OP ARTS AND SCIENCES. 



317 



The difficulty in obtaining such results is excessive ; for, apart from 

 the serious complications of the method itself, (thus it takes hours 

 before complete solidification sets in at the higher temperatures, and 

 minute stages must be observed in order to allow for radiation,) the 

 observer is dealing with au (under-cooled) substance, which at the mere 

 suggestion of careless handling begins to freeze prematurely, and 

 which in the liquid state tends to become impure by absorption of air 

 or water vapor. These decompositions are gradual, yet they cannot 

 be disregarded, because they lower the melting point and thus induce 

 early partial fusions and late complete solidifications. The table also 

 shows the difficulty in working at other than room temperature. 



7. Specific Heat. — For the reasons just stated, I shall have to give 

 my data for the specific heat of thymol provisionally ; for thougli I 

 made such experiments with great care and in considerable number, I 

 was not at tlie time fully conversant with the variety of precautions to 

 be taken to keep the substance pure. 



TABLK III. — Specific IIkat of Sor.in and of Liquid Thymol. 



These data, obtained with diflferent charges, arc much below the 

 sensitiveness of the method. The values for solid thymol, moreover, 

 show the unreasonably large influence of temperature, accounted for 

 in § 6. 



8. Molecular Pressure. — Taking the data of Table II. at their face 

 value, the only justifiable conclusion to be derived is that A is con- 

 stant for the interval 0" to 40°. AVithin the same interval the differ- 



