XVII. On the Action of Nitric Acid on various V sgetahles, with a more particular 
Examination of Spaitium scoparium, Linn., or Common Broom. 
By John Stenhouse, Esq., Ph.D., F.R.S. 
Received November 18, — Read December 12, 1850. 
The last paper which I had the honour of presenting to the Royal Society contained 
an account of the effects produced by the action of sulphuric and hydrochloric acids 
on the matiere incrustante of several plants belonging to the different great classes of 
vegetables. In the present paper I intend to describe the effects of nitric acid upon 
a variety of vegetable groups ; these researches having been undertaken in the hope 
that, by means of this powerful reagent, some light might perhaps be thrown on pe- 
culiarities in their respective constitutions. 
Populus halsamifera. 
The first plant experimented on with this view was the Populus halsamifera, as 
representing the numerous family of the Poplars. A quantity of the branches of this, 
in Great Britain, very common tree, was therefore cut into small pieces and was 
boiled with water till it was completely exhausted. The dark-coloured bitter-tasted 
liquid which it yielded was evaporated to the state of an extract. This extract was 
then digested with dilute nitric acid for about four and twenty hours. A great deal 
of nitrous fumes were given off, together with a small quantity of an agreeably smell- 
ing aromatic oil. The strongly acid solution was evaporated to dryness on the water- 
bath, so as to drive off as much of the adhering nitric acid as possible. The dried 
residue was next dissolved in a considerable quantity of hot water, and after being 
allowed to cool, was carefully filtered through a cloth. The clear liquid was then 
concentrated by cautious evaporation, and exactly saturated in the cold with carbonate 
of potash, great care being taken not to add an excess of the alkali. A yellow sedi- 
ment soon began to appear, and its amount was greatly increased in the course of a 
few hours. It consisted of nitropicrate of potash and of the potash salt of a new 
acid, to which I have given the name of nitropopulic acid. The mother-liquor con- 
tained a great deal of oxalate and nitrate of potash. The mixed precipitates were 
then collected on a filter and dried by pressure, so as to remove as much of the 
adhering mother-liquor as possible. They were then washed with a little cold water 
and were treated with a cold solution of dilute carbonate of potash, which readily 
dissolved out the nitropopulate of potash, while it left the nitropicrate of potash 
unacted on. The two salts were then separated by filtration, the nitropicrate of 
potash remaining on the filter, while the nitropopulate of potash was dissolved in the 
alkaline liquid. The mother-liquor was again slightly supersaturated with muriatic 
MDCCCLI. 3 H 
