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tection which prevented continual renewal of the surrounding medium, as when inclosed by brickwork or masonry. In fresh water it suffered no such deterioration, and under ordinary circumstances its durability in a pure atmosphere appeared unlimited. In the case of zinc, although the bright metal oxidized even more rapidly than iron, yet the oxide adhered with such tenacity to the metal, that it afforded an efficient protection against the continuation of the process. To this property the metal owed its great durability, more especially as its oxide was insoluble in water. In the presence of any solvent of the oxide, this metal was so speedily destroyed as to be prac tically useless, unless protected by paint. The destruction of zinc in smoky districts was, however, principally due to galvanic action. A similar action produced the rusting away at the base of iron railings, when fixed in stone work, as was usually the case, by being run in with lead. The contact of copper with the iron plates of a vessel was also a source of a great danger; and there were numberless other in stances, in which the contact of metals of different conducting powers was equally destructive. In all such cases the use of paint furnished, at any rate, a temporary remedy. It was difficult to over-estimate the value of the introduction of the process of coating iron plates with zinc, by simply cleaning and immersing them in the molten metal. All that had been said on the subject of zinc applied equally to galvanized iron, as it was called. In a clear atmosphere its great durability, its stiffness, its freedom from expansion, and its economy, were all qualities of the highest value; while, on the other hand, without constant painting, it was wholly un fitted for the atmosphere of smoky towns, or manufactories, or even stations where it was exposed to the fumes from locomotives. Both the corrosive and the galvanic actions, which in such cases were so destructive, did not cease with the destruction of the zinc, which was soon effected, but continued also to act, with fatal effect, upon the iron itself, as might be seen in many railway stations and sheds near manu facturing towns. The corrosive tendency in zinc and iron obliged the use of the less oxidahle metals, copper and lead. Lead slowly absorbed oxygen and carbonic acid in moist air. It was acted upon by certain waters, and was occasionally riddled with holes by the larva of an in sect ; and its expansion and contraction required to be carefully allowed for in its use. Its ductility rendered it a valuable material. Copper might, however, in many instances, be used with great advantage in its stead. The action of sea water on copper was so important, that it was par ticularly alluded to. The object in covering a vessel with copper was solely to prevent the adhesion of barnacles and other molluscs. This property was not due to the poisonous quality of its salts, as was some times asserted, nor was copper used on account of its durable qualities; on the contrary, its value depended on its slow destruction. The chlo ride of copper formed beneath the attachment of the barnacle being a soluble salt, the creature no sooner effected a lodgment than it was at once set free by the solution of the salt; while the salts which formed on zinc or iron being insoluble, the plate was rather protected than otherwise by the tenacious parasite. Hence the difficulty of devising an efficient paint for iron ships; for while, on the one hand, it must be slowly soluble in water to prevent this adhesion, it must, on the other hand, be sufficiently insoluble to be durable. Ordinary oil paint was the most efficient material for protecting either metals or wood from the effects of moisture and air; but all oils, resins, and gums exposed to air, and especially to the light of the sun, oxidized and burnt away with more or less rapidity, leaving a powdery residue behind. As a preservative of paint against the heat of the sun and light, attention was directed to the virtue of a coating of silicious sand, dredged on the paint while wet. The durabiliiy of matter was a subject of the highest philosophical interest. The universal law on this planet appeared to be, that no form should be permanent. Never-ceasing destruction and re-construc- tion were characteristic, within the range of the atmosphere, of every thing that existed, whether as regarded organic life or inorganic matter; and it was probable that even the atmosphere itself was subject to the same decree. ♦ Oxyhydrogen Light.—The experiments commenced last year on the Place de 1’Hotel de Ville, in Paris, on the oxyhydrogen light, are about to be continued, by order of the Emperor, in the Court of the Tuileries. The magnesia cylinders having been found to corrode and waste away too rapidly for the purposes of a continuous light, an artillery officer, AL Caron, after experimenting with a variety of sub stances, has adopted zircon, a substance which Berzelius pointed out as infusible, and giving forth a very brilliant light under the blowpipe. It is said that M. Caron has had a cylinder of this substance in use with the oxyhydrogen light for a month without the slightest trace of volatilization. The luminous power of zircon, under the oxyhydrogen jet, is about one-fifth more than that of magnesia. The zircon em ployed is an oxyde of zirconium; it is found principally near Miask, at the foot of the Ural mountains. M. Caron economises the zircon, by mounting a point of it on a small stick of magnesia or fire-clay, the zircon being made to adhere by compression and afterwards baking. THE BENEDICTINE CHAPEL, NICE, FRANCE. ( With an Engraving.) The accompanying Plate exhibits the interior of a small chapel in course of erection at Mont Boron, Nice. The building consists of a nave, with an apsidal retro-choir 26 feet broad. The choir is attached by a corridor to a nunnery, separated from the main body of the chapel by a reredos flanked by open iron grilles. The chapel stands on a very prominent position, and is built of granite excavated from the rock on which it stands. The dressings, both exterior and interior, are of Arles sandstone. The roof is to be covered with red tiles. The amount of the contract is £1,200, exclusive of a sum for the frescoes, the altar, and stained glass, which it is expected will cost about £400 more. The work is being carefully carried out from the designs and under the superintendence of Mr. T. T. Smith, architect, Bloomsbury-square, London, who is, we understand, building extensively in the South of France. HOW TO VENTILATE A HOUSE. By S. Egan Rosser, Engineer. The object of this little treatise is not to investigate the methods adopted in the warming and ventilation of extensive public buildings, or even large mansions, but to consider how ordinary dwelling houses in towns, and country houses of moderate extent, may be comfortably warmed and efficiently ventilated. The open fire-place is the general and almost universal ex pedient for warming and ventilating English houses; but the inefficiency and disadvantages of the open fire, not only as a ventilating agent, but as a means of warming rooms, have been so strongly insisted upon by the majority of writers on this subject, that it may appear almost presumptuous to attempt its advocacy. If it should appear however, that the open fire is really consistent with the best arrangements for warming and ventilation, the strong hold which it unquestionably has in the habits of our people will render the public more favourably dis posed to anything that tends to increase its utility. The various “ ventilators ” and ventilating contrivances that are advertised on all sides may be more or less applicable accord ing to circumstances, and many of them are very useful in their way. It should be observed however, that none of them affords in itself, a complete means of ventilation, however useful each may be as forming part of a system. None of them is constantly and invariably efficient and complete in itself, as a means of ad mitting fresh and discharging vitiated air. Some of them are, from their nature and construction, admittedly capable of per forming only half the duty of ventilation. Such are Dr. Arnot’s chimney-valve, an excellent contrivance for promoting the escape of vitiated air ; and, Sherringham’s ventilator, which admits air from the exterior. The contrivances which profess to establish a double current will generally be found in practice to resolve themselves either into inlets or outlets, according as the evacua tion or influx of air by other channels is predominant. These observations are not urged as objections to the use of such ventilators, but simply to guard those who adopt them from expecting too much from them. It is not probable that the art of ventilation will ever be reduced to such an exact state, that good ventilation can be commanded by the use of any single instrument or contrivance. Efficient ventilation will probably continue to be, what it has hitherto been, the result of combination; not to be effected only in one particular mode, or by anybody’s patent; but by the intelligent application of general physical laws, ac cording to the circmnstances of each case. In domestic structures we have in the ordinary chimney flue a more valuable instrument of ventilation than any of the “venti lators ” hitherto contrived ; and this instrument is one which is provided as part of the building, is found in almost every room, and its use is familiar to all. For ordinary apartments the chimney affords a sufficient means for the extraction of the vitiated air when properly applied. It was calculated by the late Mr. Sylvester, that taking the average of London houses, the velocity of the chimney draught amounted to 6ft. per second. This calculation is confirmed by the observations of the Commissioners appointed for improving the sanitary condition of barracks and hospitals, whose experiments at the Wellington Barracks gave a velocity of 6.2ft. per second as the average draught of the chimneys.
