(a) In making a cement one should know pretty thoroughly what is to be expected of it before they could advise upon it. For instance, an ordinary rubber cement will hold on a host of different surfaces and with the best 5 of success, except where there is continued dampness. For holding to damp walls, or surfaces where there is a constant pressure of moisture there is nothing equal to Jeffrey's marine glue, the formula for which has been published and republished all over the world. It consists of - 1 part rubber, 12 parts coal tar, and 2 parts asphal-tum. The rubber, after having been massed, is dissolved in the undistilled coal tar, and the asphaltum is then added. This glue, as its name indicates, is oftentimes used for mending articles at sea, or patches, for instance, that are to be laid on surfaces that are to be under water, and it has been found to be a most excellent thing.

(6) Of glass cements there are a great many, rubber as a rule being dissolved in some very vo!atile solvent and some hard drying gum is added.

(c) A guttapercha cement for leather is obtained by mixing the following. It is used hot. Guttapercha, 100 parts; black pitch or asphaltum, 100 parts; oil of turpentine, 15 parts.

(d) An elastic guttapercha cement especially useful for attaching the soles of boots and shoes, as on account of its great elasticity it is not liable to break or crack when bent. To make it adhere tightly, the surface of the leather is slightly roughened. It is prepared by dissolving 10 parts guttapercha in 100 of benzine. The clear solution from this is then poured into another bottle containing 100 parts linseed oil varnish and well shaken together.

(e) Good rubber cement for sheet rubber, or for attaching rubber, material of any description or shape to metal, may be made by softening and dissolving shellac in 10 times its weight of water of ammonia. A transparent mass is thus obtained, which, after keeping 3 or 4 weeks, becomes liquid, and may be used without requiring heat. When applied, it will be found to soften the rubber; but when the ammonia has evaporated, it forms a kind of hard coat, and causes it to become impervious to gases as well as liquids.

(f) Davy's universal cement is made by melting 4 parts common pitch with 4 of guttapercha in an iron vessel, and mixing well. It must be kept fluid, under water, or in a dry, hard state.

(g) A very adhesive cement, especially a lapted for leather driving belts, is made by taking bisulphide of carbon 10 parts, oil of turpentine 1 part, and dissolving in this sufficient guttapercha to form a paste. The manner of using this cement is to remove any grease that may be present on the leather by placing on the leather a piece of rag and then rubbing it over with a hot iron. The rag thus absorbs the grease, and the two pieces are then roughened and the cement lightly spread on. The two pieces are then joined, and subjected till dry to a slight pressure.

(A) A solution of guttapercha for shoemakers is made by taking pieces of waste guttapercha, first prepared by soaking in boiling water till soft. It is then cut into small pieces, placed in a vessel, covered with coal tar oil, tightly corked to prevent evaporation, and allowed to stand for 24 hours. It is next melted by standing in hot water till perfectly fluid, and well stirred. Before using it must be warmed as before, by standing in hot water.

(i) A cement for uniting rubber is composed as follows: 100 parts finely chopped rubber, 15 of resin, 10 of shellac; these are dissolved in bisulphide of carbon.

(f) Another rubber cement is made of 15 gr. rubber, 2 oz. chloroform, 4 dr. mastic; first mix the rubber and chloroform together, and when dissolved the mastic is added in powder. It is then allowed to stand by for a week or two before using.

(A) Cement for sticking on leather patches and for attaching rubber soles to boots and shoes is prepared from virgin or native rubber, by cutting it into small pieces or shredding it up; a bottle is filled with this to about 1-10th of its capacity; benzine is then poured on till about 3/4 full, but be certain that the benzine is free from oil. It is then kept till thoroughly dissolved, and of a thick consistency. If it turns out too thick or thin, suitable quantities must be added of either material to make as required.

(l) An elastic cement is made by mixing together and allowing to dissolve the following: 4 oz. bisulphide of carbon, 1 oz. fine rubber, 2 dr. isinglass, 1/2 oz. guttapercha. This cement is usea for cementing leather and rubber, and when to be used the leather is roughened and a thin coat of the cement is applied. It is allowed to completely dry, when the two surfaces to be joined are warmed and then placed together and allowed to dry.

(m) Cement used for repairing holes in rubber boots and shoes is made of the following solution: (1) Caoutchouc 10 parts, chloroform 280 parts. This is simply prepared by allowing the caoutchouc to dissolve in the chloroform. (2) Caoutchouc 10 parts, resin 4 parts, gum turpentine 40 parts. Fcr this solution the caoutchouc is shaved into small pieces and melted up with the resin, the turpentine is then added, and all is then dissolved in the oil of turpentine. The two solutions are then mixed together. To repair the shoe with this cement, first wash the hole over with it, then a piece of linen dipped in it is placed over it; as soon as the linen adheres to the sole, the cement is applied as thickly as required. (Chem. Trade Jl.)

Stone

(3). The following metallic cement for repairing broken stone was, according to Professor Brune, of the School of Fine Arts, used in the restoration of the colonnade of the Louvre, of the Pont Neuf, and of the Conservatoire des Arts et Metiers. It consists of a powder and a liquid. The powder: - 2 parts by weight of oxide of zinc, 2 of crushed grit, the whole intimately mixed and ground. Ochre in suitable proportions is added as a colouring matter. The liquid: - A saturated solution of zinc in commercial hydrochloric acid, to which is added a quantity by weight, of hydrochlorate of ammonia equal to one-sixth that of the dissolved zinc. This liquid is diluted With two-thirds of its bulk of water To use the cement, 1 lb. of the powder is to be mixed with 2} pints of the liquid. The cement hardens very quickly and is very strong.