148 Prof. B. Moore. On Free Hydrochloric Acid |¥Feb. 28, 
The + and — signs indicate the ionic condition, and the fact that in electrolytic 
conduction the property of carrying the current lies in the ionised portions. 
Similarly, many other properties are due to the ionised condition, and amongst 
other, the acid and alkaline properties. 
Now, for equilibrium in solution, a definite ratio must exist between m and n, 
which is dependent upon the nature of the acid or alkali and the concentration of 
the solution, and it is the variation of this ratio which is of interest to us here, 
and gives an experimental basis for determining the effective amount of acid or 
alkali in a given solution, which is not given by titration. 
For example, hydrochloric acid in the neighbourhood of such concentrations as 
are found in the gastric contents is over 95 per cent. dissociated into its ions and is 
correspondingly effective as an acid, while acetic acid in similar concentration is 
only dissociated to the extent of about 3 per cent.* and is correspondingly 
weakened in its activity as an acid, and the same is true of all the other organic 
acids occasionally present in the gastric contents. 
The same differences occur in the solutions of strong and weak alkalis, thus it 
was shown by Shieldst that for dilute solutions of caustic soda and sodium 
carbonate of equi-molecular strength that the effective strength, or hydroxyl con- 
centration, in the latter was only about 3 per cent. of the former. Such figures, as 
we shall see later, are of the utmost importance when we come to consider the 
relationship of the results we have obtained regarding the effective acidity of the 
gastric secretion to the effective alkalinity or acidity of the blood. 
The blood owes its reaction to indicators (such as phenol-phthaléin, litmus, etc.) 
to such substances as sodium carbonate in presence of excess of carbonic acid, and 
to phosphates of the alkalies containing varying amounts of base and acid. 
In such solutions the amount of effective acid (H ion) or alkali (HO ion) concen- 
tration is very low, and accordingly dependent upon the indicator used, the blood 
(and other fluids of the body, the various secretions, urine, milk, etc.) possesses an 
alkaline reaction (for example, to litmus or di-methyl) or an acid reaction (for 
example, to phenol-phthaléin). That is to say, in the case of the blood and many 
other fluids of the body there is both acidity and alkalinity according to the 
indicator used, for both acid ions and alkali ions are present, and the result obtained 
on testing will be dependent upon how the particular indicator is affected by these 
ions in the concentration in which they happen to be present. 
In an analogous fashion to the different indicators, the different cells of the 
secreting and excreting glands of the body will separate from the same solution, 
the blood plasma, which bathes them, the ions for which they possess a greater 
permeability or greater affinity, and furnish secretions or excretions of varying 
reaction and degree of reaction, that is to say, of varying concentration in hydrogen 
and hydroxy] ions. 
The varying reactions given with different indicators in the same fluid, looked at 
from the proper point of view, instead of being a source of confusion, hence serves 
* See Ostwald, ‘ Lehrbuch d. allgem. Chemie,’ 2te Auflage, vol. 2, p. 729. 
t ‘Zeitsch. f. Physik. Chemie,’ vol. 12, 1893, p. 167. 
