45 per cent. of fine quartz sand containing some ferric oxide and lime (so-called silver sand), 36 per cent. of minium, 11 per cent. of soda, 2 per cent. of saltpetre, 3.25 per cent. of pyrolusite, 2.5 per cent. of cupric oxide, and 0.25 per cent. of crystallized bismuth nitrate.

Mix the ingredients thoroughly and, after melting in a clay crucible, stir the melted mass and keep it in flux for some time. The resulting product when cold is a nearly black transparent glass, which can be easily shaped into pin-heads and fastened to steel pins by melting in the blast lamp. The heads show at first the dark appearance of the glass, but by bringing the melted glass mass, when no longer at a red heat, into the interior of the blast flame, it acquires in a few seconds the appearance and lustre of polished

Manufacture of Plate Glass. The following is one of the formulæ generally employed: Silica 78 parts, potash 2, soda 13, lime 5, alumina 2. The materials in a comminuted form are fused in crucibles or pots, exposed to an intense heat in a furnace, complete fusion requiring about 20 hours. From the pots it is ladled into a cistern, called the cuvette, which is also placed in a hot furnace, where it remains until the glass is fired and in proper condition to flow readily and equably. When this is the case the cuvette is lifted out of the furnace by means of tongs and hoisted on to a carriage by which it is moved to the casting table. It is then skimmed to remove impurities from its surface, and hoisted by a crane immediately over the casting table. The casting table is surrounded by side and end ledges corresponding in depth to the thickness of the plate to be made, to prevent the escape of the liquefied glass which is poured upon it by tilting the cuvette. During the pouring a washer is drawn immediately in front of the glass to remove any dirt from the casting slab, and when this has been covered to the requisite depth a heavy copper roller is drawn over the surface of the glass, causing it to exhibit a beautiful iridescent play of colors; this roller flattens its upper surface and causes an excess of the metal to be thrown off at the end of the table, where it is received in a trough of water.

A thick flange of the glass is turned up at the end of the plate, to which, when somewhat hardened, a rakeshaped iron is applied, by which it is forced into the annealing oven, or upon a carriage by which it is conveyed to the oven. As the plate is yet plastic, its under side takes an impression from the bricks of the oven, while the upper surface, though smooth, is uneven; it consequently requires to be ground and polished. After remaining in the oven about 5 days, and being allowed to cool gradually, it is carefully examined to see if it will admit of being finished as a single plate, or whether it has flaws or knots which necessitate it being cut into smaller pieces. If the latter be the case the defective portions are cut out and the remainder serves for plates of less size. In either

case the plates are embedded in plasterof-Paris upon stone tables about 8 feet wide and 15 feet long. The tables are arranged in pairs at about 10 feet distance apart.

Other plates of glass are cemented to the under surfaces of the two swingtables or runners, which by means of a horizontal frame between each are caused to traverse backward and forward, a circular motion being at the same time imparted by means of a vertical crank shaft pivoted to the central and upper part of the table and actuated by bevel-gearing; four other cranks, one at each corner of the frame, serve to guide and limit its motion, causing its central point to describe a circle about 4 feet in diameter, so that different portions of the faces of the upper and lower glass plates are continually applied to each other. Sharp river-sand sifted into two different sizes is used as an abradant; when the surface of the lower plate has been ground quite flat by the coarser sand, it is removed by careful washing, and the finer sand substituted for it: to this succeeds emery powder, a coarser and then a finer quality being applied, the glass being thoroughly washed previous to each change of material, so that none of the coarser particles previously used may remain to cause scratches on its surface. The plates are then inverted and the same process is repeated on the other side. For this purpose the frame above described is suspended by chains, which admit of its being raised from the surface of the lower table. These machines do not permit the use of very fine emery, as their weight and velocity at such near proximity as they would necessarily be would tear the surface of the glass; the velocity is consequently reduced when the finer emery is employed, and a different machine worked by hand-power is used for the final smoothing, preparatory to the process of polishing. This is effected upon stone benches about 2 feet high, having plane upper surfaces which are covered with wet canvas. Upon this one of the larger plates is laid, the wetted surface of the canvas serving to retain it in its place. A smaller plate is used as a grinder or runner; if this be of such size that a

uniform pressure of it cannot be imparted to it by hand, leaden weights are distributed over its surface. Emery powders of gradually increasing fineness are applied with water, and the runner is traversed back and forth by hand with a semicircular stroke, its path being slightly changed at each stroke, while the runner itself is gradually turned around as on an axis during the progress of the work. These combined movements serve to evenly distribute the emery, and insure an equal amount of grinding, both to the bed-plate and runner.

About six sizes of carefully washed emery are used in smoothing, and between each change the plates and everything about the apparatus are carefully washed, including the hands of the operators. The fine emery powder last employed imparts a very smooth surface to the plates, which are now ready for polishing. The polishing machine has a bed mounted upon rollers, and traversed slowly back and forth sideways by a rack and pinion beneath. Two carriages supported on wheels on each end, which run on rails at each end of the table, have a reciprocation of about 2 feet by means of two opposed cranks, so that one advances while the other recedes. They are placed about 4 feet apart, and to their under surfaces are attached rubbers having sockets in their upper parts into which bars with rounded ends on the under side of the carriage are fitted, allowing a certain freedom of motion independent of each other; they measure 6 x 8 inches, are placed at distances of 1 foot apart, and their faces are covered with thick felt. By the reciprocating motion of the carriage and the transverse movement of the bed they are caused to act on every part of the surface of the glass, a sufficient pressure being imparted to each by weights.

The powder generally employed in polishing is "Venetian pink," a substance containing a small proportion of oxide of iron mingled with earthy matter. It is used with water, which reduces the friction and prevents the glass from becoming heated. Tripoli, crocus, and putty powders, when used with water, cut too actively to produce. a high polish in this way; though

they are employed dry for the last finish in hand-polishing, the amount of surface acted on, with the velocity and power of the machinery, would render these liable to tear the surface of the glass, besides exposing it to the contingency of being broken by the heat evolved.

Ornamenting Frosted Glass. A method of ornamenting frosted glass for those who cannot draw is to choose some pretty pattern of lace curtains, lay it smoothly on thin paper, and with a pencil trace the outlines. Then, after making as many layers as you require patterns, cut out the designs at one time through the several layers of the paper with a pair of sharp-pointed scissors. Fasten the patterns with tacks to the frame around each pane of glass you wish to decorate. Tie up a piece of putty in a piece of thin muslin, leaving enough of the latter to hold instead of a handle. With this dabble all over that part of the glass which the pattern leaves bare. When the putty on the glass has dried, remove the paper and varnish the glass.

To Transfer Photographs to Glass. Separate the paper print from the background by steaming it, dry thoroughly and, having given the warmed glass an even coating of balsam or negative varnish, place the face of the print on the surface thus prepared. Smooth it out and let it stand in a cool place until the varnish has hardened. Then apply water, and with a soft piece of gum rubber rub off the paper so as to leave the photographic image on the varnished glass.

Platinizing Glass. In order to succeed in coating porcelain or glass with a perfectly faultless film of platinum of the brilliancy of silver it is indispensable to make use of a perfectly dry chloride of platinum, as free from acid as possible. To that end pour some oil of rosemary over the perfectly dry chloride of platinum in a small porcelain mortar and knead it up with the pestle, renewing the oil about three times; and continue this operation until there is produced from the brownish-red chloride a black plastic mass, wherein no particles of undecomposed chloride of platinum can be ound. The oil of rosemary assumes

hereby a more or less yellow color, in consequence of partially taking up chlorine from the chloride of platinum. When the whole of the chloride of platinum is thus reduced, and after pouring the oil of rosemary off, rub it up well with the pestle with about five times its weight of oil of lavender until it has become a perfectly homogeneous, thin fluid. Then after leaving it to stand for half an hour or so apply the mass as uniformly as may be and in the thinnest possible layer to the object of porcelain, earthenware, or glass by means of a soft, delicate brush. The thinner the coat of the application the more brilliant the film of platinum. All that is required further is to subject the articles for a few minutes to a very low, scarcely perceptible red heat, either in a muffle or in the flame of a Bunsen's gas-blowpipe used with caution. The articles receive from this baking a beautiful lustre as brilliant as silver. If, by an oversight, the coating of platinum upon the articles has turned out faulty, or if breakages occur during the baking, every trace of the metal can be recovered from the objects. Nothing more is required than to pour common hydrochloric acid over them and then touch them with a zinc rod. In consequence of the hydrogen evolved, both at the upper and lower surface of the film of platinum which acts as the negative pole, the shining metallic coating instantly peels off in the form of extremely thin leaves from the base of porcelain or glass and, notwithstanding the specific gravity of the metal, these ascend partially and float on the surface of the acid. On separating the hydrochloric acid by the use of a filter the whole of the platinum is recovered. One should prepare only as much of the platinizing fluid as is required for immediate use, as it loses in efficiency by keeping.

Toughened Glass. In this process the red-hot glass is dipped into a warm bath consisting of water and starch, or gum kept at 212° F. It is taken out again when the red glow has almost gone, and is then allowed to cool in an oven kept at a slightly lower temperature than the glass. Any article of glass can be treated by this method,

of cream.

Caoutchouc Lubricant for Drivingbeits. One-half pound of rubber in small pieces and pint of oil of turpentine are brought into an iron boiler, tightly covered with a lid, and gently digested over a coal fire, until the rubber is melted. Then add 14 ounces of rosin, stir thoroughly, melt again, and add in the same manner 14 ounces of yellow wax. Stir the mass occasionally while melting. Next heat in a large pot 3 pounds of fish oil and pound of tallow until the tallow is melted, and then add with constant stirring the first mixture, while still hot. Continue stirring until the mass solidifies. For use, the lubricant is applied with a brush to both sides of old, cracked belts, in the sun or a warm room, and allowed to dry. The durability of new or good belts is much increased by an occasional application, while running, of a small quantity of the lubricant. Instead of caoutchouc, old rubber waste can also be employed, but it must first be boiled with soda-lye for to hour, and instead of about pound must be used. Harness Grease. Ammonia soap 4 parts, palm oil 1 part, ordinary hard soap 3 parts, solution of tannin (9 to 16 parts of tannin in 4 of water) 12 parts. Melt the oil and soap together, add the ammonia soap, then the tannin solution, and stir thoroughly. The preparation will keep for some time if kept in stone bottles well corked. In greasing, no more grease should be used than the leather will absorb.

pound

The ammonia soap used in the preparation is made by heating oleic acid to the boiling point and adding sesquicarbonate of ammonium until the odor of ammonia no longer disappears.

Harness Polish. Four ounces of glue, 1 pints of vinegar, 2 ounces of gum-Arabic, pint of black ink, and 2 drachms of isinglass. Break the glue in pieces, put it in a basin, and pour over it about 1 pint of the vinegar; let it stand until it becomes perfectly soft. Put the gum-Arabic in another vessel, with the ink, until it is entirely dis

solved; melt the isinglass in as much water as will cover it, which may be easily done by placing the cup containit is wanted for use. To mix them, pour the remaining vinegar with the softened glue into a dish over a moderate fire, stirring it until it is entirely dissolved, being careful not to let it reach the boiling point, that it may not burn the bottom, about 182° F. being the best heat. Next add the gum; let it arrive at about the same heat, and then add the isinglass. Take from the fire and pour it off for use.

To use it put as much as required in a saucer, heat sufficiently to make it fluid, and apply a thin coat with a dry sponge. If the article is dried quickly, either in the sun or by the fire, it will show the better polish.

Thurston's Machine for Testing Lubricating Oils. Prof. R. H. Thurston, whose investigations on this subject are of much importance, has devised several machines for the determination of the value of lubricating oils. The form shown in Fig.75 is designed for testing oils used in railway service, and for all other purposes where it is important to reduce to a minimum the friction of bearing surfaces under heavy pressures. With its use it is possible to determine which is the best and consequently the cheapest oil for lubricating purposes, a matter of great importance in respect to the question of the economical use of power. The principle of the machine will appear from the following description, viz.: It comprises a spindle revolved in horizontal bearings by a belt from the main shaft of the workshop. On the overhanging end of this spindle is formed a journal, from which is hung a heavily-weighted rod. The two halves of the bearings in this rod by which it hangs on the journal are pressed down upon the journal with any desired pressure by means of a spiral spring placed in the centre of the rod. The weight of this pendulum prevents it revolving along with the spindle, but the friction at the journal deflects the pendulum from the vertical through an angle whose line is a measure of the frictional effort. There is also inserted in the bearings a thermometer, by which the effect of the friction in