78 THE ATOMIC WEIGHTS. 



reduced to vacuum standards. The data, with ash deducted, are sub- 

 joined: 



Mean, 2.6660, ± .0001 



This combines with the previous series thus : 



Dumas and Stas, first set 2.6683, zh .0005 



^ Dumas and Stas, second set 2.66985, zh .0013 



Dumas and Stas, third set 2.6665, =t .0007 



Erdmann and Marchand, first set 2.6636, ±: .0007 



Erdmann and Marchand, second set 2.6637, zb .0009 



Roscoe 2.6654, d= .0006 



Friedel 2.6634, ± .0004 



Van der Plaats 2.6660, zfc .0001 



General mean 2.6659, zb .0001 



Another very exact method for determining the atomic weight of car- 

 bon was emploj^ed by Stas* in 1849. Carefully purified carbon mo- 

 noxide was passed over a known weight of copper oxide at a red heat, 

 and both the residual metal and the carbon dioxide formed were weighed. 

 The weighings were reduced to a vacuum standard, and in each experi- 

 ment a quantity of copper oxide was taken representing from eight to 

 twenty-four grammes of oxygen. The method, as will at once be seen, 

 is in all essential features similar to that usually employed for determin- 

 ino- the composition of water. The figures in the third column, deduced 

 from the weights given, by Stas, represent the quantity of carbon mo- 

 noxide corresponding to one gramme of oxygen : 



.00005 



For the density of carbon monoxide the determinations made by 

 Leducf are available. The globe used contained 2.9440 grm. of air. 



* Bull. Acad. Bruxelles, 1849 (i), 31. 

 tCorapt. Rend., 115, 1072. 1S93. 



