on the Atomic Weight of Carbon. 211 



original weight of the matter submitted to combustion. In 

 the analyses we possess of naphthalin by Mitscherlich, by 

 Dumas, and by Woskresensky, this is particularly remarkable. 

 One hundred parts of naphthalin gave to Mitscherlich, — 



1. 2. 



Carbon 94-34 94-440 



Hydrogen 6*26 6-225 



100-60 100-665 



One hundred parts of naphthalin gave to Dumas, — 



1. 2. 3. 4. 5. 



Carbon ... 94-2 94-22 94-27 94-9 94-9 

 Hydrogen 6-3 6-30 6-26 6-2 . 6'1 



100*5 100-52 100-53 101-1 101*0 



And to Woskresensky, 100 parts of the same substance 

 yielded — 



1. 2. 3. 4. 5. 6. 



Carbon 94*625 94-598 95-0268 93-668 94*395 94'494 

 Hydrogen 6*528 6*289 5-3830 6*142 6-206 6-526 



101-153 100*897 100-4098 99-810 101*601 101*020 



This constant occurrence in so many carefully conducted 

 experiments, indicates a common source of error upon which 

 it is dependent ; it can only be attributed to two causes. 

 One of these may be sought in the defects of the method of 

 analysis, the other in the supposition that the products of the 

 combustion (water and carbonic acid) have different compo- 

 sitions from those usually assigned to them. If indeed either 

 water or carbonic acid contains somewhat less of hydrogen 

 or of carbon than we at present suppose, then as we calculate 

 from the quantities found of the former bodies, the excess in 

 the analyses is diminished in the same proportion. 



Let us suppose, for example, that carbonic acid contains 

 only 76 carbon instead of 76*437 to 200 of oxygen, and water 

 only 12 hydrogen instead of 12-4795 to 100 oxygen, and 

 then we shall have no excess in any of the analyses quoted, 

 whilst the experimental come to agree perfectly with the cal- 

 culated results. Are we then entitled to make such changes 

 in the atomic weights, proceeding as we do upon the assumed 

 accuracy of experiments, which, from the complex nature of 

 the apparatus, can make no claim to absolute precision ; or 



P2 



