aa gravitu- 

 lion. Hence it ta obvious that,\4h(-M jit-iit unumululL's in a body, it does not diminish 

 the affinity merely by increasing the distance of the particles, but by incteasiiij; iu 

 u great degree the power of their repulsive farulty, which is doubtless the same 

 with Ihi'ir electric tucully. The figure, llie arrangement, and the inertia, of (ho 

 tiloms, inay have influence in nume chi-mical pli>'iioiiiena ; as, for example, in the 

 coneelalion of Wiiier, and the crystallisation of sulphate of ^uda. Hut there are 

 a-i iiilinily nf othris which are independeni of ihe^e, as well as of the separation 

 uf the aiouis. Such Is (be coiublnalion of hydrogen will) oxygen, which take« 

 {ilace only at a red heal, whclhcr the^usek be in a woodruicd or rapficd state. 



Vol. V. N*^ 111. O 



