THE 

 LONDON, EDINBURGH, and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



[FOURTH SERIES.] 



JULY 1867. 



I. Method of determining the Specific Gravity of Vapours and 

 Gases. By R. Bunsen, F.R.S., $c* 



[With a Plate.] 



THE method of determining the specific gravity of gases and 

 vapours described in the following communication does 

 not depend upon any new principle, but, on the contrary, differs 

 from the mode usually employed only in practical details. The 

 object of this method is to attain the maximum amount of accu- 

 racy by the employment of the most convenient and simplest 

 experimental means and of the smallest number of observa- 

 tions. It depends, in the first place, upon the ready prepara- 

 tion- of glass vessels which possess equal capacities within one- 

 hundredth of a cubic centimetre, and whose weights are the 

 same to within a fraction of a milligramme ; secondly, upon the 

 employment of an unalterable perfectly air-tight stopper of very 

 simple construction, by means of which a vessel which has been 

 once for all weighed, may be used as frequently as may be wished 

 for the determination of the specific gravity of gases and vapours; 

 and thirdly, upon the possibility of arranging an air-bath of tole- 

 rably large dimensions in which almost perfectly constant tem- 

 peratures can be kept up for any desired length of time. 



In order to prepare vessels of equal weight and capacity, a 

 number of large glass tubes (numbered with a diamond) are 

 melted off a tube having a diameter of 25 millims. and a thick- 

 ness of 1*3 millim., and one end of each tube is rounded in the 

 flame. Each tube is then partly filled with an equal volume of 



* Translated by Prof. Koscoe, F.E.S., from Annakn der Che?nie und Phar- 

 macie, vol. cxli. p. 273. 



Phil Mag. S. 4. Vol. 34, No. 227. July 1867. B 



