CARBONIC OXIDE.- 7^ 



This gas is often found in the lower part of 

 caverns, wells, mines, and other subterranean 

 places. In mines it proves frequently fatal to the 

 miners, who call it the choke damp. Wells, or 

 similar places, which have been shut up for a long 

 time, should never be entered without first putting 

 down a lighted candle : if this is extinguished, it 

 is not safe to go down. There are some caverns 

 in which this gas is produced in so great a quantity, 

 that it runs out at the opening, like a stream of 

 water: this is particularly the case with the cele- 

 brated Grotto del Cane. A dog is suffocated 

 if it be held for a short time in the lower part 

 of the cavern, but the upper part is free from 

 this gas. 



Charcoal should never be burnt in rooms that 

 have no chimney, because the red hot charcoal 

 unites with the oxygen of the atmosphere, and 

 forms carbonic acid, which cannot escape. Some 

 melancholy accidents have happened from this 

 cause. This gas has also been called mephitic air, 

 from its suffocating quality. 



Carbonic acid combines with all the alkalies, and 

 with the alkaline earths, lime, magnesia, barytes, 

 and strontia. With these it forms a class of salts, 

 called carbo7iates. 



Carbon does not combine with any of the metals 

 except iron. This combination is the carburet of 

 iroiiy called also plumbago and black lead ; which, 

 however, contains only five per cent, of iron. 

 It is the substance used for making black lead 

 pencils. 



Carbonic Oiide. — This body is always gaseous. 

 It contains only half as much oxygen as carbonic 

 acid does. It is void of taste and smell, and 

 fatal to animal life. It is inflammable, burning 



