Since we published the article on hair lotions, a few weeks since, we have received several letters from correspondents, thanking us for the information ; and in some of these, requests have been made for matter as reliable regarding hair dyes, which are generally sold at high prices. Hair can be dyed every color by the same processes and chemicals as thoseusedin coloring wool; but these are not applicable to hair on the living animal, as in almost every case, wool requires to be boiJed in hot liquors. It has been found that the salts of some metals are adapted to the coloring of hair in a cold state; and these have been, and are, applied to change grey and red hair into brown and black. As grey hair imparts the appearance of advanced age to persons who may have become prematurely so by sickness, or other causes, it is quite natural that such should have a pardonable desire to make the color of their hair correspond with their years. In oriental countries the practice of coloring the beard has existed from time immemorial; and some of the inhabitants of Persia exercise a queer fancy in the choice of color. With us, a black beard is the grand point of "bearded beauty," but in Persia, blue beards are quite common. These are colored with a preparation of indigo ; but it would be of no avail to describe how, as the boldest of the masculine gender among us dare not flourish one, well knowing that if he did so—from the low estimation in which he would be held by the fair sex—he would soon " die of the blues." All dyes only color to the root of the hair ; they must, therefore, be applied as often as the natural hair grows out and shows itself. The cheapest hair dyes are powders principally composed of lime and an oxyd of lead. The following is one of these :— Take two ounces of powdered litharge, half an ounce of calcined magnesia, and half an ounce of powdered slacked lime. They are mixed intimately together, and are ready to be applied by reducing tham to a cream-like consistency with soft water. When thus made into a paste, it is laid on the hair in a good coating, and then covered up with a silk handkerchief. The best time to apply it is before going to bed. In the morning it has to be rubbed off with a hard brush, for it sticks like mortar, and is a disagreeable, although an effectual dye. The hair is rendered harsh by it, and has to be softened with grease or oil. It is too troublesome for coloring the hair on the head, but may answer for dyeing the whiskers. This is the white powder sold for dyeing hair. Another recipe of the same kind is as follows :— Take one ounce of litharge, two ounces of carbonate or white lead, and three ounces of powdered quicklime. It is applied in the same manner as the former. Litharge and lime alone will also color the hair. The hair dyes principally composed of nitrate of silver are the most convenient and best. This salt of silver, when applied in solution to hair, and exposed to light, converts it either into a dark brown or black, according to the strength of the solution ; but it possesses the defect of staining the skin while it colors the hair ; this result, however, can be avoided if moderate care is exercised, as we shall describe:— Take twenty grains of gallic acid, and dissolve them in an ounce of water in an ounce vial; then take twenty grains of nitrate of silver, and dissolve them in half an ounce of soft water, to which should be added a weak solution of gum arabic or starch, and forty drops of ammonia, so as to fill an ounce vial. The gallic acid is now applied to the hair with a sponge, and allowed to dry ; the nitrate of silver solution is then applied in the same manner, and allowed to dry under exposure to bright light. In about ten minutes let the hair be washed, and it is found to be \ colored from grey to a dark brown. This is a good dye; and although it colors the finger-Snails and the hair, it scarcely stains the skin —the gum arabic and gallic acid preventing it from doing this. Considerable of the coloring matter is washed off loosely, but enough is taken up by the capillary tubes to dye the hair.' The ammonia may be omitted, and a weak solution of the hydro-sulphuret of ammonia used as a wash upon the top of the silver, after the latter has been on about five minutes. This is called the '" magic hair dye," because it is so rapid in its action. Either ammonia or hydro-sulphuret of ammonia is necessary to color grey hair black ; a strong solntion of galls or sumac may be substituted for the gallic acid. The sulphuret of potassium (in solution) may be substituted for the gallic acid, the ammonia and the sulphuret of ammonia, by applying it to the hair first, and then allowing it to dry before the silver solution is put on. It has a disagreeable odor, however; but this may be counteracted by a perfume, such as oil of bergamot, lavender, or rose water. In applying any nitrate of silver solution to the hair, some care should be exerci5ed to prevent it touching the skin. One ounce of the sugar of lead dissolved and mixed with six ounces of the sulphuret of alcohol, (alcohol in which flour of sulphur has been steeped,) darkens the color of the hair and restores it, in a measure, if grey, to its natural color. Some perfume must be added to this mixture—rose water is commonly used. This lotion is called "hair color restorer." It is miserable stuff, and ought never to be used. These hair dye specifics may be greatly increased in number without an increase of useful knowledge. We have given the best that are used, so far as we know. The nitrate of silver costs one dollar per ounce; the other ingredients are cheap. For a few cents a person may color his red or grey beard by the above methods a splendid black, rivaling that of the darkest crow.