ATOMIC WEIGHTS 



65 



The effect of this combination is to give the work of Van der Plaats 

 overwhelming weight, to which it is perhaps not entitled. The other de- 

 terminations practically vanish. 



According to Scott ' all of the foregoing determinations are subject to 

 an important correction, namely, a reduction to weight in vacuo. This 

 correction was applied by Van der Plaats, at least partially; but Scott 

 lays emphasis upon the change in volume of the potash solution in which 

 the carbon dioxide was absorbed and weighed. The corrections, as ap- 

 plied by Scott, are given in the following table, in which the total reduced 

 weights of carbon and dioxide are used instead of the individual weights 

 of the separate experiments : 



Total C. Total CO.. Ratio. Atomic weight. 



Dumas and Stas 16.1994 59.4201 2.66804 11.9938 



Brdmann and Marchand.. 12.1636 44.58537 2.66547 12.0054 



Roscoe 6.4428 23.6275 2.66727 11.9973 



Friedel 1.33185 4.8818 2.66543 12.0056 



Van der Plaats 62.5115 229.1836 2.66630 12.0017 



If to these figures we assign the relative weights given in the previous 

 combination, the final mean will be identical with that of Van der Plaats 

 as before, and C = 12.0017, ± .0005. Scott adopted the unweighted average 

 of the five series given above, and made C = 13.0008. 



The second method for determining the atomic weight of carbon was 

 employed by Stas ^ in 1849. Carefully purified carbon monoxide 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 weigh- 

 ings were reduced to a vacuum standard, and in each experiment 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 determining the 

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

 the weights given by Stas, represent the quantity of carbon monoxide cor- 

 responding to one gramme of oxygen : 



.00005 



1 Journ. Chem. Soc, 71, 550. 1897. 



2 Bull. Arad. Belg., 1849 (1), 31. Oeuvres Completes, 1, 287. 



