an alarm-bell, operated by clock-work, which goes into action as soon as the wire is slacked. By changing the tension of the copper-spring, the instrument may be set to go off at any temperature, indicated by a dial and pointer attached to the regulatingscrew. When exhibited to the meeting, the instrument was started by holding it, for a moment, over a gas-flame, and by the mere warmth of the breath.

Steam Generators. A novelty was exhibited, at the exhibition of the American Institute, by Thomas Mitchell, of Albany, N. Y. It is a cylinder of wrought iron with welded joints, into which water is thrown by a feed-pump; the same pump operating through a worm gear to slowly rotate the cylinder in the furnace where it is suspended upon two journals, one at either end of the furnace. The design is to only throw water into the revolving generator, as wanted, to make steam. The steam is generated under very high pressure. The water is injected through a corepipe in one of the journals which extends longitudinally through the axis of the cylinder, and is perforated at intervals throughout its length. The water is thus subdivided into small jets, which the heat of the cylinder converts into steam instantaneously.

A big Belt. The New York Belting and Packing Company have lately had on exhibition at their store, New York, an Indiarubber belt 4 feet wide, 320 feet long, and weighing no less than 3,600 pounds. It is intended for the main driving-belt of the largest grain elevator in Chicago.

The Joy Hammer. This hammer is peculiarly adapted for drawing down iron or steel, in which operation a rapid succession of uniform blows is required, with only a graduaÎ alteration in the force of the successive strokes.

It therefore becomes possible to dispense with the complication of separate valves, and thus remove much of the risk of derangement and source of wear.

In this instrument the ram contains openings which are brought by its own motion into communication with passages for the inlet and escape of steam, and thus cause its motion to be automatically reversed. The only valve in the hammer is the throttlevalve governed by a treddle, and by the adjustment of its opening both the rapidity and force of the blows is at the same time regulated. As many as 500 blows in a minute may be readily struck, and from the simplicity and solidity of all parts there is the least possible chance of derangement.

Safety Nitro-Glycerine. — We learn from the "London Mining Journal" that a series of interesting experiments for protecting nitro-glycerine were recently made at the Manorfield House. Ẩ small quantity of the material was put into a basin, and hot water was poured upon it, the result being that in two minutes the original oil sunk to the bottom, and (the surplus water being poured off) was run into a small phial ready for use. Into this the fuse (pointed with a percussion cap) was inserted, and fired, and the loud explosion testified to the unimpaired force of the nitro-glycerine thus recovered. It is obvious that by this invention this highly dangerous but very useful compound can be conveyed by

rail or ship, and be stored with perfect safety, and that it may be "recovered" in small quantities on the very spot where it is required for use, so as to avoid, in a great measure, the peril to miners or others who have to handle it in their operations.

Painting Zinc. A difficulty is often experienced in causing oil colors to adhere to sheet zinc. Boettger recommends the employment of a mordant, so to speak, of the following composition: One part of chloride of copper, one of nitrate of copper, and one of sal-ammoniac, are to be dissolved in 64 parts of water, to which solution is to be added one part of commercial hydrochloric acid. The sheets of zinc are to be brushed over with this liquid, which gives them a deep black color; in the course of from 12 to 24 hours they become dry, and to their now dirty gray surface a coat of any oil color will firmly adhere. Some sheets of zinc prepared in this way, and afterwards painted, have been found to entirely withstand all the atmospheric changes of winter and summer.

Very Durable Cement for Iron and Stone. M. Pollack, of Bautzen, Saxony, states that, for a period of several years, he has used, as a cement to fasten stone to stone, and iron to iron, a paste made of pure oxide of lead, litharge, and glycerine in concentrated state. This mixture hardens rapidly, is insoluble in acids (unless quite concentrated), and is not affected by heat. M. Pollack has used it to fasten different portions of a fly-wheel with great success; while, when placed between stones, and once hardened, it is easier to break the stone than the joint.

"Dingler's Journal" recommends as a lute for covering the corks of vessels containing benzine or any of the light hydrocarbons or essential oils, a paste made of finely-ground litharge and concentrated glycerine. The mixture is spread over the corks or bungs, and soon hardens. It is insoluble in the said liquids, is not acted upon by them, and is quite inexpensive, as the commonest kind of glycerine can be used.

A writer in "Comptes Rendus " says that if articles made of copper be immersed in molten sulphur having lamp-black in suspension, they assume the appearance of bronze, and can be polished without losing that aspect.

Treating Textile Fabrics. M. Pierre Armand Neuman, of St. Denis, Paris, treats textile fabrics with sulphuric acid, for the purpose of rendering them impermeable. By this process the fibres on the surface of the fabric are partially dissolved, and converted into a glutinous substance, without the fibres in the body of the fabric being destroyed. The fabric, after being passed through the sulphuric acid, is quickly washed and rinsed in water, to stop the action of the acid, and remove all traces of it, and it is afterwards dried, when the part which has been acted on by the acid, having impregnated and coated the fibres of the fabric, and filled up the interstices between the warp and the weft, will convert it into a parchment-like and impermeable material.

Effect of Steam Heat on Hay. - A correspondent from Rancocas, N. J., favors us with a specimen of hay-wrapping which had been on a steam pipe for 9 years; the pipe carrying steam at 55 lbs. The specimen is of a chocolate brown and very friable; but it

burns no more readily than well-dried fresh hay, although its appearance would seem to indicate great combustibility. We should have less fear of its ignition than of pine wood similarly carbonized. Scientific American.

The Hydraulic Scraping of the Torquay Water Main.—Mr. R. E. Froude, at the meeting of the British Association, read a paper on the operations which were rendered necessary by the continually decreasing supply of water, which resulted in raising the supply from 320 gallons, in 1864, to 564 gallons per minute in 1867, to 634 gallons in 1868, and to 660 gallons in 1869. The plan adopted was that of passing through the main a piston, armed with a scraper.

Average Duty of Cornish Engines. - An estimate of the average duty of this class of engines, based on observations made upon 18 engines during one month, shows the following results: They have consumed 1,377 tons of coal, and lifted 10.2 million tons of water 10 fathoms high. The average duty of the whole is, therefore, 50,100,000 lbs., lifted one foot high, by the consumption of 112 lbs. of coal.

Aluminium Bells. It appears that some Belgian manufacturer has just had a bell cast of aluminium, and with good results. It is of course extremely light, so that, though large, it can be easily tolled; its tone is reported to be loud and of excellent pitch. Aluminium is the most sonorous of all metals. Engi

neer.

A new Alloy, forming a beautiful white metal, very hard and capable of taking a brilliant polish, is obtained by melting together about 70 parts of copper, 20 of nickel, 5 of zinc, and 4 of cadmium. It is, therefore, a kind of German silver, in which part of the zinc is replaced by cadmium. This alloy has been recently made in Paris for the manufacture of spoons and forks, which resemble articles of silver.

How Oroide is Made. — Oroide, the beautiful alloy resembling gold, is a French discovery, and consists of pure copper, 100 parts; zinc or (preferably) tin, 17 parts; magnesia, 6 parts; salammoniac one half part; quicklime, one-eighth part; tartar of commerce, 9 parts. The copper is first melted, then the magnesia, sal-ammoniac, lime, and tartar in powder are added little by little, briskly stirring for about half an hour, so as to mix thoroughly; after which zinc is thrown on the surface in small grains, stirring it until entirely fused. The crucible is then covered, and the fusion maintained about 35 minutes, when the dross is skimmed off, and the alloy is ready for use. It can be cast, rolled, drawn, stamped, chased, beaten into a powder or leaves; and none but excellent judges can distinguish it from gold.

S. T. Clements, D.D.S., writes to the "Dental Cosmos" that although wax and resin, shellac, varnish, and liquid silex are recommended for mending plaster models, neither, in his experience, can compare with sandarac varnish. Saturate the broken surfaces thoroughly, and press them well together. Allow it to dry, and the model will stand all the manipulation required. Safety Envelopes. It is stated that the thick, tough sap, found

in large quantities in the leaves of New Zealand flax, may be converted into a gum for sealing envelopes, which, when dry, unites the surfaces of paper so thoroughly that no process of steaming or soaking will permit them to be separated again. For this reason, it is now being used in large quantities in England, in the preparation of what are called "safely envelopes." Paper from Shavings and Sawdust. — Dr. Matthiessen, a wellknown savant, now appears in the character of an inventor and patentee in England of an important improvement. He submits wood when in a state of division, such as shavings, sawdust, or disintegrated wood, to what is known as a rotting process, - that is to say, the wood in a state of division is steeped either in running or stagnant water, and is allowed to undergo a rotting or fermenting process, by which process certain constituents of the wood will be decomposed and removed, and the subsequent treatment of the residual ligneous fibre for the production of pulp or paper will be thereby rendered more economical, and the process of boiling and bleaching is more easily effected.

Ineradicable Writing. — A French technical paper, specially devoted to the art and science of paper manufacture, states that any alterations or falsifications of writings in ordinary ink may be rendered impossible by passing the paper upon which it is intended to write through a solution of one milligram (0.01543 English grain) of gallic acid in as much pure distilled water as will fill to a moderate depth an ordinary soup-plate. After the paper thus prepared has become thoroughly dry, it may be used as ordinary paper for writing, but any attempt made to alter, falsify, or change anything written thereon, will be left perfectly visible, and may thus be readily detected.

How to make Paper Transparent. - Artists, architects, land surveyors, and all who have occasion to make use of tracing-paper in their professional duties, will be glad to know that any paper capable of the transfer of a drawing in ordinary ink, pencil, or water-colors, and that even a stout drawing-paper, can be made as transparent as the thin yellowish paper at present used for tracing purposes. The liquid used is benzine. If the paper be damped with pure and fresh-distilled benzine it at once assumes a transparency, and permits of the tracing being made, and of ink or water-colors being used on its surface without any running." The paper resumes its opacity as the benzine evaporates, and if the drawing is not then completed, the requisite portion of the paper must be again damped with the benzine. The transparent calico, on which indestructible tracings can be made, was a most valuable invention, and this new discovery of the properties of benzine will prove of further service to many branches of the art profession, in allowing the use of stiff paper where formerly only a slight tissue could be used.

66

NATURAL PHILOSOPHY.

TYNDALL'S DISCOVERY.

"IT consists," to use his own words, "in subjecting the vapors of volatile liquids to the action of concentrated sunlight, or to the concentrated beam of the electric light; " and some of the results which he records are of such singular, almost inconceivable, beauty, that for this reason alone, and putting aside their important application to many atmospheric phenomena, and probably to art, they have a claim to be noticed in these pages.

He uses the experimental tube. It is connected with an air-pump and with a series of tubes used for the purification of the air, and at one end of the tube, which lies horizontally and is closed by plates of glass, is placed an electric lamp, so arranged that the axis of the tube and that of the parallel beam issuing from the lamp are coincident.

The substances whose vapors were passed into the tube, and there exposed to strong light, are known to chemists as nitrite of amyl, iodide of allyl, iodide of isopropyl, hydrobromic acid, hydrochloric acid, hydriodic acid. When these vapors are exposed to the above-described action, clouds of the most beautiful appearance, and at some points vividly iridescent, show themselves in the tube. When the nitrite of amyl vapor is mixed with a little air the cloud is white; but if air is freely admitted, and the nitrite vapor thus attenuated, the cloud varies in color from a milky-blue to a pure, deep blue. "There could scarcely," says the author, "be a more impressive illustration of Newton's mode of regarding the generation of the color of the firmament than that here exhibited; for never, even in the skies of the Alps, have I seen a richer or a purer blue than that attainable by a suitable disposition of the light falling upon the precipitated vapor. May not the aqueous vapor of our atmosphere act in a similar manner?"

The cloud yielded by iodide of allyl was extremely beautiful. The whole column revolved round the axis of the decomposing central beam, and was nipped so as to have an hour-glass appearance, while round the gobular dilatations delicate cloud-filaments twisted themselves in spirals. It also folded itself into convolutions resembling those of shells. When hydrogen is made the vehicle of this vapor, the cloud assumes a pearly lustre, such as Dr. Tyndall has often noticed in certain conditions of the atmosphere in the Alps.

The action of light upon the vapor of iodide of isopropyl occasions in the course of a few minutes some singularly graceful