CARBONIC OXIDE. 395 



(e.) During the disengagement of the gas, die powder seems as if 

 boiling, and is said to emit, towards the end, a bluish phosphoric light.* 



Remark. The above described salt has been regarded as a bi- 

 carbonate, but Dr. Henry is of opinion, from his own analysis and 

 from that of Berzelius, that it is a hydrated carbonate and that its 

 composition is 



1 equivalent of magnesia, - 20 28.60 



1 do. carbonic acid, - - 22 32. 



3 do. water, - 27 39.40 



Its equivalent 69 100.00 



It appears that, although the anhydrous carbonate has been found 

 native, (see note p. 392,) it has not yet been formed by art. 



Berzelius has formed a carbonate of magnesia and potassa, by 

 mingling bi-carbonate of potassa and muriate of magnesia. It seems 

 to be of little importance, f 



3. MISCELLANEOUS. ~/w the arts, the carbonate of magnesia is pre- 

 pared from the bittern of the salt pans, remaining from the crystalli- 

 zation of common salt, which contains much muriate and sulphate of 

 magnesia. Carbonate of either of the alkalies, by double exchange, 

 affords carbonate of magnesia, whose precipitation is hastened by 

 boiling. 



4. USES. As an antacid and cathartic. (See magnesia, p. 273.) 

 On account of the flatulency sometimes produced by the carbonate 

 of magnesia, calcined magnesia is used. Dr. Black says that it 

 is liable to contain a portion of quick lime, derived from the sul- 

 phate of lime of the bittern. No other earth has cathartic powers ; 

 most of the rest are austere and astringent, particularly lime. 



CARBONIC OR CARBONOUS OXIDE. 



1. HISTORY. Discovered by Dr. Priestley; who obtained it 

 from dry metallic oxides with dry charcoal, and thought it was, at 

 least in part, hydrogen, or that hydrogen entered into its composi- 

 tion ; it therefore revived, for a season, the once favorite notion of a 

 phlogistic f principle in the metals, charcoal, &c. and an animated con- 



* Four. IV. 67. t Edin. Phil. Jour. II. 67, and Henry, I. 619. 



t I happened to be in Philadelphia, as a pupil of Dr. Woodhouse, in the winter of 

 1802-3, when Dr. Priestley, who, as is well known, passed the latter years of his life 

 in Pennsylvania, came in person, to the laboratory of Dr. Woodhouse, who was 

 himself a disciple of Lavoisier, and who performed various experiments on this topic, 

 at that time keenly controverted. It was the last effort to sustain the doctrine of 

 phlogiston, and to produce from metals and inflammables a real substance, to which 

 it was supposed that the name of phlogiston could be applied. Hydrogen had been 

 before called phlogiston, but it was impossible to prove its existence in all inflammable 

 bodies and metals, (unless the discovery of this gas should establish it,) and it was 

 distinctly proved that it forms water by its combustion. Indeed Dr. Priestley was 

 one of the first to perform that interesting experiment, but he did not eventually ad- 

 mit the conclusion. 



