THE MONTH:
SCIENCE AND ARTS.
The paragraphs on the use of zinc as a preventive of scale in steam-boilers, in the Month for March last ([ante 207]), have brought us many inquiries for further particulars. One correspondent wishes to know what length of time the lump of zinc will last? to which we answer, that on this point there is nothing more precise in the original Report than that the zinc lasts the usual time of working the boiler between the periods of cleaning. The zinc is more efficacious in the form of an ingot or solid lump, than when small heaps of clippings are employed; and we cannot imagine that it would be difficult for any intelligent person to determine by observation the dissolution of the zinc.
The theoretical explanation of the preservative action is, that in the process of oxidation the zinc borrows oxygen from the air dissolved in the feed-water only. The two metals, zinc and iron, surrounded by water at a high temperature, form an electrical ‘pile’ with a single liquid which slowly decomposes the water. The oxygen flies to the most oxidisable metal, the zinc, while the hydrogen is set free on the surface of the iron. This release of hydrogen goes on over the whole extent of the iron in contact with the water, and the minute bubbles of this gas isolate at each instant the sides of the boiler from the incrusting substance. If the quantity of this substance is small, it becomes so penetrated by the bubbles that it remains soft as mud; and if in greater quantity, coherent incrustations are formed, but in such a state of isolation as to be readily separated from the iron.
This remarkable action of zinc was first discovered in 1861, during the repair of a steam-vessel at Havre; and since then it has with approval been taken into use in some of the large manufacturing establishments of France. Readers desirous of consulting the original Report will find it in the Bulletin de la Société d’Encouragement pour l’Industrie Nationale, No. 51, March 1878, which may be obtained through Messrs Trübner, the well-known London publishers, or any foreign bookseller.
The Institution of Mechanical Engineers have published their usual yearly list of subjects on which they would be glad to have papers for reading at their meetings. As may be supposed, their scheme includes all branches of mechanical engineering; but we mention a few as likely to occupy the attention of some of the many ingenious artificers who are always inventing or improving. For example, there are hot-air engines, engines worked by gas, and electro-magnetic engines. Corn-mills, results of working with an air-blast and ring-stones. Flax, lace, and knitting machinery. Wood-working machines, for morticing, dovetailing, planing, rounding, surfacing and copying. Paper-making and paper-cutting machines. Machines for printing from engraved surfaces, and type-composing and distributing machines. Best plans for seasoning timber and cordage. Ventilation of mines. Prevention of rust in iron ships and tanks; and a way to diminish the dead-weight in railway trains.
One of the subjects is improvements in lighthouses; by which we are reminded that a new lighthouse at the Eddystone is talked of. The present structure was built by Smeaton in 1756-59; and ever since, as long before, as indicated by the name, the sea has been wearing away the rock on which it stands, and now threatens to undermine the foundations. The new tower would be built on an adjacent rock with, as we may easily believe, all the best improvements in construction and lighting.
Descriptions have been given at meetings of the Institution of machines for pressing cotton in bales for shipment. Some machines will press twice as much cotton into a bale of given size as others; which effects an important economy as regards stowage and in cost of packing, for it is estimated that the outlay for fuel for the pressing engine amounts to only a penny a bale.
Messrs Siemens’ improvements in the dynamo-electric machine appear likely to settle the question as regards transmission of mechanical power to long distances. Given the power to work one machine, it can be transmitted by wires to a second, from that to a third, and so on continuously through many miles. A waterfall or steam-engine of one hundred horse-power working the first machine in the series would produce fifty horse-power at a distance of thirty miles. Hence it would be possible to grind wheat, to shape iron in a lathe, to saw wood, or weave cotton by machinery, in a district where all the coal was exhausted. This consideration ought to be appreciated by the people who imagine that our coal-fields will all too soon be dug completely out. Another advantage of the dynamo-machine is that if thrown out of gear for a few minutes or for a longer time there is no loss or waste of power.
Considering that slag can be made into glass, and that slag is a disagreeable encumbrance which many manufacturers would gladly get rid of, a suggestion has been offered that, instead of being made of metal, tanks and cisterns should be made of slag glass, in a single casting. There would then be no leaky joints, no unpleasant taste from paint or metal; cleaning would be easy; and if large dimensions were required, a number of small tanks might be placed side by side, and connected by slag-glass tubes. When this suggestion comes to be adopted, there will be no need to inquire about prevention of rust in tanks, nor to be timorous of lead-poisoning.