38 
acid contained to 44 of carbon 112 of oxygen, being just 
double of that in the carbonic oxide. Dalton adds, “ this 
most striking circumstance seems to have wholly escaped 
their notice.” Hence Dalton assumed that one atom of 
carbon is united in the case of carbonic oxide with one atom 
of oxygen, whilst carbonic acid possessed the more compli- 
cated composition and contains two atoms of oxygen to one 
of carbon. How if carbonic acid contains carbon and 
oxygen in the proportion of 28 to 72, carbonic oxide must 
contain half as much oxygen, viz., 28 of carbon to 36 of 
oxygen, and assuming that the atomic weight of oxygen is 
5 ’5 that of carbon must be 
28 X 5‘5 
36 
:4-3. 
Having thus 
arrived at the number 4*3 as the first atomic weight of 
carbon, it is easy to see why Dalton gave 6*3 as the atomic 
weight of carburetted hydrogen from stagnant water, and 
5-3 as that of olefiant gas. The one represents 1 atom 
of carbon to 2 of hydrogen, the other 1 of carbon to 1 of 
hydrogen, or olefiant gas contains two equal quantities of 
carbon, only half as much hydrogen as marsh gas. This 
conclusion doubtless expressed the results of Dalton s own 
experiments upon these two gases which were made, as we 
know from himself, in the year 1804. He proved that 
neither of these gases contains anything besides carbon 
and hydrogen, and ascertained — by exploding with oxygen 
in a Yolta’s Eudiometer — that if we reckon the carbon in 
each the same, then carburetted hydrogen contains exactly 
twice as much hydrogen as olefiant gas does, and that '‘just 
half of the oxygen expended on its combustion was applied 
to the hydrogen and the other half to the charcoal. This 
leading fact afibrded a clue to its constitution.” Whereas, 
in the case of olefiant gas, two parts of oxygen are spent 
upon the charcoal and one part upon the hydrogen. 
The atomic weight of nitrogen (azote =4‘2) was doubtless 
obtained from the consideration of the composition of am- 
monia, whose atomic weight is given in the table at 5*2. 
