Изображения страниц
PDF
EPUB

nation has recently been made, the boilers having been in use for a year and a half. The steel boiler was found in excellent condition. It appeared that it evaporated 11.66 cubic feet per hour, against 9.37 by the common boiler, with about the same expenditure of fuel. Steel drills for shaft sinking are taking the place of the old iron drills steeled. Stamp heads for crushing ore have hitherto been made of cast iron, the fragments of which mixed with and contaminated the ore, often causing great trouble. A trial is now being made of steel stamp heads, doubtless with considerable advantage.

Aluminium.-Messrs. Mappin Brothers are exhibiting various articles in aluminium and its alloys. The main portions of the articles are usually formed of the aluminium-bronze, and a good effect is produced by relieving this with ornaments of "oxidized" aluminium whitened by the addition of a small amount of nickel. C. Fissier, director of the aluminium works at Rouen, shows that one per cent. of aluminium in copper makes the latter more fusible, giving it the property of filling the mould at casting. The copper gains in hardness and tenacity without losing its malleability. In transverse strength this alloy was found to be more than twice as rigid as either brass or copper. An alloy of one part of aluminium to a bronze of 96 copper and 4 tin has a fine colour and is very homogeneous. It does not oxidize in casting, and its transverse strength is two and a half times that of the original bronze, and after hammering four times the latter. At a recent meeting at the Royal Institution, Messrs. Johnson & Matthey exhibited an alloy of aluminium and nickel, containing one and a half per cent. of the latter, which has been tried by hydraulic pressure to 476 lb. to the square inch.

Zinc.-M. E. Gatellier, in endeavouring to account for the great loss of zinc in the smelting of its ores, finds that much is due to the porosity of the retorts in which the operation is carried out, and he succeeded in materially reducing the loss by applying a glaze to the exterior of the retorts by means of common salt-the same material that is employed in glazing in potteries. As a secondary advantage, he points out the less injury to the neighbourhood of the works from saving the zinc, which would otherwise escape into the atmosphere. Mr. George Darlington describes the preparation of zinc-white (oxide of zinc) direct from the ore, as it is now practised in America, where the make is from 8,000 to 10,000 tons annually. The furnaces are similar to coke ovens, with flues leading to collecting rooms and chambers of subsidence. The principle adopted is to evolve the zinc in the metallic state by the action of the fuel (anthracite) upon the ore; as it rises in vapour it finds oxygen at a very high temperature, and is thus converted into oxide. Zinc-white is now in great request as a pigment, as a substitute for white lead, over which it has many advantages.

Platinum.-At a scientific meeting held at Bonn, in the beginning of April, M. von Dechen produced two fragments of crucibles in which platinum had been fused with coke by Dr. Carl Bischof. There was evidence of its perfect fusion, and of the great ductility secured. The crucibles were made of clay occurring in the coal-measures of Waldenburg, in Silesia, discovered by Dr. Bischof in his researches on fireproof clays.

Platinum cannot be fused in graphite crucibles, as the carbon unites with the metal, making it very brittle. Messrs. Johnson & Matthey have prepared specimens of autogenous soldering in platinum, with tubes of the same, having cast iron and leaden screw joints for use with sulphuric acid at high temperatures.

MINING.

Blasting.-The Italian Minister of Public Works has reported on the progress of the Mont Cenis tunnel. Boring machines are now used at each end, worked by compressed air. In 1862, to pierce 380 metres on the side of Bardonnèche, 45,751 holes were bored, from 75 to 80 centimetres (30 to 32 inches) in depth; 72,538 borers were set to work; there were 54,875 blasts, and 1,334,000 cubic metres of compressed air were consumed, equal to 8,004,000 cubic metres of atmospheric air. It is expected that at the present rate the tunnel will be completed in 12 years.- -In consequence of the many accidents from ordinary blasting, the far safer plan of blasting by electricity is gradually commending itself to the mining public. It has long been used in military mining with success, and also in civil engineering, where large masses of rock had to be moved, since several charges may be fired at precisely the same moment. Thus, a few months ago, a large martello tower which guarded the entrance to Chatham harbour was demolished. The charges of powder were each 40 lb., distributed at equal distances beneath the foundations; the whole being connected by wires. In this kind of blasting a pair of wires, united at the extremities by a very fine one of platinum, is placed in the interior of the charge of powder. A current of electricity is passed by a magneto-electric machine. The wires may be of any length, and thus the workman may place himself out of danger. Moreover, if the charge miss fire there is no possibility of any smouldering spark, as in the case of the ordinary fuse, which has led to many accidents from this cause.

Ventilation.-It may be remembered that at the time of the late accident at Risca, the ventilating power was a machine. Immediately afterwards a larger machine was erected; mechanical ventilation being still preferred to that produced by the furnace. Lately, the machine got out of order, and a furnace has been erected to supersede it. English mine engineers, as a rule, consider furnace ventilation preferable to mechanical, whilst the majority of continental miners hold the opposite opinion. Mr. Rogers, of Farnley Wood Colliery, near Leeds, has adopted for ventilating power the heat of coke ovens, which may be placed either at the bottom of the upcast shaft, or at the surface. The system is said to work admirably; and at the same time coal slack, unsaleable at 1s. per ton, is converted into good coke worth 5s. per ton.

Testing Air in Mines.—Mr. W. Keene, the Government examiner of coal fields in New South Wales, has invented a simple apparatus for estimating the salubrity of the air in mines. It is a closed tin box with a glass window in one of its sides, and containing a candle holder. A candle is lighted and inserted, after which the box is closed. It is then seen how long the candle burns; the length of time being proportional to the amount of oxygen in the air examined. Thus, in a particular case, with a vessel

holding a cubic foot, the candle burnt 6 minutes. In a coal mine, where the air is vitiated, it would not burn so long; and Mr. Keene proposes to prohibit working in places where the candle will burn not more than three minutes.

Safety of the Davy Lamp.— At a late meeting of the North of England Mine Engineers, the President, N. Wood, Esq., stated that at a particular colliery, the workmen always made the gauze of their lamps red hot before using them, in order to expel the oil contained in the wire. Rough experiments had been made, and it was found that new gauze was sometimes capable of passing the flame of gas in consequence of the oil it contained, and which is used in the manufacture of the wire. This may account for explosions which have taken place under mysterious circumstances, and when the lamps have appeared in good condition. Whenever a lamp shows any indication of explosive gas, it should be instantly withdrawn; if this precaution is attended to, the Davy may still be considered a safe lamp. Further experiments are to be made.

PHOTOGRAPHY.

THE

THE principal novelty in the way of photographic materials which we are called upon to notice, is the so-called " enamel paper," intended to be used in printing as a substitute for that prepared with albumen. The new article appears to have been originally manufactured in Germany, but already there are several kinds known in commerce ;-all of them are, however distinguished for their fineness of texture and the extreme lustre of their surfaces-peculiarities attributable to the employment of mineral pigments, conjointly with albumen, in their preparation. With regard to their exact nature many statements have been made, and the white pigment has been shown to consist sometimes of sulphate of baryta, and in other samples of oxide of zinc, with albumen in all cases as the adhesive material, and a soluble chloride to furnish the necessary elements for the production of the photographic image. The paper is rather thick, and requires to be manipulated in the same manner as the common albumenized material, with the additional precautions of allowing a somewhat longer interval for the final washing of the prints, and taking care not to crease or fold the enamelled surface, which is somewhat sensitive to incautious handling. Varieties of this enamelled paper may be procured in several tints of colour; among others, pale lilac or rose-pink, serving in the representation of subjects where a degree of warmth of tone is appropriate. This description of paper appears generally suitable for cartes de visite, stereoscopic pictures, and others of diminutive size; but the excessive brilliancy of the enamelled surface is, for larger subjects, eminently distasteful.

A suggestion relative to the employment of ammonia for the purpose of "fuming" the sensitized surface of papers used in the printing processes has not yet been entirely disposed of; some authorities adhering to the opinion that such treatment confers great advantages on the score of rapidity of action, as well as in the toning process and subsequent mani

[ocr errors][ocr errors]

pulation. The difficulty in securing uniform results, and the inconvenience arising from the diffusion of ammonia gas into the atmosphere of the operating-room are, on the other hand, manifest disadvantages.

The double sulphate of iron and ammonia has taken a permanent position in the list of chemical salts required in photography. As a developing agent this solution answers admirably, whilst it is less prone to oxidation than the simple sulphate. The formula of this compound salt, FeO, SO,, NH, O, SO, + 6 HO, indicates a higher atomic value than the crystallized sulphate of iron, FeO, SO, + 7 HO, and a proportionately larger amount by weight must be employed in consequence. For its preparation, two parts of sulphate of iron and one of sulphate of ammonia may be dissolved together in four or five parts of hot distilled water; on cooling, the double salt will crystallize out, and the supernatant liquid may be again used for the solution of further quantities of the individual salts. The crystals, drained and dried on blotting-paper, are still liable to be affected by exposure to air, but in stoppered bottles, and with ordinary precautions, they may be preserved for a long time unchanged. The aqueous solution soon acquires a pale brownish tint, which does not, however, appreciably affect its properties as a reducing agent. When required for the development of collodion negatives, the following formula may be adopted :

Sulphate of iron and ammonia

Acetic acid

Alcohol.

Water.

25 grains

15 minims

quant. suff.
1 ounce.

The addition of alcohol is merely for the purpose of causing the liquid to flow evenly over the plate; the quantity usually sufficient would be about thirty minims.

M. Meynier's proposal in reference to the employment of the sulphocyanide of ammonium as a fixing agent, has been favourably reported upon by a committee consisting of MM. Périer, Bayard, Girard, and Davanne, and by others in this country; but the encouragement of low cost is yet wanting as a stimulus to further experiment and more general application.

The composition of photographic prints, as regards their metallic constituents, is still under discussion. Dr. Schnauss maintains that in a properly fixed and toned print, there should not be any silver remaining, but that the whole of this metal is ordinarily dissolved out, and replaced by gold in the successive operations of toning and fixing the proof. MM. Girard and Davanne, Dr. Van Monckhoven, and Mr. Spiller, assert on the contrary that this substitution is not completely effected, and that under all circumstances a fair proportion of silver remains in the proof, and may easily be detected, by chemical analysis, in the ashes left on burning the paper.

Mr. H. Cooper gives the following instructions for the preparation of a kind of gelatino-resinous paper, suitable for printing purposes ::-Dissolve sheet india-rubber or gutta-percha in chloroform, and add to it benzole in such proportion as will make a solution of three grains to the ounce;

immerse the bottle in hot water and agitate occasionally until completely dissolved. When cool, the solution is poured into a flat dish, and sheets of paper immersed therein, and after a few minutes removed, drained, and dried; they are then salted by floating upon a solution of chloride of sodium (ten grains to the ounce of water), to which a small quantity of Iceland moss has been added. In order to sensitize this paper, it is treated in the usual manner with a 60-grain solution of nitrate of silver.

The recovery of gold and silver from the waste solutions and products of a photographic laboratory has been proved by Mr. England to furnish very lucrative results; many pounds' weight of an alloy of these precious metals having been recovered from the various residues obtained in the printing operations carried on at his establishment. The paper read by that gentleman at a meeting of the London Photographic Society, on the 5th May, details the steps to be taken in order to effect this saving.

The partial eclipse of the sun visible on the 17th May last, and the total eclipse of the moon on the night of the 1st June, were events which do not appear to have claimed from photographers the amount of attention which such interesting occurrences undoubtedly deserve. Among the records of the solar eclipse which have come under our notice are those of Mr. W. Deane, taken at Richmond, and a series of five larger representations which were photographed at Woolwich by Mr. Spiller. The appearance at the moment of maximum obscuration is well shown in the latter series, whilst Mr. Deane's picture shows likewise a peculiar kind of solar radiation, which assumes somewhat the figure of a cross.

The remarkable photographic observations made by Mr. Glaisher during his last balloon ascent excited a great deal of attention; the principal fact may thus be stated: At an altitude of three miles, with the thermometer registering 21 degrees Fahrenheit, and in the clear atmosphere above the clouds, it was found that sheets of sensitized photographic paper were less affected in colour during thirty minutes' exposure than were similar papers held in the sunlight at about the same time, but for one minute only, within the grounds of the Royal Observatory, Greenwich. Many opinions have been offered by way of accounting for these curious results; and it seems generally admitted that the dry condition of the air would naturally induce a state of inactivity in consequence of the removal from the paper of water, which is so necessary in all these cases for the purpose of aiding chemical decomposition, upon which the darkening in colour depends. In apparent contradiction to these results are the former observations of Professor C. Piazzi Smyth, who states that during his ascent of the mountain in Teneriffe he remarked a gradual increase of chemical activity just in proportion as he gained in altitude; and that in using the camera near the summit he found that the exposure might be very much curtailed. To settle this apparent discrepancy Mr. Negretti recently made an ascent from Sydenham in Mr. Coxwell's mammoth balloon, taking with him a camera and all the materials requisite for carrying on the practice of the collodion process; the car itself being fitted up as an operating-room. He likewise found that the time of exposure at great altitudes might be very much shortened. It thus appears that in the camera, as in all cases where it is impossible for the water to evaporate from the film or other

« ПредыдущаяПродолжить »