72 THE ATOMIC WEIGHTS. 



CARBON. 



Although there is a large mass of material relating to the atomic weight 

 of carbon, much of it may be summarily set aside as having no value 

 for present purposes. The density of carbon dioxide, which has been 

 scrupulously determined by many investigators,* leads to no safe esti- 

 mate of the constant under consideration. The numerous analyses of 

 hydrocarbons, like the analyses of naphthalene by Mitscherlich, Wosk- 

 resensky, Fownes, and Dumas, give results scarcely more satisfactory. 

 In short, all the work done upon the atomic weight of carbon before the 

 year 1840 may be safely rejected as unsuited to the present requirements 

 of exact science. As for methods of estimation we need consider but 

 four, as follows : 



First. The analysis of organic salts of silver. 



Second. The determination of the weight of carbon dioxide formed by 

 the combustion of a known weight of carbon. 



Third. The method of Stas, by the combustion of carbon monoxide. 



Fourth. From the density of carbon monoxide. 



The first of these methods, which is probably the least accurate, was 

 employed by Liebig and Redtenbacher f in 1840. They worked with 

 the acetate, tartrate, racemate, and malate of silver, making five ignitions 

 of each salt, and determining the percentage of metal. From one to 

 nine grammes of material were used in each experiment. 



In the acetate the following percentages of silver were found : 



64.615 

 64.624 

 64.623 

 64.614 

 64.610 



Mean, 64.6172, .0018 



After applying corrections for weighing in air, this mean becomes 

 64.6065. 



In the tartrate the silver came out as follows : 



59.297 

 59-299 

 59-287 

 59-293 

 59-293 



Mean, 59 2938, .0014 

 Or, reduced to a vacuum, 59.2806 



* Notably by Lavoisier, Biot and Arago, De Sauss'ure, Dulong and Berzelius, Buff, Von Wrede, 

 Regnault, and Marchand. For details, Van Geun's monograph may be consulted, 

 f Ann. Chem. Pharm., 38, 137. Mem. Chem. Soc., i, 9. Phil. Mag. (3), 19, 210. 



