Liquefactioti and Solidification of Carbonic Acid. 351 



to which 24 fluid ounces of water are to be added. After ma- 

 king these into a thin paste by stirring, 9 fluid ounces of com- 

 _ mon sulphuric acid are to be poured into the copper cup, N, and 

 that is to be let down by a crook of wire into the generator. 

 After the screw, E, has been firmly applied, and the stop-cock, 

 J, closed, the contents of the generator are to be brought into ad- 

 mixture by moving it round to a horizontal position on the swivel 

 D, which is supported by the wooden frame, B, B. There is a 

 check bar at C. This motion is to be repeated several times. In 

 about ten minutes the whole of the carbonic acid is liberated, 

 and exists in A, chiefly in a liquid state. 



The next step in the process is to attach, by means of the stir- 

 rup and screw, K, K, the receiver, F, previously cooled by ice. 

 The keys, I and J, may then be opened slowly, and instantly the 

 liquid carbonic acid is perceptible in the gauge, L. At the end 

 of ten minutes, the communication with the generator may be 

 cut ofl" — when about eight fluid ounces of liquid acid at 32° F. 

 will be found in the receiver. 



By letting this liquid into the box, O, through the pipe, G, a 

 large part of it is instantly expanded into gas, which escapes 

 through the tube, P. The coldness consequent on the enormous 

 expansion, freezes another part of the liquid, which falls to the 

 bottom of O. About one drachm of solid matter is thus formed 

 for each ounce of liquid. 



The porosity and volatile character of the solid render its spe- 

 cific gravity of difficult ascertainment. When recently formed, it 

 is about the weight of carbonate of magnesia, and when strongly 

 compressed by the fingers, its density is nearly doubled. Solid 

 carbonic acid is of a perfect whiteness, and of a soft and spongy 

 texture, very like slightly moistened and aggregated snow. It 

 evaporates rapidly, becoming thereby colder and colder, but the 

 coldness produced seems to steadily lessen the evaporation, so 

 that the mass may be kept for some time. A quantity weighing 

 346 grains lost from 3 to 4 grains per minute at first, but did not 

 entirely disappear for three hours and a half. The natural tempe- 

 rature was from 76° to 79°. The solid is most easily kept when 

 compressed and rolled up in cotton or wool. Its temperature 

 when newly formed is not exactly ascertainable, because it is im- 

 mediately lowered by evaporation. Thilorier seems to have en- 

 tertained the opinion, that the greatest degree of cold was created 



