HAIR, small filaments issuing out of the pores of the skins of animals, and serving most of them as a tegument or covering. In lieu of hair, the nakedness of some animals is covered with feathers, wool, scales, &c. Hair is found on all parts of the human body, except the soles of the feet and the palms of the hands ; but it grows longest on the head, chin, breast, in the armpits, &c. It is known that every hair does properly and truly live, and re ceive nutriment to fill and distend it like the other parts; which they argue hence, that the roots do nqt turn grey in aged persons sooner than the extremities, but the whole changes colour at once, and the like is observed in boys, &c. which shows, that there is a direct communica tion, and that all the parts are affected alike. It may be observed, however, that, in propriety, the life and growth of hairs is of a different kind from that of thq derived therefrom, or reciprocated there with. It is rather of the nature of vege tation. They grow as plants do out of the earth; or, as some plants shoot from the parts of others, from which, though they draw their nourishment, yet each has, as it were, its several life, and a distinct eco nomy. They derive their food from some juices in the body, but not from the nu tritious juices ; whence they may live though the body be starved.
The hairs ordinarily appear round or cylindrical; but the microscope also dis• covers triangular or square ones, which diversity of figure arises from that of the pores, to which the hairs always accom modate themselves. Their length depends on the quantity of the proper humour to feed them, and their colour on the qua lity of that humour : whence, at different stages of life, the colour usually differs. Their extremities split into two or three branches, especially when kept dry, or suffered to grow too long; so that what appears only a single hair to the naked eye, seems a brush to the microscope.— The hair of a mouse, viewed by Mr. Der ham with a microscope, seemed to be one single transparent tube, with a pith made up of fibrous substances; running in dark lines, in some hairs transversely, in others spirally. The darker medullary parts or lines, he observes, were no other than small fibres convolved round, and lying closer together than in the other parts of the hair ; they run from the bottom to the top of the hair, and, he imagines, may serve to make a gentle evacuation of some humour out of the body : hence, the hair of hairy animals, this author sug gests, may not only serve as a fence against cold, &c. but as an organ of insen sible perspiration. Hair makes a very considerable article in tommerce, espe cially since the mode of perukes has ob tained. The hair of the growth of the northern countries, as England, &c. is va lued much beyond that of the more south ern ones, as Italy, Spain, the south parts of France, &c. The merit of good hair con sists in its being well fed, and neither too coarse nor too slender ; the bigness ren dering it less susceptible of the artificial curl, and disposing it rather to frizzle, and the smallness making its curl of too short duration. Its length should be about t*enty-five inches; the more it falls short of this, the less value it bears.
The scarceness of grey and white hair has put the dealers in that commodity up on the methods of reducing other colours to these. This is done by spreading the hair to bleach an the grass like linen, after first washing it out in a bleaching \cater : this ley, with the force of the sun and air, brings the hair to so perfect a whiteness, that the most experienced person may be deceived therein, there being scarce any way of detecting the artifice, but by boil ing and drying it, which leaves the hair of the colour of a dead walnut-tree leaf.
Hair, like wool, may be dyed of any co lour.
Hair, which does not curl or buckle na turally, is brought to it by art, by first boiling, and filed baking it, in the follow ing manner : after having picked and sorted the hair, and disposed it in parcels according to lengths, they roll them up, and tie them tight down upon little cylin drical instruments, either of wood or earthen ware, a quarter of an inch thick, and hollowed a little in the middle, call ed pipes ; in which state they are put in a pot over the fire, theie to boil for about two hours. When taken out, they let them dry; and when dried, they spread them on a sheet of brown paper, cover them with another, and thus send them to the pastry-cook, who making a crust or coffin around them, of common paste, sets them in an oven till the crust is about three-fourths baked. The end by which a hair grows to the head is called the head of the hair ; and the other, with which they begin to give the buckle, the point. Formerly, the peruke-makers made no difference between the ends, but curled and wove them by either indifferently ; but this made them unable to give a fine buckle, hair woven by the point Aker taking a right curl.
Hair is also used in various other arts and manufactures: in particular the hair of beavers, hares, conies, &c. is the prin cipal matter whereof hats are made. Spread on the ground, and left to putrefy on corn-lands, hair, ac all other animal substances, viz. horns, hoofs, blood, &c. proves good manure.
This, like every part of the animal sys tem, has been chemically analysed, and has been found to contain a large portion of gelatine, which may be separated from it by boiling. It then becomes brittle, the gelatine being the principal cause of its suppleness and toughness. From some experiments by Mr. Hatchett, it is infer red, that the hair which loses its curl in moist weather, and which is softest and most flexible, is that which yields its ge latine most readily ; whereas strong and elastic hair yields it with the greatest difficulty, and in the smallest proportion. By an experiment of Berthollet's 1,152 parts of hair'yielded The oil was soluble in alcohol, burnt with brilliancy, and with scintillations like the hair itself The coal was attracted by the magnet, which proves it contains iron. The alkalies, at a boiling heat, dis solve hair, and form with it an animal soap. Sulphuric acid dissolves hair, with the aid of heat. Hair is usually distin guished into various kinds : the stiffest and strongest is called bristles, such as that on the backs of swine. When re markably soft and pliable, it is denominat ed wool, as that on sheep ; and the finest of all is called down. From wool more than half its weight of oxalic acid is ob tained. Feathers possess similar proper ties to those of hair ; the quill is composed of coagulated albumen, but no gelatine. Muriatic acid dissolves hair, and the so lution is very like a solution of glue in the same acid. When plunged into acid, in the state of gas, it is very soon converted into a pulp.