78 Skene .— The Acidity of Sphagnum and its 
IV. The Variation of Acidity in different Sphagna. 
Paul pointed out that the different Sphagna exhibit different degrees 
of acidity. It seemed possible that the differences were secondary and not 
primary. Were all the species of the same initial acidity, then those which 
live in stations where the mineral supply is low would absorb less base than 
those in more favourable stations, would retain more unsatisfied acid, in 
other words they would appear to be more acid. 
I tested this theory by washing out the absorbed bases and deter¬ 
mining the acid in the washed material. 3 grm. of dry Sphagnum was 
shaken with 1 litre of distilled water saturated with carbon dioxide from 
a Sparklet bottle ; the water was changed thrice, and the washing lasted in 
all forty-eight hours. By this means about 90 per cent, of the absorbed 
base may be washed out. The residue was dried, and the acidity deter¬ 
mined in the usual way. A considerable number of species was investigated, 
and material of each was obtained from as many localities as possible. The 
results are set down in Table VI. 
The difference in acidity is primary; the washing out constantly 
increases the acidity, but almost no general levelling up between the 
different species takes place. On the whole they retain their relative 
positions, and probably the order would be still more nearly the same 
if a larger number of determinations were made, for the individual differ¬ 
ences are considerable. This goes to strengthen the conclusion of Paul, 
that those species which live in stations poor in food-stuffs require the 
highest acidities in order to obtain the necessary amount of bases. More¬ 
over, the amount of absorbed base, which is equivalent to the amount of 
the acid saturated, may be obtained by subtracting the secondary from the 
primary acidity. The results are given in the sixth column of the Table, 
and it is seen that the values for the various species lie quite close together. 
In particular the variations are scattered through the series ; there is no 
progressive increase in the amount of saturated acid with increase in 
acidity ; that is to say, the different species, by virtue of their different 
acidities, are able to hold approximately the same amount of base in reserve. 
In Paul’s Table the acidity seems, with one exception, to have been 
determined in a single sample. The differences between the species are 
small, frequently smaller than the differences between samples of one 
species as shown in my determinations. The samples of one species agree 
only moderately well; it is certainly impossible to get a value holding for 
all samples of a species, and it is scarcely permissible to take the acidity of 
a single sample as representative of the species as a whole. 
Further, Paul’s results were obtained by titration with sodium hydroxide. 
Rindell (Tl) has remarked on the impossibility of obtaining an exact end¬ 
point with this method ; I, too, found that in many cases the solutions 
