ON THE QUANTITY OF CARBON IN CARBONIC ACID. 221 



Grains. Total increase. Time. 



6 P.M. 44*5 — '5 38 4*5 24 hours. 



9 44*4 — '1 zz 4*4 27 hours. 



Next day. 



f past 8 A.M. 44*9 + '5 = 4*9 38f houfs. 



f past 1 P.M. 447 ~ *2 is 4*7 43 § hours. 



10 .•••• 44*5 — *2 = 4*5 52 hours. 



Hence charcoal seems to act as an hygrometer: its greatest Seems to acta* 

 increase was 5 grains on 40, or 12f per cent. And in order anhygromeier* 

 to ascertain to what the increase of weight was owing, we 

 put 27*25 grains of charcoal, which had been thus exposed, 

 into a small bottle and tube connected with a receiver stand- 

 ing in the mercury bath, the whole of the vessels being also Water expel- 

 filled with mercury, in order to exclude common air. Heat 

 applied by an Argand's lamp produced gas equal to about 

 half the bulk of the charcoal; but as soon as the temperature 

 of the mercury rose to 214° Fahrenheit, elastic fluid stream- 

 ed from every piece of charcoal, which quickly condensed, 

 and 1± inch of the tube was occupied with water. This 

 proved that our suspicion of the increase of weight being 

 principally attributable to water, was well founded. 



The result of these, and other experiments, plainly point- Hence certain 

 ed out the precautions which were necessary, in order to ob- nece^sarr* 18 

 tain an accurate result with charcoal; for if we had weighed 

 4 grains of the charcoal a few hours after it was made, we 

 should only in fact have had 3 '5 grains of real charcoal, and 

 our calculations would have been erroneous. To avoid this 

 source of errour, we subjected our charcoal to a red heat im- 

 mediately before using it, and also weighed it as speedily as 

 possible; in fact, while it was still warm. It may be proper 

 to state, that our weights were such as we could thoroughly 

 depend upou. 



The volume of gas being so much influenced by tempera- The volumeof 

 ture and pressure, these were noted during every experiment ; fenced by * 

 and thermometer Go Fahrenheit, barometer 30°, were as- temperature 

 sumed as the standard. Gay Lussac remarks, that from an ? ressure - 

 32° to 212° Fahrenheit, dry air expands 0-00209, Or ^ 

 part of its bulk for every degree of the thermometer. Dal- 

 ton makes it 0*00207, or 4 -| T part; we therefore divided 



the 



