EXPERIMENTAL KNOWLEDGE OF THE PROPERTIES OF MATTER. 465 



Second Report on our Experimental Knowledge of the Properties 

 of Matter with respect to Volume, Pressure, Temperature, and 

 Specific Heat. By P. T. Main, M.A. 



Since tlie first part of tliis report was written further investigations liave 

 been made on some elements and compounds with the view of deter- 

 mining the variations in vapour-densitj with rise of temperature, and 

 the molecular weights of bodies. 



Vapour-densifi/ Determinations. 



In a paper contributed to the Royal Society of Edinburgh, July 18, 

 1887, Dr. A. Scott, using a modified form of V. Meyer's apparatus, 

 described in a paper published in 1879,^ obtains the vapour-densities, at 

 high temperatures, of a number of elements and compounds, and deduces 

 the molecular weights given below : — 



Na, K, Hg, S2, Csl, CsCl, Rbl, RbCl, KI, AgCI, PbOIs, MnCl^, FeCU, 

 CrCla, CdBrj. 



A table is given showing the theoretical numbers side by side with the 

 experimental. 



Vapour- densities of Nitric Oxide ; and of Antimony. 



In 1886^ Mensching and V. Meyer found that zinc had, at very high 

 temperatures, vapour-densities, such that Zn is the molecule of zinc, so that 

 mercury, cadmium, and zinc all consist of mouatomic molecules in the 

 gaseous state ; magnesium they did not succeed in volatilising ; but with 

 germanium, the boiling point of which is not far from that of zinc 

 according to Winkler, they hope to be more successful. 



In 1887 ^ they found that at a low temperature, viz., at 100°, nitric 

 oxide has the same vapour- density (relative) as at higher temperatures, 

 the contraction of the air in an air-thermometer and of the gas in a thermo- 

 meter filled with nitric oxide instead of air being precisely the same, as the 

 air and the gas were cooled equally. 



In ' Chem. Soc. Trans.' 1887, p. 397, Dr. A. Richardson shows that, 

 ■whereas the dissociation of nitric peroxide into NO2 molecules is com- 

 plete at 140°, a further dissociation of the NO2 begins immediately at 

 higher temperatures, and is completed at 620°, the pi-oducts being nitric 

 oxide and oxygen ; the density at 620° being two-thirds that at 140°. 



Mensching and V. Meyer,'* having found that at a white heat 

 the vapour- densities approached those corresponding to the molecular 

 weights P2, As2 for the elements phosphorus and arsenic, without, 

 however, quite reaching the values required, found at the highest tempe- 

 ratures vapour-densities for antimony which were less than for the 

 formula Sbg ; but, as they did not arrive at any temperature at which 

 the coefficient of expansion and the vapour- density remain constant, 

 they were unable to decide whether Sb2 or Sb is the molecular weight 

 of antimony. 



' Proc. Roy. Soc. London, 32, 1879. - Ber. 19, p. 3295. 



' Ber. 20, p. 1832. " JMd. 20, 1887, p. 1833. 



1888. ~ . H H 



