| 
———_ =. + 
ee ————————— 
ON COLLOID CHEMISTRY AND ITS INDUSTRIAL APPLICATIONS. 153 
dioxide between 0 and about 3 mm. of mercury, there is a series of 
intermediate stages in which there are progressively increasing 
concentrations of the bicarbonate and decreasing concentrations of 
carbonate. But the explanation of this fact lies in the electrolytic 
decomposition of the salt. The presence of more HOU; ions results 
in a rounding off of the corner of the curve owing to reduced 
ionization of the salt. Again, there are some dyes which may exist 
in a reduced form, capable of taking up oxygen when exposed to the 
air. Experiments made by W. A. Osborne (not yet published) were 
unable to discover any one of these which was not either completely 
reduced or completely oxidized, as the phase ruie would predict. All 
search has hitherto failed to find any chemical system similar to that 
of oxygen and hemoglobin. 
It will probably occur to the reader that the adsorption of gases 
by indifferent solids, such as charcoal, is, at a given temperature, in 
proportion to the tension of the gas. In fact, it was suggested by 
Wolfgang Ostwald (1903) that the taking up of gases by hemoglobin 
is a case of adsorption. But weare met by nearly as many difficulties 
in this view as in that of chemical combination. The taking up of 
gases by charcoal follows the usual parabolic law, whereas that of 
oxygen by hemoglobin in solution in distilled water follows the 
rectangular hyperbola of a unimolecular reaction. On the other hand, 
the curve given by the latter system in the presence of electrolytes, 
acids or salts, requires a value greater than unity to be given to the 
exponent of the equation for the reaction velocity, in some cases above 
3, an exceptional value for the order of an equation for velocity of 
reaction. The curve approximates more to that for adsorption. 
The fact that there is a saturation point, beyond which increase 
of oxygen tension gives no measurable increase in the amount taken 
up by hemoglobin, is not in itself, of course, inconsistent with 
adsorption. But, again, it is a remarkable fact that the accurate 
determinations of Peters (1912) have shown that the amount of 
oxygen taken up in saturation is exactly that required to combine 
with the iron in the hemoglobin molecule to form FeO,; in other 
words, one molecule of hemoglobin combines with one molecule of 
oxygen. It is natural to associate the iron with the taking up of 
oxygen, but there is no other compound of iron having the proper- 
ties of hemoglobin. Even the hematin, which is combined with 
a protein to form hemoglobin, behaves in a way ‘similar to the 
dyes mentioned above. A further difficulty is the fact that hemo- 
globin takes up carbon dioxide, carbon monoxide and nitric oxide 
in a similar dissociable way to that in which oxygen is taken up, 
although in different amounts. Just as in adsorption, one of these 
gases drives out more or less completely another one. The absorption 
spectra of the CO and NO compounds is very like that of oxy- 
hemoglobin, although there is a difference between all of them and 
reduced hemoglobin. In any case it must be a remarkable chemical 
substance to combine with such dissimilar substances. According to 
Buckmaster and Gardner (1910-1911), chloroform is also taken up 
by hemoglobin, driving off part of the oxygen. 
In this connection, the relative adsorbing capacity of charcoal for 
various gases and vapours, the displacement of a weakly adsorbed 
