those ingredients which are required for the formation or healthy life" of the plant-tissues. In "How Crops Grow," the evidence is given which forces us to the conclusion that silica is unessential to the growth and perfect development not only of leguminous plants, but of all the various cereals, although the latter, when they grow in the soil, do contain 2.5 per cent., more or less, of this substance in their foliage. If silica be taken up by legumes and by corn-crops which are able to grow to perfection of parts and fulness of dimensions in its absence, then, certainly, "because the tissues want silica is no explanation of how they get it;" but saturation of the cell-juices does explain how a limit is put to the influx of this body into the plant from the soil.
S. W. Johnson.
Probable Cause of Boiler-Explosions.—Some six years ago, Mr. W. F. Barrett, F.C.S., observed that a red-hot ball of copper, on being immersed in a light solution of soap in water, entered the liquid without hissing or visible generation of steam. In a paper read before the British Association, he tells of sundry experiments, made with a view to investigate this phenomenon, and thinks that it probably accounts for many otherwise unaccountable explosions of steam-boilers. After experimenting with sundry red-hot metals in soap-water, he tried water without soap; but then the hissing was loud, and the evolution of steam copious. He next dissolved in water several soluble substances, and found that albumen, glycerine, and organic liquids in general, facilitate the acquisition by water of the spheroidal shape, probably by increasing its cohesion, while bodies such as ammonia, which yield vapor readily, have the same effect, though in not so marked a degree. Oil, whether shaken up or floating on the water, has the same effect as soap. When the red-hot ball is lowered into the liquid, to a depth of a foot or more, it is seen to be surrounded by a shell, of vapor, bounded by an envelop resembling burnished silver. As the ball cools, the shell grows thinner, and finally collapses. This is followed by a report, and volumes of steam are emitted. The author adds: "I have heard that traces of oil get into the boilers of steam-engines, and there can be no doubt that dissolved organic matter often finds its way in. If in any way we increase the intensity of the water, we render it possible for a corroded boiler to give way under the pressure of the steam suddenly generated in the way I have indicated."
Practical Application of Singing Flames.—The "singing flame," which at first view might seem to be merely a curious phenomenon, is found to be, in fact, a discovery of very high importance for science and the useful arts. One of the latest applications of this principle is that made by Dr. A. K. Irvine, of the British Iron and Steel Institute, who makes use of the singing flame in the construction of a safety-lamp for mines. If an explosive mixture of inflammable gas and air be passed through and ignited on the surface of a disk of wire gauze too fine to suffer the flame to traverse it, and then surrounded by a chimney, to prevent air from entering, save through the gauze, the flame vibrates, and, the vibration being communicated to the ascending gases, produces a sound varying in pitch and intensity according to the height and calibre of the chimney. A lamp constructed on this principle will give timely warning to the miner whenever the atmosphere and the fire-damp are coming together in the proportions requisite for an explosion.
Science in the Household.—The application of science to the affairs of the household, both in the shape of improved processes and the introduction of labor-saving appliances, has already gone sufficiently far to warrant the expectation that from this quarter there will eventually come a solution of the problem of rational house-keeping, when the family will be largely rid of the annoyances incident to a state of dependence on incompetent and wasteful hirelings, and master of its own internal economy. Already the sewing-machine has wrought a revolution in the clothing department, which leaves scarcely a trace of its former wearisome tasks. The washing-machine and wringer, aided by various detergent preparations, have in like manner greatly lightened the work of the laundry, making the destructive and exhausting labor