SCIENTIFIC

Otago Witness, Issue 1926, 15 January 1891, Page 41

SCIENTIFIC

— Soot is very often seen to gather on the outside of chimneys. A correspondent of the Boston Journal of Commerce says that he has a chimney 150 ft high covered with soot from bottom to top, and asks the cause. That journal answers as follows :— " One of the products of combustion is water formed by the union ef hydrogen and oxygen in the fuel when present in the proper proportion. This water escapes in the form of vapour, and some of it is condensed on the inside of the chimney. The brick being porous absorbs the water, which works its way through to the outside, carrying soot with it by capillary attraction, and, in time, enough appears to be observable on the outside. Where wood is used for fuel this should show more plainly, owing to the considerable amount of water appearing about the furnace and connections when wood is burned."

—It is stated that the Austrian Hydrographic Bureau adopts the following method of making paper transparent for copying drawings. The sheet of paper being placed over the drawing to be copied, it is lightly rubbed with a ball of cotton saturated with pure benzine. The tracing can then be readily made, owing to the resulting transparency, and the benzine on evaporating' leaves the paper opaque as befoie, and without any trace of odour. Absolute purity of the benzine, however, must be insisted upon to secure good results. — Olzewski, the Russian physicist, has, succeeded in liquefying sufficient ozone to determine the boiling point, which is 159 Fahr. The liquid ozone is dark blue in colour, and is nearly opaque in a layer of a tenth of an inch thick.

— The following interesting record is from the London Electrician: — "An experiment described by M. J. Borgman has an important bearing upon the explanation of the remarkable discovery of M. Hallwachs, in which a beam of light seems to act as a conductor for an electric current. The latter experiment consisted in placing a piece of metallic gauze parallel with, but insulated from, a second sheet of metal. The first is connected with the positive, the second with the negative pole of a battery, and in one of the leads a delicate galvanometer is placed. If, now, a beam of light be made to pass through the gauze, and to fall on the plate behind, a current is set up in the circuit, and continues to flow as long as the illumination is maintained. It has moreover been shown that the action is due to the ultra-violet waves. Now, M. Borgman wanted to ascertain whether or not the effect was instantaneous ; that is to say, whether the commencement and cessation of the current was or was not simultaneous with that of the illumination. M. Borgman probably reasoned that, if the beam acted in some sense as a conductor of the current, the effect must be instantaneous; while if the phenomenon resulted from some secondary action, it would probably go on increasing up to a certain point with the duration of the illumination, and it would also probably continue for a" time after the light had been cut off. His method of making the test was equally simple and ingenious. The light was interrupted at rapid intervals by means of a rotating disc with holes or slits, and he placed a telephone in circuit with the battery. It is, then, obvious that, if the effect "is instantaneous, the telephone will produce a note corresponding in pitch to the velocity of the disc ; if otherwise, there will be silence. There was silence. A make and break in any other part of the circuit could be heard, but not in the beam of light; hence we must seek for some secondary action on the surface of the plates to explain M. Hallwach's experiments." — From time to time hints have been given out as to the feasibility of flooding the great desert of Sahara, which some maintain is considerably below the level of the Mediterranean Sea. If this is a fact, it appears at the first glance to be comparatively easy. In the thousands of miles of sea-bound coast, one would think a spot of low level could be found to admit the water on a large scale, which in time might overcome evaporation, and rising above and covering the sandy desolation, change the desert aspect to a clime of health and beauty on the higher lands. There are many considerations which should be taken into account before such a great engineering feat is undertaken. First, what amount of evaporation would be carried on over such, a vast area of the earth's surface 1 W^at would be the result of such a great weight brought to bear on a. fresh locality? Would it have any appreciable effects on the earth's rotation ? Would the cooling which might be occasioned lead to any serious agitation in the air 1 Are the lower levels of the desert inhabited to any great extent? What are the respective levels of the Red and the Mediterranean Seas and the Atlantic Ocean 1 The area of the desert is about 2000 miles in longitude by 1000 in latitude. The proposed connecting canal or route of inflow from the Mediterranean is about halfway of the distance of [the desert in its longitudinal direction. — The wonderful advance of electrio lighting in America during the past few years explains why tl c price of platinum has advanced to such an extent that it is now about as valuable as gold. Five years ago the metal was seldom employed, except in the evaporating stills for the concentration of sulphuric acid, and in the manufacture of jewellery. It was then to be bought in the rough for 3dol 'to sdol an ounce.- A year ago it advanced to Bdol an ounce, six months later it had risen to 14, and now it has gone up to 20. Platinum gets its name from the Spaniards. As early as the sixteenth century it appears to have been noticed that the gold ore in the Spanish mines of Darieh included grains of a white metal endowed with the qualities of a noble metal, and yet distinctly different from silver. Its exportation to Europe was prohibited, because the Spanish Government found that it might easily be used in the adulteration of gold. For this reason it did not find its way to Europe until the middle of the last centuryj when it was known as " platina del Pinto "— the little silver from the River Pinto. Since its remarkable chemical properties were established in 1780, it has been discovered in New Grenada, San DQmingo, California, Borneo, and in portions of Canada, But the

richest deposits axe those in the Ural Mountains, where the metal was discovered in 1823, and where it has been successfully mined by the Russians since 1828.

— A smoke-consuming apparatus has been adopted by the corporation of Leeds, in connection with two boilers for the public refuse destructors. The chief feature of this new apparatus is that the furnace is so constructed as to burn in a downward direction. Ordinary fire-bars are not used. By a descending draught th 6 smoke, thoroughly saturated with oxygen, is passed through the mass of incandescent flame, the hydrocarbon gas being thereby burnt and destroyed, and the flame converted into carbonic acid gas before it enters the flue.