520 Proceedings of Royal Society of Edinburgh. [sess. 
The calculated values of the percentages of free acid given in 
the next table were obtained by means of this formula. The 
agreement between them and the observed values is fairly satis- 
factory, as may be seen in the curves in fig. 5. The general 
aspect of the two sets of numbers is, on the whole, the same as 
in the preceding cases, the mean difference between them being 
somewhat over 1 
per cent. 
Percentage Free Acid. 
h 2 so 4 
Li 2 S0 4 
(Observed.) 
(Calculated.) 
0*025 
+ o-i 
62*2 
63-9 
0-05 
5) 
68-4 
68-5 
0-1 
JJ 
73-6 
74-0 
0-2 
33 
81-9 
80'2 
0-35 
33 
86-3 
85*3 
Fig. 5. 
Equilibrium in Solution between Sulphuric Acid, the Neutral 
and the Acid Sulphates op the Alkali Metals. 
It may be said, then, as the result of all the experiments and 
the deductions from them, that the equilibrium between sulphuric 
acid, the neutral and the acid sulphates of potassium, sodium, and 
