Notices respecting New Books. 4^9 



at which the operation is carried on, the density of carbonic acid 

 bears a different proportion to that of atmospheric air, although in 

 each case, as it is scarcely necessary to mention, care has been 

 taken to bring the air to the same temperature and the same pressure. 

 The following are a few figures in support of this conclusion : — 

 The density of carbonic acid gas at 0° is — 



Under the pressure of 760-00 millims. 1-52910 

 374-13 .. 1-52366 

 22417 .. 1-52145 

 The density of the same gas at 100° is — 



Under the pressure of 760-00 millims. 1*52418 

 383-39 .. 1-52410 



Hence it results, that the atomic weight of cgrbon. deduced from 

 the density of carbonic acid gas, varies according to that of the 

 densities selected. Thus the atomic weight of 75-000 admitted by 

 M. Dumas, conducts to the theoretical density of 1-52024 for 

 carbonic acid, a density very near to tliat found for this gas at 0°, 

 and under the pressure of 224-17 millims., while the density of 

 1-52910 ascertained for carbonic acid at 0° and under a pressure of 

 760 millims., conducts for the atomic weight of carbon to 76*60, a 

 number closely approximate to that of^ 76-44, for a long time 

 adopted by chemists on the authority of Berzelius. This example 

 shows the uncertainty which there is a risk of meeting in the deter- 

 mination of atomic weights deduced from the density of elastic fluids. 



The first researches of M. Regnault showed, then, that the law 

 of equality and uniformity of the dilatation of elastic fluids was not '\ 

 general, and that Mariotte's law seemed to be equally defective; as 

 we have already mentioned, other physicists had arrived at the same 

 result in regard to this last law, at least for gases capable of being 

 liquefied by high pressure. In his sixth memoir M. Regnault at- 

 tacks the question directly, and after a critical analysis of earlier 

 labours, passes to the description of his own experiments. They 

 were made by means of apparatus erected at the College of France, 

 in a special building, which had been constructed, at the request of M. 

 Savart, for hydraulic experiments, the execution of which was pre- 

 vented by the premature death of that skilful physicist. This building 

 consists of a square tower of two stories, the total height being 

 12'5 metres. A mercurial manometer is fixed in the inside against 

 a vertical wall, which is of the entire height of the building. A cast- 

 iron vessel, closed by a cylindrical reservoir, which serves as the 

 reservoir of mercury, is fitted with a cylindrical adapter bearing the 

 necessary tubulures, three of which are vertical ; a little hydraulic 

 force-pump serves to compress the air in the reservoir, with which 

 it communicates by a horizontal tubulure. For the experiments on 

 the compressibility of gases, the author used only two of the vertical 

 tubulures; the third was hermetically closed. He placed in them 

 two glass tubes, one of which, three metres high, communicated with 

 the apparatus which contained the air to be compressed, and the 



Phil. Mag. S. 3. Vol. 36. No. 240. Jan. 1 850. E 



