374 CARBONIC ACID. 



(/.) Lime or barytic water is precipitated by blowing through it 

 with a tube ; or by agitation in air which has been breathed. 



7. COMBINING WEIGHT. The weight of carbon is 6, and carbonic 

 acid being a compound of 2 proportions of oxygen, and 1 of carbon, 

 its equivalent will be 16-f-6=22. 



In volumes, Gay-Lussac estimates it constitution to be 1 gaseous 

 carbon, and 1 oxygen, condensed into 1 volume. As oxygen under- 

 goes no change of volume, by combining with carbon, and as 100 cu- 

 bic inches of carbonic acid weigh 46.597 grains, it follows that the 

 amount of carbon in vapor will be 46.59733.888, the weight of 

 100 cubic inches of oxygen, =12.709 grs. of carbon ; and as 12.709 

 : 33.888 : : 6 to 16, and 6 being the combining proportion of car- 

 bon, it follows that carbonic acid is composed as above. * 



8. POLARITY. Like other acids, it is evolved at the positive pole, 

 and is therefore electro negative. 



9. LIQUEFACTION OF CARBONIC ACID. 



Mr. Faraday\ effected this by cold and pressure. He contrived 

 to extricate the carbonic acid gas from sulphuric acid and carbonate 

 of ammonia, brought together at the moment, and after the bent glass 

 tube in which they were contained was sealed, the other end of the 

 tube was kept cold by a freezing mixture, and the gas, subjected to 

 its own enormous pressure, aided by cold, became fluid. These ex- 

 periments are very hazardous, as it is a more difficult gas to con- 

 dense than any with which Mr. Faraday succeeded ; very strong 

 tubes were required and yet they often exploded. 



10. PROPERTIES. 



(a.) Limpid, colorless, very fluid ; floating on the other fluids in 

 the tube ; distils readily and rapidly between and 32 ; refractive 

 power less than that of water, not altered by increase of cold. 



When it was attempted to open the tubes, they always burst with 

 powerful explosions ; at 32 the pressure was equal to 36 atmos- 

 pheres. 



Sir H. Davy, in a communication to the Royal Society, suggested 

 the application of condensed gases as a moving force, capable of be- 

 ing increased or diminished by slight variations of temperature. It 

 would be necessary only to let loose a little of the condensed carbonic 

 acid, to produce a powerful movement ; condensed nitrogen would 

 be still more powerful, and hydrogen would exert a tremendous force. 

 No furnaces would be necessary, but mere variations between sun- 

 shine and shade might perhaps be sufficient to vary the energy of the 

 power. It is obvious, however, that the danger of explosion would 

 be great. 



11. DISCOVERY. Dr. Black discovered carbonic acid in 1755, or 

 6, and thus laid the foundations of the pneumatic chemistry; he called 



* Turner. t Phil. Trans. 1823, p. 193. 



