1622.] Deposition of Cry St ah In/ Agitation, 173 



If we attempt to make a solution containing a greater propor* 

 lion of salt than that just stated, we shall find that it cannot be 

 cooled down without depositing crystals. The specific gravity 

 of the above solution at 87° is M995. I have never been able 

 to determine the specific gravity at 60°, but think it likely that 

 at that temperature it would be 1*228. 



When the above solution is cooled down to about 50° in a 

 well-corked phial, if we draw the cork, a copious deposition of 

 fibrous crystals make their appearance on the surface of the 

 liquid, and the crystallization in about half a minute extends 

 through the whole liquid, converting it into a semitransparent 

 fibrous white solid, while in the mean time the temperature of the 

 whole rises, as nearly as I have been able to determine, 24° of 

 Fahrenheit. 



One hundred grains of the residual liquid after the separation 

 of the crystals being evaporated to dryness left 8*62 grains of 

 anhydrous sulphate of soda. Hence it is obvious that this 

 liquid is a compound of 100 parts of water -f- 9*43 parts of 

 anhydrous sulphate. We see from this that very nearly two- 

 thirds of the whole salt in solution had been deposited in crys- 

 tals by an instantaneous crystaUization. 



In an experiment which I made, the weight of the glauber 

 salt solution was 2118 grains; and the weight of the phial in 

 which it was, amounted to 1032 grains. 



The whole sulphate of soda in the liquid, supposing it in a 

 crystallized state, was 1070 grains. Of this quantity, two- 

 thirds, or 713 grains, were deposited in fibrous crystals. Now 

 the water of crystaUization in this quantity of salt amounts to 

 very nearly 399 grains. 



The specific heat of a solution of glauber salt is about 0*73, 

 We may, therefore, consider the 2118 grains of the solution as- 

 equivalent to 1546 grains of water. If we reckon the specific 

 heat of the phial 0*2, we may consider it as equivalent to 206 

 grains of water, both of which together amount to 1752 grains. 

 Now 399 grains (the water of crystaUization of the salt) consti- 

 tute -—- of 1752 o-rains. Hence we obtain the amount of the 

 4-89 ^ 



heat evolved by the water of crystallization. If we multiply 24*^, 

 (the number of degrees of rise of temperature) by 4*39, the 

 product is 105-36°. 



It would appear from this, that the water of crystallization 

 does not, in the act of solidification, part with the whole of its 

 latent heat, but only with about three- fourths of it. But a phe- 

 nomenon which always has taken place in all my experiments 

 on this subject (and they have been numerous) enables us to 

 account for this apparent diminution of heat in a satisfactory 

 manner. When the phial containing the fibrous crystals mixed 

 with liquid is set aside for some days, the crystals subside, and 



