Water, when not in contact with anything, or when the force of adhesion is not called into action, generally may be said to assume the spheroidal state. This means that it . gathers itself together into a mass approximating more or less closely to the shape of a sphere. In the experiments with lycopodium, illustrated in our last issue, an instance of this was shown where solid globules of water rolled about freely upon a surface strewn with the substance in question. and preserved a sha.pe approximating to that of a sphere. These globules were in the spheroidal state, strictly speaking, but not so in the usual..application of -the term. It is commonly restricted to those cases in which a high temperature in the immediate vicinity of a mass of water is the proximate cause of its assuming this form. Every one has noticed that when drops of water fall on a hot range they do not spread out and evaporate, but, instead, form little balls and roll about on the hot metal until they disappear or roll off. The hotter the range, the more perfect is this effect. The experiment illustrated in the cut is the development of this phenomenon. A cup of bright metal, preferably of considerable thickness, is to be provided. This is most readily made THE SPHEROIDAL STATE OF WATER. out'of a silver coin, a quarter ortilalf dollar or a silver or trade dollar. The coin is placed over a hole, bored through a solid piece of wood, the hole being of nearly its own diameter. A” piece of hard wood,' cylindrical, with rounded end, is held with its rounded end upon the coin and driven down by several hard blows with a hammer. This hollows or cups the coin. If a silver dollar is used, it should be hammered until a cup nearly a. quarter of an inch deep is formed. A quarter dollar will answer if an eighth of an inch in depth. A support has now to be provided, and this is readily made out of wire. In the cut a helix of somewhat heavy wire acts as standard. For heat, an alcohol lamp may be used, and it is for such that the spiral support is especially adapted. But there is no necessity for an alcohol flame. A common gas flame will do perfectly. In this case the cup can be held in a cleft piece of wood. which will last some time before it is completely destroyed by the heat. The arrangement shown is very neat. The spiral is made of such size as to fit snugly around the neck of the lamp, and is open enough not to seriously interfere with the flame. When all has been thus arranged, the lamp is lighted. After a few minutes' burning the wire will frequently begin to show a red heat in its upper coil. But before this occurs the cup may be considered ready. A little water must be poured into it, a teaspoon being a convenient implement for this purpose. Instead of at once beginning to boil, as might have been expected, the fluid collects into an»oblate spheroid, and, rolling about from side to side, lies upon the hot surface without a sign of boiling. As long as the lamp is lighted this continues, except that the globule grows smaller and smaller, and after a considerable interval disappears. However familiar with the phenomenon, it is difficult to avoid the impression that the lamp is at fault, and that the coin is not hot enough to evaporate the water faster. But this is corrected by observing the anomalous form that the water assumes. and by the second phase of the experiment, that shows itself when the lamp is extinguished. The cup is to be made quite hot, and a large globule of water introduced, and the lamp extinguished. For some time nothing Flew is seen. The globule rolls about restlessly from side to side as before, until the heat falls sufficiently, when it suddenly loses its shape or collapses, fills the cup, and bursts into violent ebullition. If all is rightly proportioned, it will boil away completely, leaving the cup dry. In other words, the cup will not boil water until it becomes cool. The explanation is not so simple as it was formerly considered. It was in the older textbooks asserted that. the water rested on a cushion of steam, and so did not come in contact with the metal. This is measurably true, but the present theory is a modification of this, and asserts that it rests on a"Crookes' layer” of steam—a layer whose molecules beat .back and forth from metal to water, and so prevent, them from touching each other. It is known that they do not touch, as light can be seen under the globule when a flat plate is used in place of a cup. But if a mere steam cushion were the separating agent, it. would not be clear why it is- not squeezed out, requiring more and more steam to replace it, so as to exact a most rapid evaporation of the ,drpp, instead of the slow one that actually takes place. The Crookes' ! layer, with the disposition of the component molecules to vibrate or oscillate in straight lines, does away with much of the difficulty. The peculiar condition of water has often been invoked to explain boiler explosions. The assumption was, that in such cases. the water by excessive heat was kept from contact with some of the plates until the heat fell enough for contact to- be established, when the rapid evolution of more steam was supposed to effect the explosion. If, however, the relative weight of a boiler and the water contained are considered, as well as the high specific heat of water and the low specific heat of iron, the explanationwill appear a very poor one. Many other substances can be brought into this state, water being by no means the only one. Even solids rapidly subliming may form and rest upon a similar protective Crookes' layer. Thus solidi fled, carbonic acid . gas may be held in the hand or in the mouth without injury, because there is - no contact. If by pressure such contact is established; a severe “ burn” is produced by the intense cold. The solid is continually evolving carbonic acid gas, that maintains a Crookes' layer and prevents it from touching the skin. By use of a powerful lamp and larger cup, considerable amounts.of water - may be thus treated, and the . .experiment performed with increased- effect.. .In !luch cases, a very peculiar phase is the increasing violence of the final ebullition. If the cup is of heavy metal, the boiling that begins slowly grows more and more violent, until the water is exhausted, or nearly so, producing a regularly increasing or crescendo sound. The general proportions given by the coin cup described may be followed in making larger ones, and copper may be used instead of silver, with good results. Notice to Subscribers. This issue closes another volume of the Scientific American and Scientific American Supplem ent, and with it a number of semi-annual subscriptions expire. The publishers have no apprehension but that every one whose name is on the subscription list. will continue the paper, and the object of this notice is to suggest to present subscribers if they cannot induce some of their acquaintances to also become subscribers to one or both editions of the paper. 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The safest way to remit is by check, postal order, express order, or registered letter, made payable to the order of Munn&Co., and address all letters to 361 Broadway, New York. , . For a Rust Joint. For making a rust joint that will bear heat, cold, and rough usage, the • following formula has been highly recommended : Ten parts iron filings, three parts chloride of lime, and enough water to make into paste. Put the mixture in between the pieces to be joined and bolt them together, leaving until dry. After twelve hours the cement has been known to break off the .solid iron.
This article was originally published with the title "The Spheroidal State of Water"