298 



Mr. J. B. Hannay. 



This leather face is then oiled, and can be screwed up with much less 

 damage to the india-rubber plug. The larger the screw the more 

 easily is it kept tight. The first screw I used was T 3 ¥ of an inch, and 

 it soon cut the leather facings ; the second was -j^, and it was found to 

 last much longer ; and now working with a half -inch screw it has not 

 required repacking for three months, although in constant use. The 

 dimensions of the apparatus as used are as follows : — Length of hori- 

 zontal tube, 24 inches ; height of vertical branches, 8 inches ; caps, 

 2 inches long by If inches diameter ; screw, -J inch ; external diameter 

 of tube, inches ; internal diameter, f inch ; length of manometers, 

 22 inches to 26 inches ; external diameter, \ inch to f inch ; internal 

 diameter, from inch up to inch. Small bath, 5 inches high by 

 4 inches diameter ; larger bath, 7 inches by 6 inches ; external cover, 

 13 inches high by 9 inches diameter. In each of the baths and in the 

 cover two vertical slits were cut and fitted with mica windows, and a 

 light placed behind allowed an observer to see clearly what occurred. 

 The measurements are given in English standards, as engineers who 

 construct such apparatus always use that method of measurement. 



As Amagat has shown that hydrogen is the only gas which follows 

 Boyle's law at high pressure, that gas was always used as the mano- 

 metric substance, and was carefully purified and dried before use. 

 The drying was done by passing it through five (J -tubes with pumice- 

 stone and strong sulphuric acid, and then through two (J -tubes with 

 phosphoric anhydride. The manometers used were always 0*4 millim. 

 in internal diameter, as narrower manometers always gave higher 

 readings. In determining the pressure of alcohol at its critical tem- 

 perature, the difference of pressure indicated by different manometers 

 puzzled me at first, especially as there was no difference in temperature, 

 but upon determining the diameters of the manometer tubes it was 

 found that the highest pressures were registered by the smallest 

 bores. 



The pressure of alcohol at its critical point as registered by the 

 different manometers was as follows : — 



Temperature (theory) . Diameter in Pressure in 



millims. atmospheres. 



232-14 0-142 69 7 



232-07 0-272 69 T 



232-12 AO -480 68 T 



231*99 B -628 67 -9 



These numbers are the means of thirty measurements in each case. 

 The manometers A and B were used in most of the first portion of the 

 work, but as they both broke subsequently, they were replaced by two 

 others, A' and B', and these again by A" and B". When a pressure of 



