CH. XXVII. BLACK'S 'FIXED AIR.' 22'/ 



water, which was not enough to account for the loss of 

 weight. 



At last he remembered that Dr. Hales had driven air out 

 of substances, and collected it in bottles ; and he began to 

 consider whether the heat of burning might not have driven 

 some heavy kind of air out of the limestone, and so made it 

 lighter. To prove this he made the experiment which has 

 since been always used for making small quantities of car- 

 bonic acid gas. He put some pieces of limestone in the 

 bottle, a, Fig. 38, and poured upon them some water and 



Carbonic Acid rising from Limestone and Acidulated Water (Griffm). 



B, Bottle containing pieces of limestone in water and acid, b. Connecting tube. 



c. Inverted jar, out of which the rising gas is driving the water. 



some acid. He then stopped the bottle with a tight cork, 

 and joined it by the tube ^ to a large glass jar, Cy filled with 

 water, and standing with its open end downwards in a 

 vessel of water. In a few moments the bubbles began to 

 rise from the limestone, and passing into the jar, q drove 

 out the water and filled the jar with gas. 



This gas Black called * fixed air,' because it had been 

 fixed in the Hmestone before it was driven out by the 

 acid. He collected and weighed it, and found that it exactly 



