Analyses of the Ashes of Plants. 
163 
I'lios. Aciil. 
1000 grains of white mustarcl-sccd digested in nitric 
acid, neutralised by carbonate of soda, and burnt, 
gave . . . . • '. . . . 18-04 
1000 grains perfectly oxidated by nitric acid, neu- 
tralised by carbonate of soda, and burnt, gave . 18 "25 
A review of these results, w e hope, will be considered to justify 
us in asserting that the ordinary methods of burning give per- 
fectly accurate results for phosphoric acid in non-silicious ashes ; 
incidentally they are satisfactory in proving the correctness of the 
methods employed in the analysis of the ashes when prepared, 
but of this we shall speak further on. We must, however, in 
this place slightly advert to the great doubt which the experi- 
ments described cast upon the opinion that phosphorus as such 
exists in the organic compounds of vegetables ; we know that 
phosphorus forms with hydrogen a compound similar in compo- 
sition and many of its characters to sulphuretted hydrogen. If 
in the burning of plants unoxidated sulphur escapes in variable 
proportions, why should not unoxidated phosphorus, supposing it 
to exist, be equally dissipated in the combustion? In point of 
fact, in all the experiments given above, however varied may have 
been the burning, the resulting phosphoric acid has been found 
identically the same. Burnt in the usual way, or in a highly 
oxidating medium, the results have, within the limits of errors of 
analysis, proved perfectly coincident. We cannot reconcile these 
lacts with any theory which would suppose phosphorus to be 
present in vegetable structures in the same unoxidated form as we 
find sulphur to hold in them. 
But we have yet to consider whether in silicious ashes any loss 
of phosphorus can occur. Rose has rather hinted at the possi- 
bility of this occurrence than asserted that it actually does take 
place ; he supposed that phosphoric acid may be separated from 
its basis by silica, robbed of its oxygen by charcoal, and volatilized 
as phosphorus. 
Reviewing the experiments just described, and calling to mind 
the tenacity with which phosphoric acid retains its last equivalent 
of base, and the very high temperature which is required for the 
reduction of the acid in the manufacture of phosphorus, a tem- 
perature which no careful analyst would dream of employing in 
the jireparation of plant-ashes — taking these points into consider- 
ation, we might anticipate with safety that the result of the 
investigation would in this case be also in favour of the ordinary 
methods of burning. "\Ve have, however, some more definite 
evidence to offer on this point. 
Barley, the ash of which contains about 30 per cent, of silica, 
M 2 
