Part 8

When water is heated, it remains immovable up to 100 degrees Centigrade, but then it is changed into vapor, or boils. This boiling is characterized by a peculiar feature, the temperature remains fixed at 100 degrees. It must be concluded, therefore, that the heat produced by the furnace and absorbed by the liquid is simply used in transforming the water into vapor. This fact was first discovered by the English philosopher, Black, who, not being able to explain the phenomenon, was content to demonstrate it and to speak of the heat as _latent_. He saw that it took five and a half times as long to change water into vapor as to heat it from zero to 100 degrees, and that consequently it must require five and a half times as much heat to work the change. Such is the law of boiling in the air, but let us see what it is in a vacuum.

It is clear that the pressure of the atmosphere on water is a hindrance to its expansion into vapor, and that this hindrance increases or diminishes with the pressure. In a vacuum, of course, the liquid is free from the pressure, so that boiling ought to take place at a lower temperature.

And experiment teaches that this is the case; water boils at a temperature of 82° or 65°, as the pressure is reduced to one half or a quarter of an atmosphere, it boils at zero, and even below, in a vacuum. And we reach this remarkable result, that the boiling and freezing points unite, and that ice is formed while vapor is set free. But, although the boiling is advanced, although it takes place at zero instead of at 100 degrees, although the vapor is cold instead of hot, and the change takes place in a vacuum instead of in the air, it is a general law that a large quantity of heat is used, becomes latent, and enters into the formation of vapor.

Supposing that we fill a bronze vessel of very thick sides with water, close it with a lid and fit into it a valve loaded with lead. Place this in a furnace whose temperature has been raised to, say, 230 degrees. The water will reach this temperature, and vapor will accumulate until it reaches a pressure equal to more than twenty-seven atmospheres.

Let us now open the valve, the vapor will escape, and as it carries with it the heat necessary for its expansion, the temperature of the water will gradually fall until it reaches 100 degrees, after which the boiling will continue slowly and regularly; thus the water has been cooled and is kept below the temperature of its surrounding wall because it must absorb the extra heat which is required to change it to vapor. This apparatus is called Papin’s digester.

There is a similar experiment, but performed in a vacuum at the ordinary temperature. Put some water into a closed decanter which is connected by a tube with an air pump. As soon as a vacuum is produced the water begins to boil and to freeze, for the vapor can only be formed by borrowing heat, and there is nothing to take it from but the water itself, which soon reaches zero and is frozen. This apparatus makes a very simple ice house, as useful as convenient, and it proves, first, that boiling takes place at the lowest temperatures providing the pressure is sufficiently diminished; secondly, that it is always accompanied by a loss of heat; and thirdly, that it lowers the temperature of the liquid below that of the surrounding envelope, and the more as the vacuum is more complete.

Just as opening the valve lets the vapor accumulated above the water in Papin’s digester escape, and causes a fall in the temperature, so, by opening the reservoirs in which one has confined a liquefied gas, one sees it fall back to the boiling point. For example, take the liquid obtained from the compression of sulphurous acid gas. As soon as the reservoir containing it is opened the liquid begins to boil, and a vapor is formed, it is the gas which re-forms. It absorbs the latent heat necessary, taking it from exterior objects by radiation from the liquid itself, from the vessel which holds it, and from the materials into which it has been placed. It cools these until the point at which sulphurous acid gas boils is reached, twelve degrees below zero; then the liquid remains balanced between the radiation which tends to heat it and vaporization, which cools it. The final result is that the temperature is lowered and remains fixed at twelve degrees below zero. This is not all: just as the boiling point of water is lowered below zero in a vacuum, in the same way that of sulphurous acid gas falls below twelve degrees. Bussy brought it down to sixty-eight, where it remained; not only water, but mercury may be frozen by this means.

Finally, the boiling of liquefied gases will freeze all neighboring substances, and the greatest cold which one could obtain is produced by their boiling in a vacuum. This property of sulphurous acid was discovered in a still greater degree in protoxide of nitrogen, which was changed into a liquid at a temperature of 0 degrees, and under a pressure of thirty atmospheres. If allowed to boil in a vacuum, a temperature of one hundred and ten degrees below zero was obtained. When science has sown trade reaps the harvest; since by allowing liquefied gases to boil, a temperature of one hundred and ten degrees below zero can be obtained, and since the vapors which they give off carry away an enormous amount of heat from the surrounding bodies, it is possible by means of this cold produced to freeze water, make cold drinks, solidify mercury, cool cellars, prevent food from decay, and to do many other things of similar nature. A new art became possible, that of making cold. To-day it is at the height of success. It is founded on this general principle: to liquefy the gas by means of pressure, taking care that it does not become heated, to introduce it into a freezer, where it is allowed to boil, and from which it absorbs the heat, to carry off the gas and introduce it again into the vessel, where it will by pressure be liquefied. The action is constant, the same gas acts indefinitely, and there is no other expense than that which is caused by running the pumps. In spite of these fine results and the extraordinary efforts put forth, the end was not attained. To be sure, some gases had yielded, but still there was a large number which resisted every effort. Was it necessary to give up the idea that the law of liquefaction of gases was general, or was it true that the exceptions were only the results of insufficient means? Faraday had never varied in his belief. One easily returns to the affections of his youth, and he believed that the time had come for making fresh efforts to prove his theory. After a rest of twenty-two years he determined to again take up the liquefaction of the rebellious gases. Means were not wanting. Thilorier had taught him how to solidify easily large masses of carbonic acid, and by mixing this solid with ether make a powerful freezing mixture; protoxide of nitrogen could be prepared with the same ease and abundance, and would boil regularly in a vacuum at a temperature of one hundred and twenty degrees below zero. Thus he was able to secure a degree of cold before unknown. For compression, he had a pump formed of two parts; one took the gas at its generation, and accumulated it in a reservoir under a pressure of fifteen atmospheres; the second part then received it; here it was subjected to a much greater pressure in a strong glass vessel which was plunged into carbonic acid or protoxide of nitrogen. Cold and pressure were thus combined. At that time nothing more could be done; fortunately this was enough to subdue most gases. Faraday had the satisfaction of liquefying nearly all gases, and of extending the law which he had announced, but still six, only six, refused to give up; among them were marsh gas, oxygen, nitrogen, and hydrogen. Science is a battle which must be continually renewed; the more the gases resisted, the greater the efforts made to conquer them. At first, new and energetic means of pressure were invented. Aimé, a professor in Algiers, secured a pressure of four hundred atmospheres, without result. M. Cailletet used a hydraulic press which exerted a force equal to seven hundred atmospheres, and afterward increased this to one thousand atmospheres, but still the gas resisted. At last it was found that pressure alone, however enormous it might be, could not liquefy the gases.

An English philosopher, called Andrews, put a new face on matters. He took carbonic acid gas at a temperature of about thirteen degrees and compressed it. The gas began to diminish in volume, and under a pressure of fifty atmospheres was suddenly liquefied, taking quickly a very great density, and falling to the bottom of the vessel, where it remained separated from its vapor by a surface as plainly marked as that which marks water and air. Andrews afterward tried the same experiment at a higher temperature, about twenty-one degrees. The same results were produced with but one difference: the liquefaction was less sudden. At a temperature of thirty-two degrees, instead of a separate and distinct liquid, undulating striæ appeared as the only signs of a change in condition which was not completed. Finally, at a temperature of above thirty-two degrees there was neither striæ nor liquefaction, but still it seemed as if a trace was preserved, for under certain pressure the density increased more quickly, and the volume diminished more rapidly. Thirty-two degrees is then the limit, a point between the degrees which permit and which prevent liquefaction. It is the _critical point_ which marks the separation between two very different conditions of a substance; below, we have a liquid; above, there is no change in appearance, but there enters a new condition, whose characteristics I will describe.

Generally a liquid is more dense than its vapor; for this reason it falls to the bottom, and the two are separated by a level surface. But supposing that we heat the vessel which contains them. The liquid expands little by little, until it equals, or even surpasses, the expansion of the gas, so that an equal volume weighs less and less. On the other hand, a continually increasing quantity of vapor is formed, accumulates at the top of the vessel, and becomes constantly heavier. Now, if the density of the vapor increases, or if that of the liquid diminishes under the right temperature, the two densities become equal. Then there is no longer a reason for the liquid falling, the vapor rising, or for a surface of separation. The two are mingled. Neither are they any longer distinguished by their different degrees of heat. When this critical point is reached, it is impossible to tell whether it is liquid or gas, since in either state it has the same density, the same heat, the same appearance, the same properties. This is a new state, a gaseous liquid state. The discovery of these properties showed why all the attempts to liquefy air had been useless. At an ordinary temperature the gas is in a gaseous liquid condition. Liquefaction can take place only when the liquid is separated from the vapor by its own greater density. The next step was therefore to lower the temperature below that of the critical point. This was understood and carried out about the same time by MM. Cailletet and Raoul Pictet. On the 2nd of December, 1877, M. Cailletet subjected oxygen in a glass tube to a pressure of three hundred atmospheres, and reduced its temperature to twenty-nine degrees below zero. The gas did not change in appearance, and was in all probability in the gaseous liquid condition. Nothing but more cold was wanting to liquefy it. The valve was turned, the gas escaped, and the temperature fell two hundred degrees, and the characteristic whitish mist was seen. Oxygen had been liquefied, perhaps solidified. The same result was reached with nitrogen, but nothing was done with hydrogen. While M. Cailletet performed this decisive experiment at Paris, M. Raoul Pictet achieved the same at Geneva. He had at his command all necessary materials, so that he subjected the oxygen to a pressure of three hundred and twenty atmospheres, and to a temperature of one hundred and forty degrees below zero. In this condition the gas was probably below the critical point, and when the reservoir was opened suddenly it began to boil and was thrown in every direction. M. Pictet believed that he liquefied, and even more, had solidified hydrogen, but he was doubtless mistaken. These results, however, were not satisfactory. M. Cailletet was preparing a new experiment when the Academy received the two telegrams given at the beginning of this article.

Wroblewski and his colleague, Olszewski, had boiled ethylene, a gas similar to that used for heating purposes, in a vacuum. The temperature fell to one hundred and fifty degrees below zero. It was the greatest degree of cold yet obtained, and was sufficient. The success was complete. The oxygen, previously compressed in a glass tube, became a fixed liquid. It was like the others, in the form of a colorless and transparent liquid, like water, but of a little less density. Its critical point was at one hundred and thirteen degrees below zero, forming itself below, never above, this temperature, and boiling rapidly at a temperature of one hundred and eighty-six degrees below zero. A few days after this the two Polish professors succeeded, in the same way, in liquefying nitrogen.

But if the question was settled for air was it also for nitrogen? M. Pictet, in his experiment, had used a weight of three hundred and twenty atmospheres, and cold of one hundred and forty degrees below zero. When he opened the reservoir a jet of gas, mingled with mist of steel gray color, burst forth. At the beginning of the experiment, solid fragments accompanied the jet; these fell to the floor with a sound like that of grains of lead. Naturally, M. Pictet thought that he had not only liquefied, but even solidified hydrogen, but unfortunately the experiment was not wholly satisfactory. For perfect success still more acute cold was needed, and here was oxygen and nitrogen to get it from. Nitrogen, the most refractory, was taken, and a degree of cold undreamed of before, attained; in the open air it reached one hundred and ninety-four degrees below zero, and in a vacuum two hundred and thirteen degrees below. These temperatures were so low that it was necessary to invent new methods for measuring them. A mercury thermometer was useless, because it froze at forty degrees, and alcohol because it became a solid at one hundred and thirty degrees. No liquid is able to resist such temperatures, so electric, or hydrogen thermometers, were employed.

Wroblewski and Olszewski have but lately achieved success. Having compressed the hydrogen in the above named manner, they froze it by means of nitrogen boiling in a vacuum. Still it did not liquefy. It was yet in a gaseous liquid state, but when the tube was opened then there appeared a transparent and colorless liquid. At last the question of the liquefaction of gases, which has been discussed so long, has been settled. When we think of the simplicity of these final experiments, it seems strange that the problem was so difficult to solve. The trouble lay in the fact that at the start there was everything to find out; there was the critical point and the means of freezing to discover. It was necessary to proceed by steps, using each gas for the reduction of the one more stubborn than itself. Really, as Biot says, nothing is so easy as what was discovered yesterday, nothing so difficult as what must be discovered to-morrow. It might be asked whether the result is worth the trouble necessary to collect these liquids. The answer must be left to the future. The chemist will take up this new law of gases, and art will adapt it to its purposes. For the present, all that it amounts to is that the natural philosopher has proven that all kinds of materials may exist in three conditions, and obey the same common laws.—_Abridged and Translated from “Révue des Deux Mondes” for “The Chautauquan.”_

AMERICAN DECORATIVE ART.

BY COLEMAN E. BISHOP.

Among the many so-called “booms” that followed the civil war, as the result of the wonderful intellectual, moral and material impulse that it gave the country, one of the most marked and promising of influence on the national character is the advancement in decorative art that this generation has seen and felt. Its presence and influence are observable in the general demand for more artistic interior finishing and furnishing: for better form and coloring in wall paper, frescoing, painting, floor-coverings, upholstery and drapery, and in that broader study of the harmonious wholes of which these are related parts.

It is not an art renaissance, so much as a new birth of popular art feeling; a creation, rather than a revival. Facts seem to indicate the beginning of the long-talked-of American school of art. It is a peculiar, and peculiarly-encouraging circumstance that this new development is native and popular instead of imported and select.

For, we may be very sure that any movement that is to abide and have much power over our people must be one that touches the average citizen. To reach him it must be American. It need not be divergent from, and it should not be antagonistic to established art principles; but, not the less, in its sympathies, subjects, and methods it must be national. An art that is to live with any people must be _of_ that people. With us this requirement of popularity is doubly strong, because we are so intensely national; because all institutions live and move and have their being in the commonalty, and because the citizen is the only source of living patronage of art here, where the state does not foster art as foreign states do. The artist must eat, and the people must feed him. Before they will pay for art, they must have sufficient culture to care for it dollars’ worth, and it must be of a nature to reach their sympathies. Even in monarchial England, Ruskin perceives the necessity for beginning at the bottom to upbuild national taste, and he addresses volumes of letters upon art “To the Workmen and Laborers of Great Britain” (see “Fors Clavigera”).

We have not much to hope for in the way of education of American taste from imported art, for this can never reach or touch the people. A few _dilettanti_ in our cities can do very little toward creating, or even influencing a national taste. They have no _rapport_ with true American culture; they offend national sensibilities by unreasoning rejection of everything undertaken here; and, above all, if they be brought to the test, it will be found that they generally have no fixed art principles back of their opinions and—prejudices. If the average American could not appreciate foreign works, he was not much helped to a better understanding of them by their admirers; and he came to think himself at least quite capable of correctly estimating devotees who could no more give good reasons for worshiping everything foreign than they could for scorning everything indigenous.

The most hopeful augury for this new interest is in the fact that it relates to that department of art which goes most directly into the lives and the homes of the people: and that it has been the first to take on marked American characteristics. Moreover, its commercial features will be potent influences for its spread and growth. It is capable of being at once the refiner, the educator and the almoner of thousands.

Confidence in the inherent genius of my countrymen, led me years ago to predict that all that was needed for the establishment of a school in any art was (1) the foundational training of mind or hand; (2) a belief that it can be done; (3) a market for it. The last most important of all, because demand inspires originality and creates supply, and because recompense is the great stimulus to inspiration. Genius in this age is pretty apt to have an eye to the main chance.

For all these reasons we are prepared for the conclusion that the impulse given to decorative art by the organizations known as the “Decorative Art Society,” and the “Associated Artists,” all of New York City, is the most valuable of anything that has been done since the nation’s new sense of the beautiful awoke. These are the parts of one movement possessing these characteristics:

It is distinctively American.

It has compelled recognition at home and abroad as well of its indigenous originality as of its artistic correctness and merit.

It has begun the production of exclusively American materials, designed and manufactured in this country, which are unequaled by anything foreign.

It is commercially successful.

By virtue of all these achievements, it is doing a missionary work for American art by encouraging similar efforts in other cities and other countries; by demonstrating that “good _can_ come out of Nazareth;” by putting in the way of thousands of talented women, suffering under repression and lack of opportunity or for inspiration of hope, the opening for culture and compensation combined.

It is to celebrate what has been accomplished, and haply, to suggest the opportunities open to others, that this narration is essayed.

The movement was, indeed, patriotic in its birth. It was inspired by the Centennial Exposition at Philadelphia. The specimens of decorative art from the South Kensington School in the English exhibit impressed Mrs. Thomas M. Wheeler, of New York, by their lack of originality and freedom, insomuch that she declared, “We can do better than that in this country without any school!” and she set about doing it in genuine American spirit. The first organization, The Decorative Art Society, which she instituted, was composed of several hundred ladies of New York. The plan was national, philanthropic and commercial—to serve art, help women, beat the British, and make money. Ladies in a large number of cities were influenced by correspondence and other efforts to form auxiliary societies. The seed of the new art interest thus widely sown is still bearing crops.

From this nucleus there were before long offshoots in two directions—in a higher and in a more rudimentary line. The Woman’s Exchange was organized to provide a market for the large surplus of handiwork of all kinds that was pressed upon the society; and a less numerous, more compact organization was originated to attempt a higher development of the work—this being called the Associated Artists. Thus they had three efficient agencies occupying ground in this order, artistically considered—The Woman’s Exchange, The Decorative Art Society, The Associated Artists. Each of these is still doing its appointed work, but our present purpose has to do only with the most advanced—The Associated Artists.

It should be said, however, of the Woman’s Exchange, that it has spread the most widely; because it deals with the simple forms of ornamentation which require but little training, but it produces articles that are salable. Thus it has become a bread-and-butter enterprise to a large mass of women. Not only do all of our leading cities now boast of Exchanges, but Princess Louise, after her first visit to this country, caused one to be formed in Canada. This “Yankee notion” has also been transplanted to Germany and Sweden.