416 Scientific Intelligence. 



nected first to a T tube, and by means of this to a vertical man- 

 ometer tube V3cm. long and 4 or 5mm. iu diameter standing in 

 mercury. The vertical portion of the T tube is attached, by a 

 rubber tube furnished with a pinch-cock, to the evolution tube. 

 This tube is about 12mm. wide for a distance of 5 or 6cm. at its 

 lower end, and is drawn out at the upper to enter the rubber tube. 

 Its lower end is closed by a rubber cork. The neck of the flask 

 is closed above by a rubber tube and a pinch cock, this tube being 

 large enough to contain the glass tube in which the substance to be 

 examined is placed. In making an experiment, the beaker, stand- 

 ing on a metal plate and surrounded with the upper half of a 

 somewhat larger beaker serving to prevent cooling by the exter- 

 nal air, is heated until the vapor of the heating material — 

 diphenylamine j for example — fills about two-thirds of its volume. 

 By exhausting the air through the rubber tube attached to the 

 vertical part of the T, the mercury is raised to a considerable 

 height in the manometer tube, the pinch-cock being then closed. 

 If the apparatus is tight, this height will remain constant. The 

 evolution tube, in which has been placed the sodium carbonate 

 contained in a small weighing tube, and also the sulphuric acid 

 necessary to decompose it, is then attached to this rubber tube, 

 the pinch-cock is opened and the height of the mercury in the 

 manometer tube is marked by means of a rubber ring. By inclin- 

 ing the evolution tube the acid comes in contact with the car- 

 bonate and evolves carbon dioxide, which depresses the mercury 

 column to a point marked with a second ring. The pinch-cock 

 above the flask is now opened and the substance allowed to fall 

 into the latter. Its vapor produces a still further depression of 

 the mercury, its level being marked with a third ring. Calling 

 the position of the first ring & 6 , that of the second Je b , and that of 

 the third k t , and taking the specific gravity of carbon dioxide to 

 be 1'529, the expression for the vapor-density D becomes 



D= - X 3-682 X- 



'K-K 



in which s and s' represent the mass of the substance and of the 



carbon dioxide respectively, and -jf — j 5 tne pressure-ratio of the 



carbon dioxide to the vapor. If s be made equal to s' so that the 

 mass of the sodium carbonate employed is equal to that of the 



substance, then the simpler expression D = 3"682Xt^ — y- 5 may be 



used, it being necessary only to determine the pressure-ratio of 

 the vapor to that of the carbon dioxide evolved from the same 

 weight of sodium carbonate. Vapor-densities of benzoic acid, 

 napthalene, phenol, aniline, nitrobenzene and benzene determined 

 in this way are given which are quite satisfactory. — Ber. JBerl. 

 Chem. Ges., xxiii, 919, Apr., 1890; J. Chan. Soc, lviii, 681, July, 

 1890. G. F. B. 



