513 
1898-99.] Sulphuric Acid and Sulphates in Solution. 
where the calculated percentage is below the observed, instead of 
above it as might be expected. 
On the whole, the agreement between the observed and calcu- 
lated values is fairly satisfactory. The mean real percentage 
difference between them is about 1 *5, and while the experimental 
error is probably less than this, it may in some cases amount to as 
much ; so that if we take this into consideration, and at the same 
time the fairly wide range of the experiments, the expression may 
be said to give at least a good approximation to the equilibrium 
actually existing in such solutions. 
From the percentages of free acid in the various solutions other 
interesting results may be obtained. The variation of this 
magnitude with the dilution, and with the ratio of acid to neutral 
sulphate is seen at once in the curves. 
The curve in fig. 1 shows the results of the first series of 
experiments, in which the concentration of the acid only was 
varied. If this curve is produced till it meets the origin of co- 
ordinates, it appears that the percentage of free acid rises at first 
very rapidly as the concentration of the sulphuric acid increases, 
and only when the amount of free acid in the solution has reached 
about 55 per cent, does the rise become somewhat slow. The 
continued curve also shows, for example, that in a 
100 solution 
of sulphuric acid, at least 50 per cent, of the acid still remains 
uncombined when as much as ten times the concentration of 
neutral sulphate is added to it. 
If the curve in fig. 2 is continued as shown by the dotted line, 
it meets the axis of y at the point 100, expressing the fact that 
when the concentration of the neutral salt is zero, the acid in 
solution is wholly free. 
In fig. 3 the percentages of free acid in solutions of the acid 
sulphate are plotted against the corresponding concentrations. 
It is evident that the amount of free acid in the solution increases 
with increasing dilution of the acid sulphate, a result which is in 
accordance with that of previous observers. If the curve is 
produced, it also meets the axis of y at the point 100, which 
simply means that the acid sulphate at infinite dilution is com- 
pletely decomposed into free acid and neutral sulphate. 
