Relations of Liquids and their Saturated Vapours. 91 



sity of vapour was found to be 0*23, which is exactly the value 

 computed from the line Of density. 



"Alcohol — Boiling-point 79'5 ; four tubes ; transition-point 

 281°. Five series of observations in good accordance. Density 

 of liquid 0*48, and of vapour 0*222. The same computed from 

 gradient is 0*245. 



cc Sulphide of Carbon. — Boiling-point 49°; five tubes; point 

 of transition 302°. The second, fourth, and fifth tubes give den- 

 sity of vapour 0'305, and of liquid 0*45. The vapour-density 

 computed from the gradient is (V305. 



"Chloroform. — Boiling-point 60°; three tubes; transition- 

 point 266°; density of liquid 0*42, of vapour 024. 



"Glacial Acetic Acid. — Three tubes ; no distinct point of trans- 

 ition. The liquid surface gradually fades away at about 315°, 

 but density of lower part greater than upper ; no activity mani- 

 fested in the tube ; density of liquid about 0*40 to 0'44, and of 

 vapour from 014 to 018. 



"Dichloride of Sulphur. — Four tubes ; transition temperature 

 estimated at about 500°, at which the liquid and the vapour are 

 of the same density, nearly 0*35 (the liquid unit density at 29°'5) . 



" Turpentine shows singular phenomena of change of colour 

 (becoming scarlet before transition) and decomposition. On 

 cooling, after transition, the liquid was thick and oily, deep 

 green by reflected light, and reddish brown by transmitted. On 

 opening the point of the tube there was a violent rush of gas 

 and effervescence of the liquid, which had first the odour of pitch, 

 then of creosote, and then naphtha, but had lost that of tur- 

 pentine. 



" It was remarked in these observations that near the transi- 

 tion-point the rate of apparent liquid-expansion becomes so very 

 great that it is difficult to keep the liquid surface steady ; it rises 

 and falls like a sensitive air-thermometer. The capillary attrac- 

 tion ceases, and from being concave the surface becomes first 

 quite flat, then convex like mercury." 



§ 30. The law of saturated vapour-density thus appears to be 

 strictly maintained from the zero of vapour up to the transition- 

 point. It is not altered by the liquid becoming solid (Begnault), 

 and is uninfluenced by the abnormal expansion of water. The 

 liquid molecules of water are abnormal in their change of volume, 

 while the vapour-molecules in contact with them behave as if 

 they were subject to the influences common to all the other 

 liquids expanding in the normal manner. 



Evidence as to the Law of Liquid expansion. 



dv 



dt, 

 § 31. This is given in Plate IV., where the values of — are 



