Reaction before Complete Equilibrium, 275 



necessary, if even moderately dilute solutions should be investi- 

 gated. The present systems o£ reading the pressure up to 

 OOOl mm. seem to me also not to be reliable and accurate to 

 the same extent. 



Passing to the metlwds of solubility, we have to note in the 

 first instance that the value o£ G 7/ in the equation 



^=O'(t -t){t-t„ + K) 



is considerably smaller in case of separation of the salt from 

 a supersaturated solution, than in the case of separation of 

 ice from an aqueous solution. The first reactions last a few- 

 minutes, while the i second ones only last from 15 8 to 30 s . 

 The value of C' is accordingly (see tables in Part I.) about ten 

 times smaller for the first than for the last. In the different 

 methods in use about 100 c. cm. liquid and a liquid-bath are 

 usually employed, no account being taken of the proper 

 arrangement of the convergence-temperature. On the con- 

 trary, the value of T„ T O0 or the surface of the solid salt in 

 contact with the liquid is usually great, and can be taken 

 even considerably greater than in the case of the freezing- 

 point method. The principles to be followed here for the 

 development of the method are the same as in all other cases : 

 a greater quantity of the liquid in an air-bath, which is 

 placed in a liquid- or vapour-bath of a suitable consiant 

 temperature, should be used, and the convergence-temperature 

 should be kept very near the point of equilibrium. A great 

 value of T — T op should be provided for so as to compensate 

 for the small value of C". For this the solid should be 

 present in great quantity and finely divided in the liquid, &c. 

 The method can also be arranged in a way quite analogous 

 to that of freezing-point, and the experiments given above 

 show that the results in this case are very successful. Since 

 C" is not very great here, and all the conditions necessary for 

 securing a successful experiment have to the present not 

 been taken sufficiently into account, there is no wonder that 

 the results obtained by different investigators almost always 

 differ considerably from one another, and that almost all of 

 the results in this region of investigation cannot claim to be 

 of great accuracy. Especially at higher temperatures, where 

 the values of C(t q —t), or velocity of cooling by the surround- 

 ing medium, become very great, we find that the results 

 prove to be very much affected by experimental errors, as 

 could be easily illustrated on the run of a great number of 

 curves. 



