90 "COEFFICIENT OF DIFFUSION OF CELLS" 



more acid than this, for we have never yet seen 

 any cell stain on a jelly which is acid beyond the 

 extent of 1 unit. We must remember all along, 

 however, that the jelly at the outset is acid to the 

 extent of 2 units, and then go ahead with alkali. If 

 we add to Solution No. 2 10 units of alkali, we say 

 that the jelly contains 10 units; but in reality it is 

 only alkaline to the extent of 8 units, for two of 

 them have been utilised in neutralising the original 

 2 units of acid. Of course, the neutralisation of 

 the acid increases the content of sodium citrate to 

 a slight extent, but it is so small that it can be 

 neglected. As a matter of fact, by saying that the 

 content of sodium citrate is usually 3 units, which is 

 in excess of the reality, we compensate for the extra 

 salt produced by neutralisation of the acid. The 

 neutral point we ignore. If a jelly contains only 

 2 units of alkali, it is in reality neutral; but w r e 

 need not trouble about that. There is no neutral 

 point in the equation, nor is there a symbol for acid; 

 yet the neutral point and acid both exist in the 

 equation, for the symbol "2a" means neutrality; 

 and the symbol "a" means 1 unit of acid, whereas 

 the absence of the symbol "a" means 2 units of acid. 

 To recapitulate: Acids and the neutral point are 

 omitted from the equation, but the jelly is acid at 

 the outset, and we deal only with alkali. If a jelly 

 contains only 2 units of alkali, that jelly is neutral. 

 If a jelly contains 15 units of alkali, it really is only 

 alkaline to the extent of 13 units. The jelly basis 

 with which we work is known as "coefficient jelly." 



