On the Direct Correlation of Mechanical and Chemical Forces. 149 



1 metre. Since it involves no arbitrary unit but the metre, I shall 

 adopt the last expression as the measure of the total amount of 

 mechanical work done by the solution of salts which expand in dis- 

 solving, and which may conversely be looked upon as the measure 

 of the mechanical force rendered latent and, as it were, expended 

 in the act of crystallization when crystals are deposited. The value 

 of this mechanical equivalent of course varies with the strength of the 

 solution, as already remarked. 



In the case of salts which occupy less space when dissolved than 

 when solid, pressure, like an increase in temperature, causes them to be 

 more soluble ; mechanical force is lost when they dissolve, and is, as 

 it were, expended in giving rise to solution. When water thus con- 

 taining more of a salt than could otherwise be dissolved at the same 

 temperature is just saturated under any given pressure, the amount of 

 pressure represents the force of crystalline polarity tending to cause 

 the salt to be deposited in a crystalline form, but which is exactly 

 counterbalanced by that pressure. I will not give the details for each 

 salt, but subjoin a Table of the results at which I have arrived for such 

 as illustrate particular points of interest, the calculations being all made 

 in accordance with the principles already described. I also give them 

 in the case of water, calculated from Thomson's experiments, assu- 

 ming that, when ice melts and mixes with water, it may be looked 

 upon as dissolving in it ; and, as will be seen, the mechanical force 

 thus deduced is of the same general order of magnitude as that gene- 

 rated by the crystallization of salts. 



I. II. III. IV. V. 



1. Chloride of Sodium 13-57 97 '407 '419 157 



2. Sulphate of Copper 4*83 60 1*910 3-183 7 



3. Ferridcyanide of Potas- 



sium 2-51 86 -288 '335 42 



4. Sulphate of Potash.... 31-21 63 1-840 2*914 42 



5. Ferrocyanide of Potas- 



sium 8-90 66 1-640 2-4S5 20 



6. Water 8-93 .. .. *991 106 



Nos. 2 and 5 are calculated as hydrated crystals. 



Column I. gives the expansion of each salt in crystallizing from a 

 nearly saturated solution in water, the volume in a crystalline state 

 being taken at 100. 



Column II. gives the actual pressure in atmospheres in the ex- 

 periment. 



Column III. gives the increased solubility due to the pressure 

 given in column II., the total amount of salt dissolved without pres- 

 sure being taken at 100. 



Column IV. gives the increase in solubility that would be produced 

 by a pressure of 100 atmospheres, as calculated in accordance with 

 the principles already described, the same unit being taken as in 

 column III. 



Column V. gives the value of the mechanical work that could be 

 done, or, so to speak, the amount of mechanical force set free when 



