1821.] Causes of Calorific Capacity, Latent Heal, &;e. 449 



have w — W for the weight of the water not frozen. Since the 

 temperature after agitation rises to 1000, the aggregate temper- 

 ature after the agitation is 1000 {19 W - 22 (w - W)} = 1000 

 (22 w — 3 W). But the aggregate temperature before agita- 

 tion must have been 22 w t ; and because no temperature is 

 fained or lost by agitation, these two aggregates must be equal, 

 herefore 1000 (22 w - 3 W) = 22 w t, and W = 22 w x 



1000 - t 

 3000 ' 



Scholium. 



Dr. Thomson, p. 54, vol. i. of the sixth edition of his Chemistry, 

 says : " I find that when water is cooled down to 22° Fahr. very 

 nearly -^th of the whole freezes by agitation ; " " when the pre- 

 vious temperature is 27°, about -' T of the whole freezes." At 22° 

 Fahr. t = 989*5; therefore, putting w = 1, our formula gives 



w ' = 22 ^ = 3?ro = ts ver y nearf y> which differs from ir b y 



-pfgd part of the whole mass of the water. Again 27° Fahr. 

 gives t = 994-8 ; and, therefore, W' = 22 ~ = ilii = -i_ 



6 ' ' ...."...* 3000 30000 26-22 



very nearly, or r ± r , which exceeds -^ by ^j— or -^th of the 

 water operated on. Had Dr. Thomson, therefore, experimented 

 with a pint of water, or 20 oz. avoirdupois, which I expect is a 

 greater quantity than he employed, an error in the first instance 



of only — r oz. and in the second of — oz. in the determination 



of the quantity of water frozen would make his experiments 

 coincide with our theory. A less quantity of water experimented 

 with would give proportionably less differences. With experi- 

 ments of this kind there must be considerable difficulty in effec- 

 tually preventing the fluid part at the separation from taking 

 away with it some of the light, loose, incoherent solid which is 

 formed ; and hence it must usually follow that the theory will 

 give somewhat greater quantities than experiment, as we see it 

 happens in the present cases. 



If we could cool the water down so low that the whole of it 

 would congeal on agitation, we shall have W = w, and t = 1000 



*30OO 



— '-— ■ =863*6. Therefore could we cool water without freez- 



ESS 



ing to the true temperature 863-6, which corresponds with — 90° 

 Fahr. it would become one solid mass on agitation. Dr. Thom- 

 son calculates from his experiments that this would take place 

 at — 108°. It is curious that the number — 90° Fahr. coincides 

 with the greatest cold yet produced by mixing eight parts of 

 snow with ten parts of sulphuric acid diluted with half its weight 

 of water, the constituents being first at the temperature — 68° 

 Fahr. 



New Series, vol. li. 2 <; 



