Speyers and Rosell — Resorcinol in Ethyl Alcohol. 449 



Art. XLIII. — Heat of Solution of Resorcinol in Ethyl Alco- 

 hol ; by C. L. Speyers and C. R. Rosell. 



When a system undergoes a change depending upon an 

 absorption of some particular energy, then as the intensity of 

 that particular energy is increased on the outside of the chang- 

 ing system, the amount of change inside the system is 

 increased ; when the system undergoes a change depending 

 upon a rejection of some particular energy, then as the intensity 

 of that particular energy is increased on the outside of the 

 changing system, the amount of change inside the system is 

 diminished. This statement is to be considered as universally 

 true though now and then a seeming exception comes up. 



The latest seeming exception that we have come across is 

 resorcinol with ethyl alcohol. Resorcinol dissolves in a large 

 excess of ethyl alcohol with rejection of heat* and yet the 

 solubility of resorcinol increases with the temperature. That 

 is, a change depending upon a rejection of heat energy seems 

 to be favored instead of being hindered, by increasing the 

 intensity of the heat energy on the outside of the system. 



But the mistake lies in joining a heat of solution in a 

 large excess of solvent, giving a very dilute solution, to a solu- 

 bility which implies a saturated solution and one more or less con- 

 centrated. The two solutions must be of equal concentration. 

 Wherefore the heat of solution in a nearly saturated solution is 

 the quantity that must be used, and its sign alone is enough, 

 its value is not needed, to test the validity of the above state- 

 ment. 



The sign can be found by diluting a saturated solution with 

 a small quantity of pure solvent. The method by supersatu- 

 ration fails for resorcinol, does not crystallize fast enough from 

 a saturated solution even to get the sign ; at least it did not do 

 so in the calorimeter we used. 



About 200 oc of saturated solution at about 27° were diluted 

 with about 10 co of pure solvent. The temperature rose more 

 than 0-2°. 



The act of solution may be separated into two parts ; namely, 

 one in which the solute liqueties, which always involves a gain 

 in energy to the system and is +, the other in which the lique- 

 fied solute mixes with the rest of the liquid to form the 

 desired solution. The second part may be + or — ; when it 

 is + then obviously the whole heat of solution must be +. 

 And this is the case for resorcinol, because concentrating a 



* Speyers, Journ. Am. Chem. Soc, xviii, 146, 1896. 



