entering into the composition of animals and vegetables, chiefly in the form of water and ammonia.

PREPARATION.-Process I.-By the electrolysis of water, each resulting gas being separately collected. This process liberates hydrogen in the condition of absolute purity.

Process II.-By adding a mixture of one part oil of vitriol by measure, and about four or six by measure of water, to comminuted zinc or iron.

Theory of the Process.-Neither zinc nor iron are capable of uniting directly with sulphuric acid: oxide of zinc and of iron, however, combine readily. Thus, a decomposition of water is determined. Oxygen of

water uniting with zinc or iron, forms an oxide of these metals respectively, hydrogen being developed. In a diagrammatic representation the decomposition may be thus expressed :

Process III.-By transmitting aqueous vapour through a gun-barrel or other tube of iron heated to redness.

Theory of the Process.-The water being decomposed, its oxygen unites with the iron of the tube,-and hydrogen is evolved.

N.B.-By neither process-II. nor III.-can hydrogen gas be obtained in a complete state of purity, in either case being contaminated with a carbonaceous result. Perhaps, also, when zinc is used with a little of that metal in solution. The latter may, however, be separated by transmission through solution of potash.

Process IV.-By passing up into a tube inverted, and filled with water, a piece of potassium or sodium. Theory of the Process.-The potassium or sodium uniting with oxygen to form potash or soda, hydrogen is liberated.

PROPERTIES.-Permanently uncondensable and aëriform-neither taste nor smell when pure. Slightly soluble in water (108 cubic inches of water dissolve at 60° F. about 1.5 inches of the gas). May be respired once or twice with impunity, but if continued is fatal. Is a combustible, but does not support combustion. Is neither acid nor alkaline,—and the sole result of its combination with oxygen is water. The lightest ponderable body in nature, being sixteen times lighter than oxygen, and lighter than atmospheric air, in the ratio of 1 to 0.0696, which latter number is, therefore, said to be the specific gravity of hydrogen. At the temperature of 32°, 100 cubic inches of hydrogen weigh 2.22756 grains. Hydrogen is usually regarded as the unit of atomic weight, and the size of its combining volume is double that of oxygen.

LECTURE III.

HYDROGEN.

MATERIALS AND APPARATUS REQUIRED FOR ILLUSTRATING THE LECTURE.

Granulated zinc.

Sulphuric acid.

Water.

Taper adapted to copper wire.

Mixture of two volumes hydrogen and one oxygen in a jar standing on the pneumatic trough.

Bag and jet for blowing soap-bubbles with mixed gases.

Cavendish's eudiometer, electrical machine and Leyden jar.

Candle and oil lamp for demonstrating that water results from their combustion.

Voltaic battery and tubes for collecting oxygen and hydrogen from water decomposed.

Platinum wire to be ignited by the voltaic battery.

Apparatus for passing steam over red-hot iron and developing hydrogen.

Inverted tube filled with water, for the purpose of generating hydrogen by contact with sodium.

Spongy platinum.

Hydrogen and chlorine in tubes to be exposed to sun-light.
Bromine and hydrogen and hot wire.

Chlorine and hydrogen ready to be exploded in Cavendish's eudiometer.

Hydrochlorate of ammonia for the evolution of hydrochloric acid by contact with sulphuric acid.

Hydrochloric acid developed from salt-its properties to be investigated.

Hydriodic acid into an atmosphere of a little chlorine to show

iodine.

I CONSIDER it fortunate, in opening this lecture "On Hydrogen," that the arrangement of elementary bodies, as announced in the prospectus, enables me to take up hydrogen at the most convenient

period for bringing prominently before your notice, and by comparison with the elements already considered, some of its most remarkable points. You are aware that it is not my object in delivering this course of lectures to present you with the complete history of the relations of the non-metallic elements, but merely to illustrate certain leading points in connection with them.

I therefore shall say nothing concerning the history of hydrogen, but shall at once bring before your notice the methods of preparing this element.

Without going into details of manipulation and apparatus, let me at once proceed, in a simple way, to show how hydrogen may be produced.

It is ordinarily evolved by adding either zinc or iron to a mixture of oil of vitriol and water.

To illustrate this process I take the metal zinc, because not only is it nearest at hand, but because the result of its action, when brought into contact with the acid mixture, is that to which my table refers:

Putting, then, some of the metal zinc reduced to small granules into this glass flask, and adding to it a mixture of oil of vitriol and water, observe the powerful action which takes place. The liquid itself becomes disturbed as if it were boiling, and the gas escapes.

But how are you to have evidence of this escape, for there is no colour, as was the case when we were dealing with chlorine? I have an evidence of the development of hydrogen by the recognition of a peculiar smell; and if I apply a lighted taper to the mouth of the flask, then you observe a still further evidence the gas takes fire.

But for the purpose of still further learning the properties of hydrogen, it will be necessary to collect some, which can easily be done by means of the pneumatic trough.

[The lecturer proceeded to collect some hydrogen by the usual method, and a few words respecting the manipulation of which collection may not be out of place.

The granulation of zinc, of which mention has been made, is effected by pouring melted zinc in a small stream, and from an elevation of four or five feet, into a vessel of cold water. The granulation is only a convenient means of reducing zinc to the necessary degree of comminution; and, were it not for the loss of time involved by the operation of cutting, the latter process of comminution would serve as well.