Anahjses of the Ashes of Plants. 
155 
ash; it burned with ilifTiculty, ;vnd, the heat beings stronp:, there 
was a partial fusion towards the last, accompanied by the evo- 
lution of white fumes of sulphuric acid. The ash was dissolved 
in nitric acid, and the sulphuric acid precipitated by nitrate of 
barytes. The sulphate of barytes weighed 43*32 grains = 14-89 
grains sulphuric acid. 
Sulphuric acid in the sulphate of potash . . 20*85 
„ in the ash 14' 89 
„ driven off in the burning . . 5*96 
It is thus evident that there is liability, in the ordinary method 
of burning, to loss of sulphuric acid wherever silica is present 
in any quantitv, that is, in all silicious ashes. The temperature 
at which this occurred was higher than is at all admissible or 
necessary generally, but still the analyst could never feel sure 
that the temperature was so perfectly regulated that no loss of 
sulphuric acid had occurred in the usual way of burning. 
So far with regard to loss of sulphuric acid in the preparation 
of silicious ashes. 
It next became necessary to determine whether loss could be 
occasioned by other ingredients in the absence of a large per- 
centage of silica; and, as before, phosphoric acid and acid phos- 
phates were considered to be the only agents capable of vitiating 
the results in the burning of non-silicious vegetables. 
An experiment was made to ascertain if a phosphate containing 
two equivalents of fixed base (a pyrophosphate) was capable of 
decomposing a sulphate. For this purpose a mixture was made 
of pyrophosphate of soda and sulphate of potash, both previously 
strongly heated, in the following proportions : — 
Sulphate of potash . . . 47"86 
Pyrophosphate of soda , . 37 "74 
85-60 
These materials were perfectly mixed, and heated to redness in the 
air -flame of a gas-lamp for two hours, at the end of which time no 
loss of weight had occurred. The mixture was then introduced 
into a furnace and more strongly heated, till the materials w(>re 
fused into a limpid liquid. Upon cooling, the mixture was found 
to have undergone no change of weight. A second experiment 
gave similar results. A phosphate of two atoms of fixed base is 
therefore incapable of decomposing a sulphate or of causing loss 
of sulphuric acid in an ash. 
An experiment was next instituted to ascertain if a mono-basic 
phosphate would exercise any influence upon the sulphate of an 
