Elements of Chemical Philosophy
Humphry Davy, the celebrated natural philosopher, was born Dec. 17, 1778, at Penzance, England. At the age of seventeen he became an apothecary's apprentice, and at the age of nineteen assistant at Dr. Beddoes's pneumatic institution at Bristol. During researches at the pneumatic institution he discovered the physiological effects of "laughing gas," and made so considerable a reputation as a chemist that at the age of twenty-two he was appointed lecturer, and a year later professor, at the Royal Institution. For ten years, from 1803, he was engaged in agricultural researches, and in 1813 published his "Elements of Agricultural Chemistry." During the same decade he conducted important investigations into the nature of chemical combination, and succeeded in isolating the elements potassium, sodium, strontium, magnesium, and chlorine. In 1812 he was knighted, and married Mrs. Apreece, née Jane Kerr. In 1815 he investigated the nature of fire-damp and invented the Davy safety lamp. In 1818 he received a baronetcy, and two years later was elected President of the Royal Society. On May 29, 1829, he died at Geneva. Davy's "Elements of Chemical Philosophy," of which a summary is given here, was published in one volume in 1812, being the substance of lectures delivered before the Board of Agriculture.
I.—Forms and Changes of Matter
The forms and appearances of the beings and substances of the external world are almost infinitely various, and they are in a state of continued alteration. In general, matter is found in four forms, as (1) solids, (2) fluids, (3) gases, (4) ethereal substances.
1. Solids. Solids retain whatever mechanical form is given to them; their parts are separated with difficulty, and cannot readily be made to unite after separation. They may be either elastic or non-elastic, and differ in hardness, in colour, in opacity, in density, in weight, and, if crystalline, in crystalline form.
2. Fluids. Fluids, when in small masses, assume the spherical form; their parts possess freedom of motion; they differ in density and tenacity, in colour, and in opacity. They are usually regarded as incompressible; at least, a very great mechanical force is required to compress them.
3. Gases. Gases exist free in the atmosphere, but may be confined. Their parts are highly movable; they are compressible and expansible, and their volumes are inversely as the weight compressing them. All known gases are transparent, and present only two or three varieties of colour; they differ materially in density.
4. Ethereal Substances. Ethereal substances are known to us only in their states of motion when acting upon our organs of sense, or upon other matter, and are not susceptible of being confined. It cannot be doubted that there is such matter in motion in space. Ethereal matter differs either in its nature, or in its affections by motion, for it produces different effects; for instance, radiant heat, and different kinds of light.
All these forms of matter are under the influence of active forces, such as gravitation, cohesion, heat, chemical and electrical attraction, and these we must now consider.