nitrogen especially characterises animal, in contradistinction to vegetable, beings; nevertheless it is found in the latter, but in small quantities. The natural orders cruciferæ and fungaceæ are amongst vegetables especially rich in nitrogen. Inasmuch as animal beings contain so much nitrogen, and vegetables so little, Berzelius has imagined that nitrogen is generated in some unknown manner by the animal functions. This idea, however, has been opposed by Liebig, who, with the majority of chemists, believes that the nitrogen existing in plants is sufficient to account for the large quantities of that element locked up in the tissues of herbivorous, no less than other animals.

PREPARATION.-(1) By the combustion of phosphorus in atmospheric air; the result of which is the formation of phosphoric acid and the liberation of nitrogen.

DIAGRAMMATIC ILLUSTRATION OF THIS DECOMPOSITION.

Atmospheric air
Phosphorus

Nitrogen
Oxygen

A is evolved.

Phosphoric Acid.

(2) By transmitting chlorine through a solution of ammonia chlorine uniting with hydrogen to form hydrochloric acid, which combining with undecomposed ammonia, hydrochlorate of ammonia is formed, whilst nitrogen escapes.

(3) By agitating a liquid amalgam of lead and mercury with atmospheric air for two hours or more,― the result of which is absorption of oxygen and liberation of nitrogen.

(4) By mixing iron filings and sulphur with water, and exposing the mixture to atmospheric air for the space of forty-eight hours. In this, as in the preceding case, atmospheric oxygen is absorbed and nitrogen set free.

(5) By exposing muscle (flesh) to the action of nitric acid in a retort to which heat is applied. The theory of this decomposition is exceedingly complex, and cannot be satisfactorily explained.

PROPERTIES.-Nitrogen is permanently elastic and colourless. It has neither taste nor smell, does not act upon vegetable colours, nor does it whiten lime-water. By this latter characteristic especially it is distinguished from carbonic acid. It is neither acid, nor alkaline, neither supports combustion nor burns,—although its chemical relations impart to it some claim of being regarded a combustible. Water which has been boiled absorbs it to the extent of one and a half per cent. Its

refractive power is rather greater than that of atmospheric air (1.0340 to 1) and 100 cubic inches of it at mean temperature and pressure, weigh 30.16 grains; hence its specific gravity is 0.972, as may be thus

Or, seeing that the atomic weight of nitrogen is = 14, and its atomic size = hydrogen or, its specific gravity may be deduced by multiplying the specific gravity of hydrogen (0-0694) by the atomic weight of nitrogen (14).

LECTURE IV.

NITROGEN.

APPARATUS AND APPLIANCES EMPLOYED IN THE FOLLOWING

LECTURE.

Apparatus for the combustion of oxygen in a jar over water, so that oxygen may be separated from the air, and nitrogen left.

Nitrogen already collected and washed.

Nitric acid.

Tin foil.

Copper turnings.

Litmus paper.

Iodide of nitrogen.

Ammonia.

Evolution of ammonia, from sal-ammoniac and quick-lime.

Various bottles of ammoniacal gas.

Prussic acid.

Mixture of two volumes nitric oxide gas and five volumes hydrogen platinised asbestos, and tube.

THE element Nitrogen, which I purpose bringing before your notice this day, is one of exceeding interest, under whatever aspect viewed. Whether we have regard to the enormous amounts of this element which pervade nature, or the importance of the functions to which it is

made subservient, the curious chemical affections with which it is endowed, the number and various conditions of its numerous compounds, or the apparent paradox of the most violent combinations resulting from an element which, in its simple state, is characterised by a quality of inaction or passiveness:-all these are considerations which bespeak our interest, in an eminent degree, for nitrogen.

But I am proceeding in anticipation of my subject: you have not yet seen or had other physical manifestation of this element of which I speak,-element I still must call it, although nitrogen is endowed with many qualities which lead one almost to imagine that it is really a compound.

The usual method of obtaining a supply of nitrogen for the purpose of experiment, consists in extracting it from the atmospheric air; or, I should rather say, in extracting from the atmosphere-oxygen, the associate of nitrogen; thus leaving the nitrogen isolated or alone.

For this purpose we avail ourselves of the strong combustive powers of phosphorus; which, when ignited in a closed measure of atmospheric air, removes all the oxygen in the condition of phosphoric acid, and sets nitrogen free.