390 Scientific Proceedings, Royal Dublin Society. 



of a similar nature. Thus it is possible that the specimen of hexamethylene 

 may have contained a very small quantity of trimethylpropyl methane, 

 although this impurity had been almost entirely removed by fractional 

 crystallization. Again, when ethyl alcohol contains a very little water, it 

 tends, on distillation, to separate into two components : — (a) a mixture 

 containing 4'43 per cent, of water,' and [b) pure ethyl alcohol. The first 

 component boils at a temperature less than 0-2° below the boiling-point of 

 the pure alcohol. 



6. When the liquid was distilled through a very efficient still-head, and 

 the distillate was collected in two or more fractions, these fractions showed 

 no difference in specific gravity. The presence of a trace of water in 

 ethyl alcohol can be conclusively demonstrated in this way, even when no 

 perceptible rise of boiling-point can be detected.^ 



7. In many cases more than one specimen of the liquid was prepared and 

 purified. Close agreement between (a) the boiling-points, (6) the specific 

 gravities, (c) the critical temperatures, ((/) the critical pressures, (e) other 

 physical constants of two different specimens of a substance may be taken as 

 a proof of the purity of both specimens. 



Apparatus and Methods of Determining the Physical Constants. 



Vapow-Pressiires. 



For the majority of substances three methods were employed, two 

 dynamical and one statical. 



1. From the lowest pressures to about 400 or 500 mm. the dynamical 

 method of Kamsay and Young' was found to be the most convenient and 

 to give the most accurate results. 



The apparatus (fig. 2) consists of a wide vertical glass tube. A, closed 

 below, to which a side-tube, £, is fused near the top. The side-tube is 

 connected with a bulb, C, which may be cooled by ice or a freezing mixture, 

 and from the bulb passes a second tube, D, which is connected with an 

 air-pump and gauge to reduce and measure the internal pressure. A small 

 tube, closed by an india-rubber tube and clip, E, serves to admit air into the 

 apparatus. The wide vertical tube is closed above by an india-rubber 

 stopper perforated with two holes, through one of which passes a thermo- 

 meter, F, and through the other a glass tube provided with a stopcock 

 and reservoir, G, above. The bulb of the thermometer is covered with 



' Fortey and Young, Trans. Chem. Soc, Ixxxi., p. 717, 1902. 



- Zoo. cit. 



^ Trans. Roy. Soc, clxxv., p. 37, 1884. 



