ANNALS 



OF 



PHILOSOPHY. 



SEPTEMBER, 1820. 



Article I. 

 On the Specific Gravity of Gases. By T. Thomson, M.D. F.R.S. 



JN the preceding volumes of the Annals of Philosophy I have 

 more thaa once drawn the attention of my readers to this impor- 

 tant subject. I have given two different tables of the specific 

 gravity of gases constructed from the experiments which 1 con- 

 sidered to be the most accurate, and J have likewise inserted a 

 table drawn up by M. Gay-Lussac, which I have reason to believe 

 has been very generally followed by French chemical writers ; 

 indeed probably by the greater number of continental chemists. 

 But the very great importance of determining these specific 

 gravities with precision made me anxious to have it in my power 

 to go over the experiments in my own laboratory. This has. 

 been fortunately accomplished chiefly in consequence of my 

 removal to the university of Glasgow. The balance which I 

 employed was sensible to the thousandth part of a grain, even 

 when loaded with my weighing flask. Eveiy attention was paid, 

 to the purity of the gases subjected to experiment; and to pre- 

 vent inaccuracies from accidental and unforeseen sources every 

 experiment was repeated at least three times ; and, in general, 

 we did not rest satisfied while a discrepancy existed between 

 two experiments amounting to one thousandth part of the whole 

 weight. I need not describe the method which I followed, as an 

 account of it has been already given in a former volume of the 

 Annals of Philosophi/. It is simple and easy, and founded upon 

 a well-known property of gases. It saves the trouble of the 

 Vol. XVI. N° III. L 



