EMERY WHEELS AND WHETSTONES.
Bolas thus describes their manufacture:
“When ordinary vulcanized rubber is heated to 230° Centigrade, (446° F.) or until it melts, a permanently viscous product is obtained, and this substance, if mixed with emery and sulphur to a kind of paste, forms a material out of which the so-called agglomerated emery wheels or grinders may be formed, the mixed materials being next hardened or cured by the application of a steam heat. Emery wheels and hones made on this principle were introduced by Deplanque about twenty-three years ago.
“Thirty-five parts of old vulcanized caoutchouc having been placed in a kind of still, heat is applied to melt it, the operation being assisted by the gradual addition of about ten parts of heavy coal oil; but this latter is afterward distilled off. The softened caoutchouc is then incorporated with 500 parts of emery of the required degree of fineness and nine parts of sulphur. These materials having been thoroughly mixed, the hones or wheels are manufactured, and afterward cured or baked at a heat of 140° Centigrade, (284° F.) during a period of about eight hours. Grinding wheels, made in the above manner, can be worked at a speed of 2,000 revolutions per minute, and are extremely useful for the working of hardened steel or other obdurate materials.”
Etching on Metals and Glass.—India rubber stamps can be used for placing the ground upon knife blades and similar articles which are to be etched. The parts untouched by the stamp are attacked by the acid. In the case of glass, diamond ink (page 133) can be put on with a stamp. The acids for metal etching might be thickened with barium sulphate also and applied in the same way. In these cases the inscription of the stamp would be etched. Where ground is put on, whether on glass or metal, the design for the stamp will be protected.
Etching Ground for Metals.—Equal parts of asphalt, Burgundy pitch and beeswax melted together and mixed thoroughly. It may be softened with mutton suet. Beeswax may be used, dissolved in ether or simply melted. Yellow soap is sufficient for ordinary work.
Etching Solutions for Biting in.—For steel and iron, a. sulphate of copper and common salt in solution. b. sulphate of copper, sulphate of alumina, and common salt, of each two drachms; acetic acid, 1½ oz. c. sulphuric acid, diluted with five volumes of water with a little sulphate of copper. For other metals, except gold and platinum, nitric acid diluted with five volumes of water.
Etching Ground for Glass.—Melted beeswax is generally recommended. It can be removed with spirits of turpentine after as much as possible has been scraped off.
Etching Glass.—Glass may be conveniently etched by exposing it to the vapor of hydrofluoric acid. A shallow leaden tray, as large as the glass, is required. A quantity of fluorspar is placed in it and is moistened with concentrated sulphuric acid. The glass is placed face downward over the tray. It is supported over the mixture by resting on the edges of the tray or by any simple method, and the whole is covered with a towel. In half an hour or more the etching will be completed. The vapors must not be allowed to escape into any room containing glass or metal articles as they corrode everything. Great care should be taken also not to let the mixture touch the hand, as painful ulcers are the result.
India Rubber Shoe Blacking.—Raw india rubber is given as a constituent of several shoe blackings. Formulæ are given as below for paste and liquid blackings.
I. Paste blacking: bone-black, 20 parts; molasses, 15 parts; vinegar, 4 parts; sulphuric acid, 4 parts; caoutchouc oil (as given below), 3 parts.
II. Liquid blacking: bone-black, 60 parts; molasses, 45 parts; gum arabic dissolved in water, 1 part; vinegar, 50 parts; sulphuric acid, 24 parts; caoutchouc oil, 9 parts.
Caoutchouc oil is made by dissolving or digesting virgin rubber 55 parts in linseed oil 450 parts.
Waterproof Composition for Boots.—One ounce of virgin rubber cut into pieces is digested in enough oil of turpentine to form a stiff paste. In applying heat take great care lest the contents of the vessel become ignited. When homogeneous, which condition may be brought about by rubbing in a porcelain mortar, as described in chapter XII., it is mixed with 5–6 ounces of boiled linseed oil. This gives an ointment almost of the consistency of butter.