Rensselaer Union, Volume 8, Number 10, Rensselaer, Jasper County, 25 November 1875 — Surface Adhesion. [ARTICLE]

Surface Adhesion.

Thp adhesion of surfaces is of much greater importance and of more general application in the economy of nature and in the production of a multitude of phenomena than appears at first sight. It produces not only the friction between solids in contact (without which it would be very difficult, if not impossible, to attain any stability), but also the retention of liquids against the surface of solids, without which we would be unable to moisten or lubricate effectively any solid surface. This surface adhesion between a liquid and a solid of course increases with the increase of the surface of the solid, and the most direct illustration of this is the fact that while, for- instance, solid stones sink rapidly in water, when crushed they sink much more slowly, and this exactly in proportion as they are more finely divided; thus, while the stones in a river will sink even when the current is swift, the coarse sand will be carried along and not sink unless the current is slow; while the very finest sand, notwithstanding it consists of the very same material as the stones, will not be deposited at all except where the water is at perfect rest, lienee the coarseness or fineness of the gravel in a river bottom depends on the speed of the current, .The most striking illustration of this property is found in the process of elutriation, practiced by chemists. It consists in grinding insoluble products with a little water to paste, and then suddenly diffusing#fce paste through a large quantity of in a deep vessel, from which, after ‘the subsidence of the coarser portion, which at once takes place, the supernatant liquid is poured into another vessel and allowed to deposit the next fine parts held in suspension. After a time, say fifteen or twenty minutes, it is again decanted and the apparently clear water left to settle for several days, when a small quantity of the very finest impalpable, powder is obtained. In the preparation of emery and other polishing powders of numerous grades of fineness, several vessels are employed; and the muddy liquid, first left to settle a short time, is poured in the second, left to settle a little longer, then poured iu the third, and so on. The powder of this hard substance last deposited is in so minute a state of division as to possess very great value as a polishing agent. Adhesion also exists between gases aud the surfaces of liquids or solids, and is the origin of many phenomena, the sole cause" of which must be looked for in this adhesion. If, for instance, there were no adhesion between the air and the surface of water, there vyoujd be no friction between them; and the wind would move freely over the surface of the ocean, and. would be unable to raise waves. The proof of this is that if we cover the surface of water with a film of a lighter liquid, like oil, having less adhesion to air, thus having friction less than that of wafer with air, the winds will glide over it without raising waves ; lieHce the wellknown quieting influence of oil on the surface of water agitated by the boisterous winds; and use of this property has occasionally been made with good effect when oil was ou hand. It is the same adhesion oi air to solids which causes the dust to be raised by wind, notwithstanding that the particles of dust are much heavier than the air.

But the most important example of this force of surface adhesion is the power of the air to hold °up fine particles of water in the form of clouds. To explain this apparently wonderful support of water in the atmosphere, so great a man as De Saussure had recourse to the absurd hypothesis that the water particles of which clouds and logs consist were small, hollow, vesicular spheres, like microscopic soap-bubbles with a vacuum inside, and therefore specifically lighter than the air. And microscopists even went so far as to investigate the vapor of hot water, to see if the ascending globular particles were hollow inside. Some of them even asserted that they found this to be so; but every one experienced in microscopic observations knows that it is next to impossible to decide if a very transparent globular object is hollow or solid, especially if it moves iu the field of the instrument, as is the case with the of ascending vapors. In the light of our knowledge of adtiesion, such an hypothesis is utterly unnecessary and uncalled for. We know that the dust of heavy solids, even of the metals, is carried by the air, as is proved by the microscopic observations of the dust collected from the roofs of the houses in any large city; why, then, cannot dust of water be carried upward and remain suspended ? If anyone doubt the existence of such ti-ater dust, let him observe the spray of the Falls of Niagara, or other large falls, and see liow it ascends. It is nothing but water ground to dust by the tremendous fall; aud when the atmosphere is not dry enough to absorb it and make it disappear it will rise to elevations of hundreds anti ihmtsands of feet, and-form real clouds, which will float away with the others. The size of these particles determines the height to which they will ascend; the finer will form the upper clouds, tlif coarser the low, floating fogs. Dr. Angus Smith recently recorded a fog which he observed in Iceland, of which the particles were larger than he ever saw before. It rolled low over the ground like a dust, and microscopic observation convinced him that the particles were not hollow but solid, and he found the diameter to be 1-400 part of an inch He algo refers in his account to the absurdity of the vacuum hollow-sphere theory, which only shows that the greatest inventor is liable to invent erroneous theories. — Scientific American. *«■ 1 '!\ 4 " A shopkeeper purchased of an Irish woman a quantity of butter, the lumps of which, intended "for pounds, he weighed in the balance and found wanting. “ Sure, it’s your own fault if they are light,” said Biddy, in reply to the complaints of the buyer; “ it’s your own fault, sir, for wasn’t it with a pound of your own soap I bought here myself that I weighed them ?" The shopkeeper had nothing more to say no that subject. Texas farmers will plant double “the amount of small grain next year tL at they did last. .