2230. Cement for Fixing Metal to Leather

2230.    Cement for Fixing Metal to Leather. Wash the metal in hot gelatine, steep the leather in hot gall-nut infusion, and unite while hot.

2231. Cement for Fixing Metal to Marble, Stone, or Wood

2231.      Cement for Fixing Metal to Marble, Stone, or Wood. Mix together 4 parts carpenters' glue and 1 part Venice turpentine.

2232. Cement for Coating Acid Troughs

2232. Cement for Coating Acid Troughs. Melt together 1 part pitch, 1 part resin, and 1 part plaster of Paris (perfectly dry.)

2233. To Cement Cloth to Polished Metal

2233.    To Cement Cloth to Polished Metal. Cloth can he cemented to polished iron shafts, by first giving them a coat of best white lead paint; this being dried hard, coat with best Russian glue, dissolved in water containing a little vinegar or acetic acid.

2234. Cement for Gas Retorts

2234.    Cement for Gas Retorts. A new cement, especially adapted to the retorts of gas-works, is very warmly recommended in a German gas-light journal. It consists of finely-powdered barytes and a soluble water-glass; or the barytes and a solution of borax. The joints are to be coated several times with this cement, by means of a brush. The addition of two-thirds of a part of clay improves the cement, and the retorts will then stand a red heat very well. Instead of the water-glass, a solution of borax may be used, or even finely powdered white glass.

2235. Use of Silicate of Potassa in Strengthening Fossil Skeletons

2235.    Use of Silicate of Potassa in Strengthening Fossil Skeletons. A very judicious application of the silicate of potassa (liquid glass) has been lately made at the Museum of Natural History of Paris, in repairing a great many fossil skeletons which had been disjointed and broken by the shells bursting in this Palace of Science. The solutions have been first used diluted to about 30° Baum'e, and afterwards of a higher degree of concentration. The adherence of the broken or separated pieces is brought together by applying with a brush some of the solution of the silicate of potassa on the parts to be joined, then they are left to dry, and the joint is hardly visible; and the joined part is far stronger than the remainder of the bone. Very delicate and porous anatomical pieces, as skeletons of birds, insects, etc., can be dipped repeatedly in more diluted solutions, and thus be rendered very hard and tenacious.

2236. Transparent Cement for Lenses, etc.

2236.  Transparent Cement for Lenses, etc.. It is frequently found necessary to cement together two surfaces of transparent glass, without destroying or injuring their transparency; this is especially the case in compound lenses. The best cement for effecting the union is Canada balsam, which, if too thick, should be thinned with a little turpentine, benzole, or ether. It is of importance that no air bubbles be present. In order to cement together the two parts of an achromatic lens (this consists of a double convex lens fitting exactly into the concavity of a plano-concave lens), having thoroughly cleaned the surfaces to be brought in contact, lay the glass, previously made warm, on a table suitably covered to prevent the. under surface from being scratched. By means of a peg of wood or otherwise, convey a drop of the balsam to the centre of the lens, and then gently lower down upon it the lens to be cemented to it, also previously made slightly warm. Now apply a slight pressure, and the dark disc in the centre, indicative of optical contact, will rapidly increase in size, until at last the balsam reaches the margin and begins to ooze out at the edges, if the balsam be present in excess, as it should be. By means of a piece of soft string passed crosswise over the lenses, tie the two together, and place them in a stove, an oven, or before a fire, for a short time, until the balsam at the edges shall have become hard and dry. Let the string then be removed and the lens freed from all external traces of balsam by means of benzole or ether. The above directions, modified to suit circumstances, apply to the cementation of transparencies or opal pictures ; also to the varnishing of magic lantern slides, and the protection of any transparent surfaces from the air.