80 Royal Society: — Dr. Andrews on the Physical 



I have been gratified to find that the two results (for 13 o, 09 

 and 21°-46) recorded in my former paper are in close agreement 

 with these later experiments. On the other hand, the pressures 

 I have found are lower than those given by Eegnault as the result 

 of his elaborate investigation (Memoires de l'Academie des Sci- 

 ences, vol. xxvi. p. 618). The method employed by that distin- 

 guished physicist was not, however, fitted to give accurately the 

 pressures at which carbonic acid gas liquefies. It gave, indeed, the 

 pressures exercised by the liquid when contained in large quantity 

 in a Thilorier's reservoir ; but these pressures are always con- 

 siderably in excess of the true pressures in consequence of the 

 unavoidable presence of a small quantity of compressed air, although 

 the greatest precautions may have been taken in filling the appa- 

 ratus. Even -g-J-y part of air will exercise a serious disturbing 

 influence when the reservoir contains a notable quantity of liquid. 



Law of Boyle. — The large deviations in the case of carbonic 

 acid at high pressures from this law appeared distinctly from 

 several of the results given in my former paper. I have now 

 finished a long series of experiments on its compressibility at the 

 respective temperatures of 6°*7, 63°*7, and 100° Centigrade. The 

 two latter temperatures were obtained by passing the vapours 

 of pyroxylic spirit (methyl alcohol) and of water into the rect- 

 angular case with plate-glass sides in which the tube containing 

 the carbonic acid is placed. The temperature of the vapour of 

 the pyroxylic spirit was observed by an accurate thermometer, 

 whose indications were corrected for the unequal expansion of the 

 mercury ; while that of the vapour of water was deduced from 

 the pressure as given by the height of the barometer and a 

 water-gauge attached to the apparatus. At the lower tempera- 

 ture (6 0, 7) the range of pressure which could be applied was 

 limited by the occurrence of liquefaction ; but at the higher tem- 

 peratures, which were considerably above the critical point of 

 carbonic acid, there was no limit of this kind, and the pressures 

 were carried as far as 223 atmospheres. I have only given a few 

 of the results ; but they will be sufficient to show the general 

 effects of the pressure. In the following Tables p designates the 

 pressure in atmospheres as given by the air-manometer, t' the 

 temperature of the carbonic acid, e the ratio of the volume of the 

 carbonic acid under one atmosphere and at the temperature t' to 

 its volume under the pressure jo r and at the same temperature, and 

 the volume to which one volume of carbonic acid gas measured at 

 0° and 760 millimetres is reduced at the pressure jp and tempera- 

 ture t'. 



