A simple apparatus for creasing thin cardboard or heavy paper in a perfectly straight line without broken edges is described in the French magazine La Nature as follows: On a base of convenient dimensions are fastened two pieces of wood, well smoothed and of equal thickness, so that there remains a slot, about ¹⁄₈ in. wide, between them. At one end a hole is bored through these pieces for a shaft on which the creaser will turn. The creaser is made of a piece of wood somewhat longer than the baseboard so that a handle can be formed at one end. At the other end it is slotted for a piece of metal, perforated for the shaft and fastened with two pins or rivets, as shown. On the under side of the creaser a stiff steel wire is fastened so that it coincides with the slot. The wire is fastened by heating the ends red hot, bending them at right angles to the main part and driving them into the creaser.

A razorlike edge can be put on a knife blade by carefully stropping it without lubricant on a piece of smooth aluminum after first whetting on an oilstone.

A Miniature Illuminating-Gas Plant
By MORTON SOUTHARD

ery few persons realize that the smoke issuing from chimneys is mainly coal gas carrying minute particles of unconsumed carbon that gives it a dark-gray color, containing, besides, some sulphur and sulphuric gases, carbonic-acid gas, and other impurities. It is only necessary to collect the impurities to get a gas that will burn with a bright flame.

The products obtained from a gas plant are gas, ammoniacal liquor, coal tar, and coke. Of 1 ton of coal, 1,500 lb. remains in the retort, or furnace, as coke; 20 gal. of ammoniacal liquor and 140 lb. of coal tar are taken from the cylinders and washers. When distilled, the ammoniacal liquor will yield close to 18 gal. of ammonia, which is used in the manufacture of artificial ice and cold storage. The coal tar will yield approximately 19 lb. of benzol, which is the base of all true aniline dyes; 6 lb. of naphthalene, commonly known as camphor flakes or moth balls, which also yields some dyes; 4 lb. of toluene, which is valuable as a solvent and is the base of saccharine, and about 2 lb. each of phenol (carbolic acid), pyrene, anthracene, xylenol, cresol, chrysene, and alizarin. The residuum is coal-tar pitch, used extensively as a binder for briquetting coal dust for household consumption, and also for roofing and street paving. From these various coal-tar products, dyes of every tint, shade and color are obtained, as well as other industrial chemicals, from flavoring extracts to perfumes, from volatile oils to high explosives, and from the sweetest of all sweets to the bitterest of bitter.

A model gas plant—one that will be instructive and in no way dangerous if proper precautions are taken—can be built from a few fire brick, some pieces of pipe, and a few tin cans. Enough fire brick must be secured to build a furnace 14 in. square by 20 in. high, inside measurements. Build up the four walls on a level surface of the ground, laying the bricks with a cement mortar to seal them perfectly, as coal gas will find any small crevice and escape. For this reason it is best to build a second wall outside of the first and plaster the joint between them as it is built. When the four walls are finished, make a grate of fire brick in the bottom by setting the brick on edge and spacing them about ¹⁄₄ in. After the walls are dry, make ready the material for the fire. Place sufficient kindling on the grate to start a quick fire, then cover it with coal. When this is done, cover the furnace with a heavy piece of asbestos board large enough to reach the outside edge of the furnace walls. The board must be cemented to the top surface of the brick walls. Place the cement mixture on the wall top, then press the board on it, and place a weight on top until the cement becomes dry. The cement mixture should consist of one part cement to two parts of fine sand.

Procure a large can, such as used in canning tomatoes, having a diameter of more than 4 in. and with top and bottom whole; also two other cans, each having a capacity of 2 gal. with closed heads. Connect the first can to the furnace with a piece of 2-in. pipe, as shown in the illustration. The pipe can be bent for convenience, but in case such a piece is not at hand, regular pipe connections can be made with threaded ends, ells, waste nuts, etc. In either case, be sure to make the joints gas-tight. If a bent pipe is used, the ends can be cemented in the asbestos furnace top and the can top. Cut a hole centrally in the asbestos top and at one side in the can top. Fit one end of the pipe in the hole made in the asbestos and seal the connection with asbestos cement, then do likewise with the end that enters the can top.