354 



owing to the mutual deviations of the various substances with regard 

 to the law of corresponding states. This is shown by the following 

 table containing various values of SB. 



Reduced temperature .644. 



mean reduced virial-coefficent ^ = — 1,12. 



t ^ 



ammonia^) —12° 0. —1.22 



methjl chloride ^) — 5 — 0.961 



isopentane^) 23.7 —1.02 



n. butane =*) 0.0 -1.04. 



Test of the impurity. The theoretical normal volume found 388.1 

 leads to a molar weight of 57.77. If we assume the admixture to 

 be ethane^ its amount maj be calculated from the molar weights 

 of ethane (30.05) and butane (58.08) : the amount of ethane would 

 appear to be I'/o • 



The above result respecting the nature of the admixture finds 

 confirmation in the boiling point of our butane. This point ( — 1°.0) "j 

 was derived from determinations of the vapour pressure in the 

 neighbourhood of 0° : 



Owing to the presence of a more volatile admixture (ethane) the 

 boiling point will be too low. In order to remove it to a certain 

 extent the butane was cooled in solid carbon dioxide and vapour 

 was pumped off. After this operation the vapour pressure at 0° was 

 again measured; it was now 1,035 atm. The boiling point has therefore 

 actually been raised : it now becomes — 0.8°. In repeating the same 

 operation a large portion of the vapour coming off was collected 

 in the bulb of the mercury pump. The pressure above the small 

 quantity of liquid left, appeared to have diminished to 1.027 atm., 



1) For these data we are indebted to Mr. G. Holst, whose results, which were 

 worked out in the Leiden Laboratory, will shortly be published as a thesis at 

 Zurich. 



2) Calculated from S. Young's data. 



^) Deduced from the above value of B- 



^) In Comm. 125 p. 4 by a clerical error the boiling point was given as —0.1°. 



