150 Prof. B. Moore. On Pree Hydrochloric Acid | Feb. 28, 
hydrochloric acid on the probable changes in the blood giving rise to this 
condition. 
It is clear that to obtain an estimate of the effective acidity or alkalinity of such 
solutions as occur in the body, we must make use of methods which do not 
disturb the equilibrium in the solution, and give us a measure from some activity 
of the hydrogen or hydroxyl ions. Such methods have already been elaborated in 
physical chemistry, and, at the suggestion of Ostwald, were first applied to estima- 
tion of the degree of acidity of the stomach contents by F. A. Hoffmann.* 
The methods depend upon the fact that the velocity with which an acid solution 
hydrolyses a substance capable of hydrolysis, such as cane-sugar or methyl-acetate, 
is proportional to the concentration of the hydrogen ions in the solution. 
For example, if cane-sugar solutions of equal strength be subjected to attack by 
equi-molecular solutions, on the one hand, say, of hydrochloric acid, and, on the 
other, of an organic acid, such as acetic. On account of the high state of 
ionisation of the hydrochloric acid, the cane-sugar is rapidly hydrolysed into invert 
sugar, and the rate of change can be accurately followed by the polarimeter, while, 
in the case of the acetic acid, which is but feebly ionised, the change is exceedingly 
slow. In fact, the change in the latter case is negligible compared with the 
former. 
The application of the method with cane-sugar solutions and the polarimeter is, 
however, cumbrous, laborious, and slow, requiring a polarimeter, accurate readings, 
and the use of controls, since the gastric contents themselves rotate the plane of 
polarisation. Hence, the more recent method used by Hoffmann, which is an 
application of Ostwald’s method of the catalysis of methyl-acetate, is much to be 
preferred, since it is much easier of application, can be applied in any laboratory 
where there is a thermostat or incubator, and facilities for volumetric analysis, and 
yields quite as accurate results as the other. The principle of the method is that 
methyl-acetate in aqueous solution changes with extreme slowness into methyl 
alcohol and acetic acid, according to the equation 
CH;.COO.CH; + H,0 = CH3.COOH + CH3.0H, — 
that this change can be increased enormously in velocity by the presence of an 
acid, and that the velocity is proportional to the concentration of the hydrogen 
ion of the acid, and the concentration of the methyl-acetate at any given moment. 
The amount of acetic acid formed in a given time when acids of different 
concentration act upon the same concentration of methyl-acetate, gives, at once, 
an indication of the relative degrees of concentration of the hydrogen ions of 
the acids, or a simple calculation gives from this figure the effective concentration 
of the acid in hydrogen ions. 
The determinations have been carried out by us as follows:—Ten c.c. of the 
gastric contents are taken in a small corked Erlenmeyer flask, 0°5 c.c. of the 
methyl acetate is added, and 5 c¢.c. of the mixture is titrated at once with deci- 
normal alkali, free from carbonate, using phenol-phthaléin as indicator. 
* *Centralblatt f. klin. Medicin,’ vol. 10, 1889, p. 793; ‘Verhand. Gd. Internat. med. 
Congresses,’ 1890, Abth. V, Abstract in Maly’s ‘ Jahresber.,’ vol. 21, 1892, p. 219. 
