( 22(1 ) 



contamination of the Lydrogon has a great influence on the coriection, 

 this gas can only be applied when one disposes of a compression- 

 puinp as constructed at the Leiden laboratory (Proceedings, Dec. '94, 

 p. 168)^) by means of which the hydrogen can be re-com[)ressed without 

 its becoming impure. Compiessed air at GO atm. (about 120 m.m.) 

 gives a correction which can be applied with perfect certainty. 



In the case of lower pressures we can use commercial carbonic 

 acid from cylinders, if only one takes good care to dry it. At a 

 comparison at about 48,6 atm. we read on the manometer, after 

 having applied all the corrections except those fur the connecting 

 tubes between the separate manometers, a total column of mercury 

 of 36943,3 m.m. The correction for the carbonic acid columns was 

 but to — 144^8 mm. 



After the correction for the columns of compressed gas in the mano- 

 meter has been applied we must still take into account the column 

 of the gas between the level of the last meniscus of the manometer 

 and the level of the place at which we want to measure the prcssui'c 

 in the apparatus. The determination mentioned above referred to 

 the pressure in apparatus which were placed in a distant room ; 

 these were connected with the manometer by a conduit (40 M. 

 long) filled with carbonic acid; the difference of level amounted to 

 0,65 M. and the correction was -f 6,2 m.m. 



A second correction peculiar to this apparatus, must be applied 

 when the mercury in the manometertubes stands not perfectly still, as 

 even the slowest motion of it through the narrow tubes requires a 

 measurable pressure. If a velocity of 0.1 m.m. in a minute is ob- 

 served at the menisci in one of the separate manometers, this agrees 

 with an excess of pressure and with a correction of about 0.1 m.m. 

 For ihe streaming of the gas this correction would be uncertain as gas 

 may oveiflow without this being perceived at the movement of the 

 menisci. Theiefore the tubes along which the gas flows from the one 

 manometer to the other may not be too narrow. The diameter of the 

 steel capillaries is 0.6 m.m. They don't add to the friction more than 

 the glass capillaries and these are taken comparatively wide (comp. 

 § 2) so that when the apparatus is in a good condition we need 

 not pay attention to the motion of the gas. 



Usually thy filling of the tubes is done very slowly, the filling of 

 each tube takes about 4 — .5 minutes. Each time at the closing of the 

 stop-cocks the equilibrium is fairly well attained. If however a small 



') ('ominun. fr. the Plivsic-il J.Ml)or:itory at Leiden, 189J-. N". M pg. 7. 



