452 Mr. Griffin on the Constitution of 



water, pass from the solid state to the liquid, and must ab- 

 sorb as much heat as is necessary to give them fluidity. The 

 thermometric heat is the difference between the heat produced 

 by condensation and the cold produced by change of state, 

 and in the present example the heat predominates. 



But when 179*91 septems of hydrated or crystallized car- 

 bonate of soda are dissolved in water, much cold is produced, 

 though not in consequence of the occurrence of the single 

 phenomenon of change of state from solidity to fluidity. It 

 is true, that the liquefaction of 179*91 septems of crystals, 

 and their dispersion through 23*29 atoms ( = 374*27 septems) 

 of additional water, producing a liquid compound of the bulk 

 of 540*54 septems, occasions the production of much cold, 

 yet it must be observed that the crystallized hydrate, in 

 forming this second hydrate, causes a condensation equal to 

 13*64 septems, which must unquestionably produce heat. But 

 since in this experiment the mass of matter to be liquefied is 

 almost five times greater than in the former example, while 

 the amount of condensation is one-third less, the single ther- 

 mometric result of the solution is a fall in temperature. Here 

 then we have evidently that "exception" which M. Gay- 

 Lussac was unable to find, that, namely, where " the heat 

 produced by hydration is less than the cold produced by 

 change of state." And this exception, so far from being a 

 rarity, must occur in every case where the atomic measure of 

 the substance to be liquefied is large, and its power of con- 

 densation but small. Without multiplying examples, I think 

 I may safely assume, that in all cases of solution the thermo- 

 metric heat or cold produced is not the effect of a single re- 

 action, but is the difference between the heat disengaged by 

 hydration and condensation, and the heat absorbed by lique- 

 faction or expansion. 



Upon this principle, it is easy to explain the heat produced 

 when strong sulphuric acid and potash-ley are diluted with 

 water, for as in these cases the substances are already liquid, 

 the effect caused by condensation is predominant. We can 

 also easily comprehend the cause of the great degree of cold 

 produced by dissolving sal-ammoniac in water. I shall show, 

 in a subsequent section, that 62*23 septems of anhydrous sal- 

 ammoniac, on being dissolved in 256*70 septems of water, 

 equal together to 318*93 septems, actually produce 326*80 

 septems of solution. Here the cold produced by the lique- 

 faction of 62*23 septems of the solid salt is added to the cold 

 produced by the expansion of 318*93 septems of solution to 

 326*80 septems, being an expansion of 7 '87 septems — equal 

 to one-eighth part of the bulk of thcsalt. And as in this 



