12 THE EQUILIBRIUM OF COLLOID AND 



maintained by Wolfgang Ostwald that in the case of oxygen and 

 haemoglobin the phenomena is one of adsorption. Yet in the case 

 of oxygen and haemoglobin there exists at the point where absorp- 

 tion is complete an exact stochiometric relationship of one molecule 

 of oxygen to one molecule of haemoglobin, the molecular weight of 

 haemoglobin being fixed by the iron determinations which can be 

 carried out with great exactitude. Now the existence of exact 

 stochiometric relationships is usually supposed to be one of the 

 strongest criteria for chemical combination. Further, there is 

 the very definite and distinctive oxy-haemoglobin spectrum, quite 

 definitely different from that of " reduced haemoglobin," and the 

 fact that other gases, such as carbon-monoxide, replace oxygen 

 at saturation point in exactly equal volume to the oxygen required 

 to saturate. 



It would appear from this conflicting evidence that the form 

 of the pressure absorption curve as a criterion between adsorption 

 and chemical combination breaks down, rather than to be proved 

 that the uptake of oxygen by haemoglobin is adsorption and not 

 chemical combination. 



The other supposed criterion that there shall exist simple 

 stochiometric relationships at the saturation point between the 

 two substances uniting also breaks down in the case of unions 

 between colloids and crystalloids for several reasons. 



For the appearance of absence of stochiometric relationship 

 may be fallacious, and there may be such relationships quite de- 

 finitely and true chemical union where there is apparently absorp- 

 tion, because the total mass of the colloid may not be identical or 

 proportional to its active mass. For example, the crystalloid, such 

 as a dye, may not penetrate the aggregate of the colloid, and the 

 chemical reaction may occur on the surface of the colloid only ; 

 and since it is impossible to estimate the active mass lying on the 

 surface and participating in the reaction, exact relative molecular 

 masses may be involved and yet there be apparently no such 

 relationships. Conversely, there may be no true chemical union, 

 and yet the masses of the two substances bear quite definite mole- 

 cular relationships. For, if we consider, for example, the protein 

 molecule, with a given number of amidogen groups each chemically 

 saturated as to valency, and yet each possessing a certain residual 

 amount of basic affinity, and if now to this protein we add in 

 increasing quantity a substance with weak and chemically saturated 



