﻿Chemistry and Physics. . 161 



" critical pressure," especially since the latter is already in use in 

 another sense to indicate the pressure at the critical temperature 

 of liquids. Whenever the fusing-point tension of a body is 

 greater than the atmospheric pressure, the substance is fusible 

 only by increasing the pressure upon it. This is the case with 

 arsenic, arsenous oxide, perchlorethane and carbon dioxide. The 

 vapor tension of C0 2 at its fusing point (—65°) is three atmos- 

 pheres. Hence solid carbon dioxide, under a less pressure, can- 

 not be melted but passes directly into the gaseous state. This 

 explains the fact that on issuing from the containing vessel, 

 liquid carbon dioxide becomes either solid or gaseous at once, 

 the pressure being below that at which the liquid can exist : i. e., 

 below the fusing-point tension. On the other hand, whenever 

 the fusing-point tension of a substance is less than the atmos- 

 pheric pressure, the phenomenon of non-fusibility can be pro- 

 duced only by reducing the pressure. At 0°, the tension of 

 water and ice is 4'6 mm . Hence below this pressure, ice is not 

 fusible. So for all substances the maximum pressure is deter- 

 mined by the fusing-point tension. According to Regnault, the 

 tension of benzene at 5° (its fusing point) is 35 # 6 mm . Hence 

 below this pressure, solid benzene cannot be melted even by the 

 most rapid heating. Experiment completely confirms this pre- 

 diction. On account of the less perfect vacuum required and 

 because of its less heat of fusion, this substance is admirably 

 suited to exhibit the phenomenon in question. A strong flask 

 having a lateral tube by which it is connected with a water 

 pump, contains a few cubic centimeters of benzene, in which is 

 placed a thermometer passing through the cork. The benzene 

 having been solidified in a freezing mixture, the flask is exhausted 

 below 35*6 mm of mercury and heat is applied. No fusion can be 

 observed. The experiment is facilitated by placing between the 

 flask and the pump a tubulated receiver cooled by ice, whereby 

 the benzene vapor is condensed and the vacuum is maintained. 

 On the question whether the temperature of the solid thus heated 

 ever rises above its melting point, the author calls attention to 

 the fact that with solids as with liquids, a definite vapor tension 

 corresponds to a fixed temperature, each temperature having its 

 own tension. Thus mercuric chloride, which has a fusing-point 

 tension of 420 mm , has at 200° a tension of 20 mm ; at 240°, 130 mm ; 

 at 265°, 250 mm ; and at 270°, 370 mm . So iodine, whose fusing- 

 point tension is 90 mm , has a tension of 20 mm at 85°, of 30 mm at 90°, 

 and of 75 mm at 110°. Since therefore the temperature controls 

 the tension, the fusing-point tension must be a fixed quantity and 

 the temperature invariable. Moreover at lower pressures, solids 

 can be heated only to temperatures corresponding to the given 

 tensions. — Ber. Berl. Chem. Ges., xix, 1057-1060, May, 1886. 



G. F. B. 



4. Studies from the laboratory of Physiological Chemistry, 

 Sheffield Scientific School of Yale College for the Year 1884-85. 

 Edited by Professor R. H. Chittenden. 198 pp. 8vo. New 



