158 
Analyses of the Ashes of Plants. 
following experiments on white peas afford evidence of a similar 
nature : — 
1000 grains of white peas hurnt in the usual way 
gave ..... 3 "357 sulph. acid. 
1000 grains dissolved in nitric acid and then 
burnt gave . . . . .3-611 „ 
A second experiment by the same method . 2 • 533 „ 
We have mentioned that in these experiments the oxidation by 
nitric acid was not complete. The following experiments show 
that even when no further action is produced by nitric acid the 
burning of the product is attended with the loss of sulphuric 
acid : — 
One thousand grains of white peas were perfectly oxidated by 
nitric acid, the action being continued till all the organic matter 
was destroyed. It is found that, as the evaporation proceeds, the 
product of this action suddenly takes fire, even although the 
])rocess is very slowly conducted. The 1000 peas, perfectly 
oxidated by nitric acid and burnt, gave 4* 182 of sulphuric acid ; 
a second experiment gave 4*962 of sulphuric acid. Here it will 
be seen that the perfect oxidation of the whole vegetable sub- 
stance by nitric acid does not prevent loss of sulphur in the sub- 
sequent burning. It is true that in both these latter experiments 
the proportion of sulphuric acid in the ash is greatly increased, 
but the results obtained are not uniform. Such a result was cer- 
tainly in some measure to be anticipated ; for, suj)posing that by 
the oxidation of the sulphur a large amount of sulphuric acid is 
produced, there is no provision for the union of this acid with 
the necessary proportion of fixed base in the ash, and it is conse- 
quently dissipated in the burning. 
The obvious remedy for this defect is to neutralise the acid 
liquids with an alkaline carbonate previous to burning, and this 
plan we, for several reasons, prefer to burning the vegetable sub- 
stance directly with a nitrate or chlorate. 
The plant is digested with strong nitric acid, by which it is 
rapidly attacked. When the substance of it has been broken 
down into a uniform pulp, the liee acid is neutralised by pure 
carbonate of soda. The mixture is evaporated and carefully 
burnt. 
The ash is then introduced into a deep flask, and treated very 
gradually by strong nitric acid till it becomes acid. It is import- 
ant to employ strong nitric acid and a deep rather than an open 
vessel ; because without these precautions there is a very con- 
siderable liability to loss, sulphuretted hydrogen being evolved 
from the alkaline sulphurets produced in the last stages of the 
burning. In the manner indicated there is, however, no loss; of 
