Dandeno — Relation of Mass Action to Toxicity. 437 



Aet. XML — The Relation of Mass Action and Physical 

 Affinity to Toxicity, with incidental discussion as to hoiv 

 far electrolytic dissociation may he involved; by J. B. 

 Dandeno. 



Mass action, as a principle underlying chemical phenomena, 

 is comparatively well established. The law may be briefly 

 stated, that when any substance in a dissolved state enters into 

 a chemical reaction, the amount of the action is proportional to 

 the active mass of the substance. By mass of substance in solu- 

 tion, or molecular concentration, is meant the number — not 

 actual but relative — of molecules per unit of volume. It may be 

 expressed as so many gram-ions per liter of solution. An illus- 

 tration of mass action is here given. When potassium nitrate 

 and sulphuric acid are mixed in solution, a reaction, depending 

 upon the mass of each in solution, takes place. Thus, if the 

 acid be in excess, the resulting products are potassium bisul- 

 phate (KHS0 4 ) and nitric acid ; but if a large excess of nitric 

 acid be added to potassium bisulphate, the resulting products 

 are H 2 S0 4 and KJ^0 3 . Such phenomena, though common 

 enough in chemistry, are not well understood. 



In this paper an effort is made to set forth one point of view 

 from the physiological side. The radicles of some seedlings are 

 used as the physiological reagent, and a few common solutions 

 as the chemical ; and silica to represent a possible physical 

 agent. 



By physical affinity is here meant the force of attraction, 

 without chemical change, that substances may have for one 

 another in solution. As will be shown in some of the experi- 

 ments described in this paper, there is a very considerable 

 amount of such attraction. It has been pointed out* that, 

 with certain toxic solutions, the toxicity was much reduced 

 when non-chemical f substances were present. But just to 

 what extent such non-chemical substances have to do with the 

 well-being of plants, little is at present definitely known. 

 From this it is not to be inferred that such effects are the only 

 effects which may result from the presence of non-chemical 

 substances. It is this action alone, — this hindrance to the 

 chemical action (which would take place if the non-chemical 

 substance were not present) — which is here considered. 



The importance of this is at once apparent, when one consid- 

 ers that the great mass of soil particles are non-chemical in their 



* Dandeno, Trans. Can. Inst., vii, p. 315. 



f By non-cheniieal substances is here meant those substances which do not 

 react chemically in the experiment in question, and which are not soluble in 

 the liquid used. 



