92 CARBONIC ACID GAS. 



The remaining supporter, Bromine, was very briefly no- 

 ticed; and the obvious distinctions between the four support- 

 ers of combustion then stated, forTeadiness of remembrance, as 

 follows : " OXYGEN is a colourless and invisible gas , CHLO- 

 RINE is a greenish yellow gas ; IODINE is a solid body ; and 

 BROMINE is a liquid substance." Some explanatory remarks 

 on Chemical nomenclature, or the system of expressive names 

 given to the bodies which it is the object of chemistry to 

 examine, suggested by the compounds of supporters with 

 other bodies, named Oxides, Chlorides, Iodides, and Bromides, 

 concluded the history of the Simple Supporters of Combus- 

 tion. 



The relations of atmospheric air to combustion, and the sim- 

 ple substances analogous to Oxygen, that constituent of the air 

 which supports combustion, having thus been fully examined ; 

 its relations to respiration were next entered into, in order to 

 complete its history. For this purpose it became necessary 

 to impart some knowledge of another gaseous body, Carbonic 

 acid gas. 



The simple combustible Carbon being stated to be the princi- 

 pal constituent of all the substances commonly used as fuel 

 or for the purpose of obtaining heat by their combustion 

 wood, charcoal, common or mineral coal, and coke, were 

 exhibited, as being chief sources or more or less pure varieties 

 of carbon ; the existence of that body in a crystallized and 

 absolutely pure form, in the Diamond, being also mentioned. 

 The experiment of burning charcoal in oxygen gas was made, 

 in exemplification of the truth, that, when any of the bodies 

 just named are burnt, either in the air, or in mere oxygen, 

 the carbon they contain unites to the oxygen present, and be- 

 comes carbonic acid gas ; thus exchanging the solid for the 

 aeriform or gaseous state. The attention of the pupils was 

 then particularly directed to the fact, on account of its im- 

 portance in the chemistry of respiration, that, in this process, 

 six parts of carbon, by weight, combine with sixteen of oxygen, 

 and become twenty-two of carbonic acid, without increasing 

 the bulk of the oxygen. 



The ordinary mode of obtaining this aeriform substance for 

 the purpose of experiment, by expelling it from pounded mar- 

 ble, or chalk, or any other variety of the earthy salt called 

 carbonate of lime, by means of dilute muriatic acid, was next 

 exhibited, and the theory of the operation explained, as was 

 done in all cases of this nature. The properties of this gas, 

 especially its great weight, and its power of extinguishing burn- 

 ing bodies, were experimentally illustrated ; and the subject 

 was concluded by an account of its mode of action in destroy- 



