374 PRINCIPLES OF CHEMISTRY 



a part of the carbonic anhydride is transformed into a solid snowy 

 mass. Water, mercury, and many other liquids freeze on coming into 

 contact with snowlike carbonic anhydride. 9 In this form carbonic 

 anhydride may be preserved for a long time in the open air, because it 

 requires still more heat to turn it into a gas than when in a liquid 

 state. Solid carbonic anhydride, notwithstanding its very low tempera- 

 ture, can be safely placed on the hand, because it constantly evolves gas 

 which prevents its coming into actual contact with the skin ; but if a 

 piece be squeezed between the fingers, it produces a severe frost bite 

 similar to a burn. If the snowlike solid be mixed with ether a semi- 

 liquid mass is obtained, which may be used for artificial refrigeration. 

 This mixture may be used for liquefying many other gases such as 

 chlorine, nitrous oxide, hydrogen sulphide, and others. The evapora- 

 tion of such a mixture proceeds with far greater rapidity under the 

 receiver of an air-pump, and consequently the refrigeration is more 

 intense. By this means many gases may be liquefied which resist 

 other methods namely, olefiant gas, hydrochloric acid gas, and others. 

 Liquid carbonic anhydride in this case congeals in the tube into a 

 glassy transparent mass. Pictet availed himself of this method for 

 liquefying many permanent gases (see Chap. II.). 



The capacity which carbonic anhydride has of being liquefied stands 

 in connection with its solubility in considerable quantity in water, 

 alcohol, and other liquids. Its solubility in water has been already 

 spoken of in the first chapter. Carbonic anhydride is still more soluble 

 in alcohol than in water, namely at one volume of alcohol dissolves 

 4'3 volumes of this gas, and at 20 2'9 volumes. 



Aqueous solutions of carbonic anhydride, under a pressure of several 

 atmospheres, are now prepared artificially, because water saturated 

 with this gas is a good means of promoting digestion and quenching 

 thirst. For this purpose the carbonic anhydride is pumped by means 

 of a force pump into a closed vessel containing the liquid, and then 

 bottled off, taking special means to ensure rapid and air-tight corking. 

 Various effervescing drinks and artificially effervescing wines are thus 

 prepared. The presence of carbonic anhydride has an important 



9 When a fine stream of liquid carbonic anhydride is discharged into a closed metallic 

 vessel, about one-third of its mass solidifies and the remainder evaporates. In employing 

 solid carbonic anhydride for making experiments at low temperatures, it is best to use it 

 mixed with ether, otherwise there will be few points of contact. If a stream of air be 

 blown through a mixture of liquid carbonic anhydride and ether, the evaporation proceeds 

 rapidly, and great cold is obtained. At present in some special manufactories (and for 

 making artificial mineral waters) carbonic anhydride is liquefied on the large scale, poured 

 into wrought-iron cylinders provided with screwed taps, and in this manner it can be 

 transported and safely preserved for a long time. 



