Analyses of f lic Ashes of Phntfs. 
157 
It is plain, therefore, that with all possible attention to the burn- 
ing of vegetable substances, the quantity of sulphuric acid in the 
ash is anything but constant in different burnings of the same non- 
silicious plant. It was thought that the rapidity or otherwise 
with which the first part of the combustion was conducted would, 
in all probability, very materially affect the results. 
One thousand grains of the turnip-seed were perfectly dried 
and suddenly introduced into the platinum basin already red-hot : 
it caught fire immediMely and burnt witli much flame ; the burn- 
ing was continued as usual, and the ash analysed : it gave 2*260 
of sulphuric acid. 
One thousand grains were thoroughly dried and subsequently 
very gradually charred by immersion of the platinum dish in hot 
sand ; it did not catch fire at all. The charred mass was carefully 
and slowly burnt to ash; it gave 4' 680 of sulphuric acid. An- 
other experiment, precisely similar in conduct, gave 5- 700. 
It would seem, then, that great rapidity of burning dissipates 
more sulphur, whilst a careful avoidance of inflaming the plants 
gives the highest proportion of sulphuric acid in the ash. 
But at the same time it will at once be manifest that even this 
modification of the process of burning, although it retains the 
most sulphur, gives results anything but uniform or correct; and 
we convinced ourselves of the fact that sulphur passes off from a 
burning animal or vegetable substance in combination with hydro- 
gen. This evolution of sulphuretted hydrogen takes place at the 
lowest temperatures at which it is possible to burn organic sub- 
stances, and the escape of the gas can be made readily evident by 
suspending a piece of lead-paper over turnip-seed charred at a 
dull heat. Conceiving it certain that the sulphur which is dissi- 
pated in the burning of plants passes off in the state of sul- 
phuretted hydrogen, we were induced to try whether its oxidation 
previous to burning would not give more satisfactory results, and 
no better oxidating medium occurred to us than nitric acid, which 
was accordingly employed. 
One thousand grains of turnip-seed were digested in strono- 
nitric acid, aided by a gentle temperature. The action soon be- 
comes violent, with evolution of abundant fumes of peroxide of 
nitrogen. After the action had continued some time, but before 
the further addition of acid had ceased to produce any effect, the 
materials were turned out of the flask into the platmum dish, 
gently evaporated to dryness, and subsequently burnt. 
The thousand grains of turnip-seed, dissolved in nitric acid 
and burnt, gave 3-214 sulphuric acid. 
Tills quantity is inferior to that obtained in several experiments 
l)efore mentioned, where nitric acid was not employed. The 
method is therefore not attended with any advantage, The 
