of the Argillaceous Iron- Ore. 281 



in its composition besides the expulsion of carbonic acid. 

 Thus if it contains any bituminous or coally matter, or iron 

 pyrites, the volatilizable portion of these will be driven off by 

 the heat. The small portion of water which the ore generally 

 contains will also be expelled. AH these circumstances tend 

 to make the quantity of carbonic acid appear greater than it 

 is in reality. On the other hand, it is necessary to remark, 

 that these irregularities are counterbalanced to a certain extent 

 by another decomposition which always takes place during the 

 ignition of an ironstone, and whose tendency is to make the 

 quantity of carbonic acid appear less than it is in reality. 

 When the carbonate of protoxide of iron is ignited, a reaction 

 always ensues between its constituents, the protoxide of iron, 

 in consequence of its disposition to unite with an additional 

 dose of oxygen, attracts that principle from a portion of the 

 carbonic acid, reducing it to the state of carbonic oxide gas, 

 and becoming itself converted partially into peroxide. This 

 decomposition evidently introduces a double error into the re- 

 sults ; for the ponderable matter that is abstracted from the 

 carbonic acid is superadded to the oxide of iron. The decom- 

 position of the carbonic acid, and the consequent peroxidation of 

 the protoxide of iron take place to a much smaller extent in 

 those cases where the ore is suddenly exposed to a pretty strong 

 red heat, than in those where the ignition is brought on very 

 gradually. 



If it be desirable to ascertain by the most exact method, the 

 amount of carbonic acid contained in any one ore, this is done 

 by dissolving it in an acid. The process may be conducted in 

 the following manner. Procure a globular-shaped glass bot- 

 tle, having a cylindrical neck about an inch in length, * and 

 adapt to it a stopper made by rolling up very loosely a bit of 

 open textured woollen cloth, (flannel for example.) Fill the 

 bottle half full with a dilute muriatic acid, prepared by mix-, 

 ing one part of the concentrated acid with one part and a half 

 of water. The acid should be introduced by means of a small 

 funnel, as it is of some consequence that the inside of the neck 

 of the bottle should be kept quite dry. Then replace tlie 



* Any person accustomed to the management of a table- blowpipe, may 

 easily form a bottle of this kind with a piece of barometer tube. 



