( 291 ) 



recently introduced by Hartman ') a difference of the levels of' the 

 mercury in the two cylinders is avoided, a difference which we 

 should have to take into account without being able to determine it 

 with sufficient certainty. The only thing now left to be taken into 

 account was the hydrostatical difference of pressure caused by a 

 different height of the mercury in the two tubes, and of the diffe- 

 rence in capillary depression caused by the difference in diameter 

 of the two tubes. An experiment made on purpose showed this 

 difference to be about 7 m.m., a quantity which could be neglected 

 as being smaller than the possible error of observation in the mea- 

 surement of the pressures. 



Suitable temperatures ranging between that of the room to a 

 little above the critical temperature of carbonic acid, were obtained 

 by means of an apparatus first used by van Eldik, and at the same 

 time with me by Hartman. The bath was constructed in a way 

 as described by me in a former paper and as it was used afterwards 

 by VAN Eldik. Whenever small fluctuations of temperature occurred 

 the observations were reduced to one and the same mean temperature 

 by making use of an approximated coefficient of temperature which 

 could be deduced from the uncorrected experiments. 



§ 3. TJie isotliermah. 



In table I the results of the determination of isotherinals arc 

 communicated. The pressure is expressed in atmospheres, the 

 volumes have been measured by taking as unit the theoretial volume, 

 viz. : the volume that would be occupied by the same quantity 

 of the mixture at a temperature of 0° C. and under a pressure of 

 1 atm., if it followed the laws of a perfect gas-;. 



The reduction to 0° C. was made by means of the coefficient of 

 expansion of carbonic acid 0,00371 ^), the reduction to 760 m.m. 

 by means of Boyle's law which in the range of pressures here 

 coming into account was sufficiently accurate. 



') loc. dt. 



2) For rurl.liur explaiiatiuii see a fullowiiig üoiiunuiUL'atiou. 



^) See u i'ollüwiii"- commuiiiciitiou. 



