atid on the^ Nature of the Diamond. 221 



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 error, we subjected our charcoal to a red heat 

 immediately before using it, 4nd also weighed it as speedily 

 as possible ; in fact while it was still warm. It may be pro- 

 per to state, that our weights were such as we could tho- 

 roughly depend upon. 



The volume of gas being so much influenced by tempera- 

 ture and pressure, these were noted during every experimentj 

 and thermometer 60'' Fahrenheit, barometer 30°, were as- 

 sumed as the standard. Gay Lussac remarks, that from 32° 

 to 2 12" Fahrenheit, dry air expands 0-00208, or ^J-part of 

 its bulk for every degree of the thermometer. Dalton make? 

 it 0*000207, or ^i^ part ; we therefore divided the whole 

 quantity of gas by 480, and multiplied the quotient by the 

 degrees of difference under 60". 



It being of great consequence in these experiments to 

 know the exact weight of a given quantity of oxygen and 

 carbonic acid gases, we resolved to examine for ourselves, 

 whether the statements already given were quite correct, 

 and accordii:gly made carbonic acid over mercury from 

 Carrara marble and diluted sulphuric acid, which being 

 tried with lime water in Pcpys's eudiometer, was all ab- 

 sorbed in 3 minutes except 1 part in 100. We used two 

 charo-es of lime water^ though one would have been suffi- 

 cient. 



A glass globe being exhausted by an excellent air pump, 

 was exactly balanced on a beam sensible to a minute portion 

 of a grain ; then being screwed upon one of the e;lass re- 

 , ceivers of the mercurial gasometer previously filled with 

 carbonic acid gas, 21 cubic inches entered. The globe was 

 now increased in weight by 10*2 grains. In order to be cer- 

 tain we repeated the experiment, with exactly the same re- 

 i'llts. The 21 cubic inches were to be brought to the mean 

 temperature and pressure, as the thermometer stood at 44* 

 Fahrenhcltj the barymctcr 29-66. 



21 



