There have been few who have contributed more to the general stock of knowledge daring the past year than Charles Tomlinson, F. R. S., F. C. S. Especially valuable is his theory of boiling as applied to the useful arts, of which we can give only a brief and cursory review. We will, however, endeavor to give our readers some of the, most prominent points and practical conclusions. According to this theory, a boiling liquid is a supersaturated solution of its own vapor. This is proved by holding a nucleus in any part of the liquid. It will instantly become covered with steam bubbles. But what is a nucleus ? It is a promoter of vaporization, which acts by virtue of its stronger adhesion for the vapor of the solution than the liquid from which it is produced. Among the most common and well-known nuclei are the soap used by distillers, butter used by the sugar refiners, bits of cedar used in Dr. Bostock's experiments, the brass wire used by Oersted, the pointed or rough bits of platinum used in chemical experiments and operations, etc. Mr. Tomlinson has shown that all these nuclei are imperfect, that if they act well at first, they are likely to become inert during a single operation, and, therefore, unreliable, and, as the result of his researches, he has discovered nuclei which will not only greatly facilitate the escape of vapor from boiling solutions, but which, acting upon an entirely different principle from the ones enumerated, and others similar to them, may be relied upon as permanent and uniform in their action : these will be named further on. Mr. Tomlinson says " all the substances which have hitherto been used empirically, because the principle which led to their adoption was not known, must be renewed at each operation, and as they are liable to cease their action before any operation is completed, they are liable to objection." They will cease to act as nuclei whenever they become chemically clean. In Mr. Tomlinson's paper upon this subject, read before the Society of Arts, he remarks: " It has been recommended to use sharp-pointed or roughened bodies, under the impression that steam is given off with greater facility from the points or the teeth. This is a mistake. Make these rough or sharp-pointed bodies clean, and they cease to act. Sharp, angular fragments of glass, washed in sulphuric acid and rinsed, no longer act as nuclei. A rat's-tail file passed through the flame of a spirit-lamp also becomes denucleized. A body such as a file is apt to collect between its teeth the greasy kind of matter that acts so well as a nucleus; and this has led to an idea in favor of rough bodies. The air is not a nucleus. When Dr. Bostock found his thermometer cease to act, and by taking it out of the liquid and waving it in the air it liberated vapor when restored to the liquid, the thermometer had caught from the air some unclean particles of dust, which acted for a moment as nuclei, until, by the action of the ether, they became denucleized." Mr. Tomlinson states that he has performed a very large number of experiments on the action of nuclei on various liquids at or near the boiling point, and they all point to the same conclusion; namely, that the action of a nucleus is differential, there being a greater amount o' adhesion between the nucleus and the thing dissolved than between the nucleus and the liquid. In the great variety of cases the nucleus is contaminated with some kind of oily, fatty, or greasy matter, and this, having a less adhesion for the liquid part of a solution than for the gas, or the salt, or the vapor of such solution, there is, consequently, a separation of gas, or salt, or vapor. The nucleus may be a solid thrown into t e vessel, or the sides of the vessel may act as a nucleus, or 1 tty matter may be thrown in, in order to make the vessel unclean, as in the case of the distillers and the sugar boilers. But in all cases of solid or liquid nuclei, we may always observe this differential kind of action, on which, he contends, the action of nuclei depends. The following experiment illustrates this : Five ounces of distilled water in a clean flask boiled at 213g-J Fah. Some perfectly clean mercury was poured in, enough to form a ring at the bottom of the flask. The water rose to 214, with much bumping, steam forming under the mercury, and distending it into hemispheres, each of which burst with a kick. It would Have been dangerous to have entirely covered the bottom of the vessel with the metal, for, as it was, the bursts were of an explosive character. While this uneasy boiling was going on, a very little dirty mercury was added to the flask, and, although the mercury was not more than one sixth of that previously added, the effect was remarkable. Instead of the uneasy kicking, j erking bursts, the boiling became brisk, easy, and soft, rapid volleys of steam-balls being given off by the metal, breaking up the mass of water, while the temperature remained steady at 212-sV- Further experiments will be alluded to in a future article, showing the reasons for selecting charcoal, coke, pumice-stone, and especially cocoa-nut' shell charcoal as the best known nuclei. Our readers engaged in dyeing, distilling, etc., will not fail to see the importance of this subj ect, as well as its possible application to saving of fuel in steam boilers, since whatever tends to lessen the adhesion of steam to the water contained in boilers, helps to economize fuel. The experiments we shall give in our next bear strikingly upon this point.
This article was originally published with the title "The Theory of Boiling—Tomlinson's Experiments and Conclusions" in Scientific American 21, 7, 106 (August 1869)