368 



CARBONIC ACID. 



(e.) Carbonic acid, contained in carbonate of lime, or of soda, is 

 decomposed by phosphorus, and the carbon appears in the form of 

 charcoal. 



(/.) It is done by taking a glass tube J of an inch wide, and 20 

 inches long; it is sealed at one end, and coated with sand and clay, 

 to within an inch of the end ; phosphorus is placed there, and mar- 

 ble powder, or better, carbonate of soda, dried in a sufficient heat ; 

 the part containing the carbonate is heated red hot, and then the 

 phosphorus is sublimed through it, and the heat continued for some 

 minutes ; charcoal is found mixed with a phosphate.* 



(g.) In Dr. Pearson's experiment, 200 grains of phosphorus, and 

 800 carbonate of soda, gave 40 grains charcoal. f 



(A.) If phosphorus be boiled in a solution of carbonate of soda, it 

 becomes black in consequence of the developement of charcoal ; it 

 is done in a small flask, and the process occupies an hour. 



4. PROPERTIES. 



(a.) Carbonic acid gas is fatal to animal life ; if we confine a 

 mouse or other small animal in this gas, it will speedily die. But- 

 terflies and other insects may be killed in this manner, or hy heat 

 alone, without injuring their beauty. This gas kills both by suffoca- 

 tion and by a deadly influence of its own. 



(b.) It extinguishes combustion ; lower a pendent candle into it, 

 and withdrawing it immediately, drop it into oxygen gas ; it is ex- 

 tinguished and relighted alternately. Gun powder burns in this gas.f 



from a small gazometer. A tray of platinum, with a lump of potassium, is slipped 

 into the flask, taking care at the same time, not to let in the air or spill the carbon- 

 ic acid; a tube, twice bent at right angles, is then adapted, and dips into a glass 

 containing mercury ; live coals are applied beneath the tray of potassium, and 

 just at the point of the fusion of plate glass, the potassium 

 inflames with bright light, regenerated potassa fills the 

 flask with white fumes, and charcoal precipitates, mix- 

 ed with the potassium. A green flask would probably be 

 better, as enduring more heat ; sometimes the experi- 

 ment succeeds with difficulty, and the bottom of the flask 

 is indented. N. B. The second tube and the mercury 

 may be dispensed with, provided we cork the flask rath- 

 er loosely, so as to allow the gas to escape a little by ex- 

 pansion. 



* Phil. Trans. 1791, p. 182. 



t Phil. Trans. 1792, p. 289. 



t A, Large gJass globe with a wide neck filled with 

 carbonic acid gas. 



6, Iron or copper spoon with gun powder in it. 



C, An iron rod heated red hot at the lower end to in- 

 flame a few grains of gunpowder. 



d, Orifice stopped with a cork, which being with- 

 drawn, the gas runs in a visible current and fluctuates. 



A candle cannot burn in atmospherical air, containing 

 one fourth part, by measure, of carbonic acid. 



