1322.] Deposition of Crystals by Agitation. 171 



I threw the whole of the hquid and crystals upon a cotton 

 cloth. i\fter the liquid had passed through, the cloth contain- 

 ing the crystals was subjected to pressure between folds of filter- 

 ing paper as long as it imparted moisture to the paper. The 

 cloth with the crystals was then exposed to a gentle heat, 

 which was gradually augmented till all the water of crystalliza- 

 tion was driven off. The anhydrous salt obtained in this 



manner weighed 123-15 grains, or — — part of the salt. Now the 



water of crystallization belonging to 123*15 grains of anhydrous 

 carbonate of soda is 223*6 grains. 



As the crystals were deposited, the temperature of the mixture 

 was augmented by 14°, as accurately as I could determine. 

 The weight of the glass phial in which the solution was kept was 

 1351*7 grains. But the specific heat of glass is as nearly as 

 possible one-fifth of that of water. Instead of the glass, there- 

 fore, we may substitute a quantity of water equal to one-fifth of 

 the weight of the glass, or 270*3 gr. The specific heat of a 

 saturated solution of carbonate of soda is very nearly 0*75. We 

 may, therefore, substitute for the solution a quantity of water 

 weighing just three-fourths of our liquid, or 1879*2 grains. This, 

 with the water representing the glass, makes a total of 2149*5 

 grains. Now the water of crystallization of the crystals which 



were deposited (223*6 grains) constitute -^ part of the whole. 



Now if we suppose that this water during the crystallization 

 of the salt parted with the whole of its latent heat amounting to 

 140°, and that this was the cause of the augmentation of tem- 

 perature observed ; it is obvious that the temperature of the 



liquid would have been elevated ^7— = 14*46°. 



Though this is almost half a degree higher than the elevation 

 of temperature which I observed, I have no doubt that the 

 latent heat of the water of crystallization of the salt deposited 

 was the sole source of the heat observed. For my experiment 

 was exposed to two sources of error, which I could not com- 

 pletely obviate, and both of which had a tendency to make the 

 latent heat of the water of crystallization appear higher than the 

 augmentation of temperature observed. 



1. The salt took nearly three minutes before it was all depo- 

 sited, and during all that time, the temperature of the hquid was 

 augmenting. But as it was about 14° higher than the surround- 

 ing atmosphere, it is obvious that a portion of the heat must 

 have been dissipated before it reached its maximum; conse- 

 quently the augmentation of temperature which I observed must 

 have been a little less than the truth. 



2. The crystals of carbonate of soda which I collected on the 

 cotton cloth were exceedingly small, and they contained a great 



