Note 9 bis — Chapter IX · COMPOUNDS OF CARBON WITH OXYGEN AND NITROGEN

Solid carbonic anhydride, notwithstanding its very low temperature, can be safely placed on the hand, because it continually 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 snow-like solid be mixed with ether, a semi-liquid mass is obtained, which is employed for artificial refrigeration. This mixture may be used for liquefying many other gases—such as chlorine, nitrous oxide, hydrogen sulphide, and others. The evaporation 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 Chapter II.)

Bleekrode, by compressing solid CO₂ in a cylinder by means of a piston, obtained a semi-transparent stick, which contained as much as 1·3 and even 1·6 gram of CO₂ per cubic centimetre. In this form the CO₂ slowly evaporated, and could be kept for a long time.