FIG. 1.—TOTAL REFLECTION OF LIGHT IN GLASS
Take next the quality of brilliancy. This depends upon two things—first, the manner in which rays of light are affected when they enter or leave the stone, and, secondly, the manner in which this action can be intensified by the art of the lapidary.
When light passes from one transparent substance to another it is bent or refracted, as every one knows from the bent appearance of a stick plunged into water. Consider, now, a ray of light falling upon the surface of a transparent stone; a portion of the light is reflected, but a portion enters the stone. In passing from air into the stone it is refracted inward. When, on the other hand, it passes from a transparent stone into air, its course is reversed and the emerging ray is refracted outward or toward the surface. It is, however, with the emerging as with the entering light, the beam is subdivided, only a portion is refracted out, another portion of the light is reflected within the stone.
Consider next successive rays within a piece of glass or a stone which are about to emerge with different inclinations. (See Fig. 1.) As their course approaches more nearly to the surface, so will the emerging rays issue more nearly along the surface of the stone; but the obliquity of the emerging rays increases much more rapidly than that of the internal rays, until for one ray in the series the direction of the light (C in the figure) refracted out coincides with that surface. What, then, will happen to the light within the stone, which falls still more obliquely? It cannot be refracted out, and, as a fact, it is entirely reflected within the stone. Imagine, then, how much greater is the brilliancy of the beam of light, c, e, d, which is completely reflected, than that of the intermediate portion of the reflected light, a, b, c, which has lost a large part of its rays by refraction. The difference is easily seen by looking at a glass of water held above the head; the brilliant silvery appearance of the surface, when viewed obliquely, is due to total reflection. The light, c, d, e, is said to have been totally reflected; and half the angle between C and c is called the "angle of total reflection." This angle depends upon the refractive power of the stone. The angle of total reflection for diamond is about 25°; in no other stone is the corresponding angle less than 30°; for most of them it is much greater; while for heavy glass it is about 40°. Light striking the internal surface more obliquely is reflected without losing any of its rays by refraction.
FIG. 2.—TOTAL REFLECTION OF LIGHT WITHIN A BRILLIANT
It is very clear, then, that of the light traveling in directions within a diamond, a far larger proportion is internally reflected than is the case with any other stone. We shall see presently that it is this property which gives the diamond its consummate brilliancy.
Another effect produced by refraction is, as every one knows, the separation of ordinary light into rays of different colors—it is seen in any prism of glass. This property is known as the "dispersion" of light; and a stone which possesses great dispersion will exhibit a beautiful play of spectral colors—will exhibit a high degree of what is called fire. In this respect again the diamond is pre-eminent; its dispersion is nearly twice as great as that of other stones.
All these optical properties are beautifully shown by those unworked jewels of which the smooth facets have been produced by nature; I mean the crystals of the various minerals. The beauty of natural crystals of transparent minerals is largely due to the optical effects which I have just been describing.
The beautiful specimens of rock crystal, calc spar, topaz, emerald, and other stones which adorn mineral collections are sufficient evidence of these properties. But it is very certain that natural crystals, although they possess a beauty of form which is all their own, are not by a long way so brilliant as the faceted stones which are cut from them by the art of the lapidary; that a natural diamond is not so lustrous as a faceted brilliant.
In fact, many of the finest gem stones present a very mean and sordid aspect before they have passed through the hands of the lapidary; one has only to compare the dull and unattractive appearance of a parcel of rough rubies, sapphires or rough diamonds with the finished jewels displayed in the jewelers' windows to see how much these owe to the lapidary's art.
In recutting the Koh-i-noor it was thought advisable to spend £8,000 on the process and to reduce its weight from 186 to 106 carats. When the great Pitt diamond was cut, its weight was reduced from 410 carats to 137; and the fragments and dust removed were valued at £8,000; but the extent to which the stone was improved is indicated in the fact that having been purchased for £20,000, it was after cutting sold for £135,000.
To understand how the cutting of a precious stone adds to its brilliancy, we have only to trace the course of the rays within the stone, and consider how it can best be faceted in order that the light which enters in various directions on the upper side, or crown, may be reflected internally from facet to facet on the under side of the stone with as little loss as possible, and may be thrown out from the front of the stone. For this purpose the facets must be so arranged that as much of the light as possible within the crystal shall meet the facets at an inclination exceeding the angle of total reflection. A brilliant with its 58 facets is one of the forms which experience has shown to be best adapted for the purpose. How little of the light gets through a stone so faceted, and, therefore, how much of it is totally reflected internally, is easily shown by holding the stone in a strong beam of light; first so that the light is so reflected, and then so that the light shall, if possible, be transmitted. In the latter case, the stone merely throws a dark shadow, indicating that little light, if any, has passed through it.
A faceted stone is always cut from a single crystal, and not from an ordinary lump of the mineral, which is generally a mass of crystals. The chief reason why jewels are cut from natural crystals is that these, by virtue of their crystalline nature, are remarkably homogeneous, and therefore clear and limpid when free from cracks and flaws. A stone which is not homogeneous can never have the purity and limpid brilliancy of a single crystal, for at every point of contact of one part with another reflection takes place. Among minerals used as precious stones which are not crystals may be mentioned the opal. The opal probably owes its peculiar beauty to the very fact that it is filled with minute cracks or cavities, each of which contributes some tint of color by reason of its extreme thinness, just as the colors of the soap bubble are due to the thinness of its film.
Or take the agate. Here the stone consists of layers of different materials differently colored. Its beauty is of a different nature from that of clear crystals, which it can never rival in brilliancy. Stones like the agate are generally classed apart as semi-precious stones, and their interest depends upon beauty of structure or color, or possibly to a large extent upon their rarity. The turquois, for example, is a very rare stone, which is apparently absolutely uncrystallized, but possesses great beauty of color, and is therefore much prized. The same is true of carnelian. On the present occasion we are not concerned with those opaque or curiously structured minerals whose beauty resides almost solely in their color.
Those who have had no practical acquaintance with minerals have little idea how variable and accidental are their colors. They may scarcely realize that the ruby and the sapphire are the same mineral, and that this mineral also occurs, and is used in jewelry, absolutely colorless, when it is known as lux sapphire, green as the so-called Oriental emerald, and yellow as the so-called Oriental topaz; that topaz itself may be yellow, brown, blue, or colorless; that zircons range from colorless through almost all conceivable shades of brown and green, and that even diamond has been found green, red and blue.
When we come to consider the properties by which precious stones are recognized, I shall say little or nothing about color, for it is of little value as a criterion. There are, for example, certain red stones which the most skillful experts cannot by their color alone refer with certainty to ruby, garnet or spinel. It might be expected that a noteworthy difference in chemical composition would accompany this difference of color, or that the pigment could be ascertained by analysis. In reality this is scarcely ever the case. It is fairly certain that the emerald owes its color to the presence of chromium, but the variation in the analyses of precious stones cannot generally be attributed to anything indicated by the variation of color.
The chemical composition, though of great general importance in mineralogy, is of little practical value in the discrimination of precious stones, since it is usually impossible to sacrifice a sufficient quantity for chemical analysis. If we are dealing with a faceted stone, not even the smallest portion can be utilized, for fear of injuring it.
There is, however, one remarkable optical property, which is ultimately related to the chemical composition. As is well known, many substances possess the property of absorbing certain rays of light. When the solar spectrum produced by admitting ordinary daylight through a slit, and transmitting it through a prism, is passed through the glowing vapor of certain substances, particular rays of light are absorbed, and their absence from the emerging fight is manifested by corresponding dark bands in the spectrum. The instrument by which the observations are made is the spectroscope. It is well known to most people that the solar spectrumitself contains certain dark bands of this sort, which are produced by vapors that can be identified by the position of the bands in the spectrum; and thus it is possible to ascertain something regarding the chemical constitution of the sun and certain of the heavenly bodies. Now, a precisely similar effect is produced by certain elements if present in a mineral, by merely transmitting the light through a piece of it. Thus, transparent minerals which contain the rare element didymium betray the presence of that element as soon as they are viewed through a spectroscope by ordinary daylight; the spectrum is seen to be traversed by black bands in the green, which are quite characteristic.
Among gem stones there are two which possess this curious property. One is the variety of red garnet known as almandine, and the other is the jargoon. The almandine produces characteristic bands in the green and the jargoon in the red, green and blue portion of the spectrum. To see these remarkable absorption spectra, to which attention was first called, I think, by my friend, Prof. Church, it is not necessary to look through the stone, it is quite sufficient to place it in a strong light, and look at it through an ordinary pocket spectroscope; the light which enters the instrument consists largely of rays which have penetrated the stone, and been reflected from the facets at the back. These rays produce the absorption spectrum. In this way we are enabled to identify a jargoon or an almandine merely by looking at it. There is no test so simple or so easy of application. It is curious that the almandine, or iron aluminum garnet, is the only garnet which presents an absorptive spectrum, and it is not yet certain to what element the bands are due. In the case of jargoon, they are supposed to be caused by the presence of some uranium compound in the mineral. All the almandine garnets which I have examined, and nearly all the jargoons, show these characteristic absorption spectra.
FIG. 3. Graph of Specific gravity vs Refractive index of gems
By way of summary, I have thought it desirable to indicate the general characters of precious stones in a diagram, which exhibits some of their relationships and also some of their differences in a graphic manner.
Opal, which is a comparatively light mineral, has a low refractive power; zircon or jargoon is a heavy mineral, and has a high refractive power. Let now the refractive power of any mineral (as measured by its refractive index for yellow light) be represented by a corresponding length set off from left to right, and let its density (as measured by its specific gravity) be represented by a corresponding length measured downward. Fixing in this way a point corresponding to opal, and another representing the character of zircon, draw a straight line from the one to the other. It will then be found that the points which, by their position on the diagram, represent the specific gravity and refractive index of the various minerals will be very nearly upon this line; that is to say, as the refractive index of precious stones increases, so also does their density, and the two increase together in a remarkably regular manner.
It appears from this table that those minerals which, by their high refractive power, possess the greatest brilliancy, possess also the highest specific gravity or weightiness; that the precious stones are therefore all heavy minerals. There is also a rough general correspondence between these characters and the hardness of the stones; the brilliant heavy minerals are also generally speaking hard.
Two remarkable exceptions display themselves. Sphene lies far to the right of the position which it should occupy according to its specific gravity; it possesses an extraordinarily high refractive index, and is, therefore, an extremely brilliant gem stone. On the other hand, a glance at the scale of hardness shows that it is, unfortunately, one of the softest of the possible gem stones, and that in this respect it is not very well fitted for jewelry.
Diamond is still more remarkable; its refractive index places it at the extreme right of the diagram, with a refractive power, and therefore a brilliancy, greater than that of any other stone; at the same time its hardness exceeds that of any mineral, and this combination of qualities renders it the chief among gem stones, unequaled for brilliancy and durability, although not a heavy mineral. Moreover, in dispersion, and therefore in fire, it stands alone. Minerals which are heavier than zircon, such as the metallic sulphides and iron glance, are unsuitable for gem stones, since they are nearly opaque, but they follow the same law, and possess a refractive power still greater than that of zircon or even diamond.
There is one other stone which is exceptional, but in less degree and in the other direction, namely, topaz, whose refractive index is not 1.7, as it should be by its position on the line due to the specific gravity, but 1.62; the point corresponding to topaz must therefore be placed a short distance to the left of the line. It is curious that these three exceptional stones lie on the same horizonal line, having all the same specific gravity, 3.5.
In mentioning the specific gravity I have introduced a property which is not essential to win esteem for a precious stone, but one which is of great value in its identification.
We have next then to consider those properties by which precious stones may in practice be most readily recognized. The table shows very clearly that specific gravity is one such property. The meaning of specific gravity is easily explained. A piece of tourmaline of any size weighs three times as much as an equal volume of pure water at 4° C., the specific gravity of tourmaline is therefore said to be 3; a piece of almandine garnet of any size weighs four times as much as an equal volume of water under the same conditions, and the specific gravity of garnet is therefore 4.
Now any substance immersed in water loses in weight by an amount exactly equal to that of the water displaced. Hence, to ascertain the specific gravity it is only necessary to suspend the stone by a fine thread to the beam of a balance and weigh it first in air, and then immersed in water. The first weighing gives the weight of the stone itself, the difference between the first weighing and the second gives the weight of the displaced water; hence the specific gravity is found at once by dividing the weight of the stone by this difference. For very small stones, where the weights concerned are slight, it is necessary to use a refined chemical balance. But for ordinary stones a well made Westphal balance is sufficient.
The Westphal balance is constructed on the principle of the common steelyard. At one end of the beam is a counterweight, at the other end the stone is suspended; the beam is divided into ten equal parts. A weight can be suspended on the beam, and its action, of course, varies with its position on the beam; at the tenth division from the center it has a value ten times as great as at the first division.
The specific gravity is then found as follows: First, counterpoise the counterweight. Let this require a weight, A, on the right hand side of the beam. Next, find the weight necessary to restore equilibrium when the stone is suspended from the beam. Let this be B. Then A-B is the weight of the stone in air. Next raise the vessel of distilled water below the stone until it is immersed. If C be the weight now required to restore equilibrium, C-B is the loss of weight in water, and, finally, the specific gravity is (A-B)/(C-B).
This process is known as "hydrostatic weighing," and can be applied to any stone, except such as are very small. Great precautions must be taken, in order to determine the specific gravity with accuracy. Especially it is necessary to free the stone from all adhering bubbles of air. For this reason the process of hydrostatic weighing is a somewhat laborious one.
Now, in order to identify a mineral, it ought to be unnecessary to determine exactly the specific gravity, provided that means can be devised for showing that its specific gravity is the same as that of some known substance. For purposes of identification, a comparative method is often quite as efficacious, and much more easy than actual measurement. This may now be done by means of certain heavy liquids.
Wood floats in water because it is lighter than water; iron sinks because it is heavier; but a substance which possessed exactly the specific gravity of water would neither float nor sink, but would remain suspended in the water like a balloon in midair. Taken, then, a liquid which is heavy—the most convenient is methylene iodide, whose specific gravity is 3.3—a fragment of zircon will sink in this, and a fragment of tourmaline will float, but a fragment of the mineral augite, whose specific gravity is also 3.3, will remain exactly suspended.
This liquid, then, enables one to say with certainty whether a given stone has a specific gravity greater or less than 3.3; in the one case it will sink, in the other it will float.
But methylene iodide further possesses the valuable property of mixing easily with benzene, which is a very light liquid. Every drop of benzene added reduces the specific gravity of the mixture, which can thus easily be made to range between that of chrysolite and that of opal.
To identify any one of the stones which lie between those limits on the diagram, it is only necessary to drop it into a test tube or small vessel containing methylene iodide—the stone will float—benzene is added drop by drop, the mixture being kept well stirred until a point is reached at which the stone neither sinks nor floats. Then different fragments of mineral possessing specific gravities between 3.3 and 2.5 are taken in order of increasing density and dropped into the liquid; the stone under examination possesses a specific gravity between that of the last which floated and the first which sinks, and the limits may, if necessary, be further narrowed by comparing it with other mineral fragments of known density intermediate between those two. One great advantage of this method is that the size of the fragment does not affect the result; a minute fragment only just large enough to be visible is equally convenient; in fact, more convenient than a larger one.
If a stone in the rough is under examination, a minute chip can easily be taken from it, and used for the experiment in the most satisfactory manner. The method is, moreover, extremely sensitive; a mere drop of benzene added to a considerable volume of the liquid is sufficient to send to the bottom a stone which was previously floating.
So much for stones whose density is less than that of chrysolite. As regards the denser minerals, it was until a short time back impossible to test them by any such method; they all sank in the heaviest liquid available. But now, thanks to the fortunate discovery by Dr. Retgers of the remarkable properties of thallium silver nitrate, all the known gem stones may be distinguished by a similar process.
This salt, which may be prepared by fusing together in equal molecular proportions nitrate of silver and nitrate of thallium, possesses the remarkable property of fusing at a temperature far below that of either of its constituents, and well below that of boiling water, while at the same time the fused salt possesses a specific gravity greater than that of zircon. The salt fuses at 75° C. to a clear colorless liquid in which zircon just floats; it further possesses the useful property of being miscible in all proportions with water, so that the specific gravity can be reduced to any desired extent by adding water, just as that of methylene iodide, was reduced by adding benzene. The substance can be kept liquid by maintaining it at a temperature above 75° C., and this may easily be done by immersing the vessel in which it is contained in water heated to near the boiling point.
In these two liquids then we have the means of producing a liquid of any required density for the discrimination of gem stones, since we can obtain from one or the other a liquid in which any precious stone will be exactly suspended.
The nitrate might be used by itself to include the whole series, but it is more convenient to use the methylene iodide when possible, both because it can be employed at ordinary temperatures and because it is cheaper than the nitrate.
Both substances darken on exposure to light, and should be both kept and used in the dark as far as possible: they are easily freed from the liquid employed to dilute them. The benzene readily evaporates spontaneously from the methylene iodide, and the water can be driven off from the diluted thallium silver nitrate by boiling.
(To be continued.)
[1]Lecture delivered before the Society of Arts, from the Journal of the Society.
[1]Lecture delivered before the Society of Arts, from the Journal of the Society.
My experiments on the liquefaction of helium were carried out with a sample of that gas, sent to me by Prof. Ramsay from London, in a sealed glass tube holding about 140 c. cm. I take this opportunity of rendering him my most sincere thanks. In his letter Prof. Ramsay informed me that the gas had been obtained from the mineral clevite, and that it was quite free from nitrogen and other impurities, which could be removed by circulation over red hot magnesium, oxide of copper, soda lime, and pentoxide of phosphorus. The density of the gas was 2.133 and the ratio of its specific heats (Cp/Cv) 1.652, the latter figure indicating that the molecule of helium was monatomic, as had already been found to be the case with argon. Prof. Ramsay further informed me that the gas was only very slightly soluble in water, 100 c. cm. of water dissolving scarcely 0.7 c. cm. of helium.
From the results of my earlier experiments I had been led to expect that it would be only possible to liquefy helium at a very low temperature; the small values obtained for the density and solubility of the gas, together with the fact that its molecule is monatomic, indicating a very low boiling point. For this reason I did not consider it necessary to use liquid ethylene as a preliminary cooling agent, but proceeded directly to conduct my experiments at the lowest temperature that could be produced by means of liquid air. The apparatus employed in these investigations is figured in the accompanying diagram.
The helium was contained in the glass tube, c, of the Cailletet's apparatus, C. The tube, c, reached to the bottom of a glass vessel, a, which was intended to containthe liquid air. The vessel, a, was surrounded by three glass cylinders, b, b' and b", closed at the bottom and separated from one another. The outer vessel, b", was made just large enough to fit into the brass collar, o, which supported the lid, u, of the apparatus. The tube, a, fitted into an opening in the center of the lid; the tube, t, connected with an apparatus delivering liquid oxygen, passed through a hole on the right. The vessel, b, was also connected with a mercury manometer and air pump by means of a T tube, p, v, one arm of which passed through the third hole in the lid of the apparatus. The tube, a, was closed by a stopper, through which passed the tube, c, of the Cailletet's apparatus, a tube connected with the drying apparatus, u, u', and one limb of a T tube, by means of which the manometer and air pump could be put in connection with the interior of the vessel. The lower part of the whole apparatus was inclosed in a thick walled vessel, e, containing a layer of phosphorus pentoxide.
By turning the valve, k, the vessel, b, could be partially filled with liquid oxygen, which, under a pressure of 10 mm. of mercury, boiled at about -210° C. Almost immediately the gaseous air began to condense and collect in the tube, a; a supply of fresh air was constantly maintained through the drying tubes, u and u', which were filled with sulphuric acid and soda lime respectively. When the quantity of liquid air ceased to increase, the tap on the U tube, u, was closed, the T tube, p' v', was connected with the manometer and air pump, and the liquid air was made to boil under a pressure of 10 mm. of mercury. In order to protect the liquid air from its warmer surroundings, a very thin, double wall tube, f, reaching to the level of the liquid in the outer vessel, was placed inside the tube, a. When, as in some of my experiments, liquid oxygen was used in the inner vessel, this part of the apparatus was dispensed with.
Helium cooling apparatus
Using the apparatus I have just described, I carried out two series of experiments, in which liquid air and liquid oxygen were employed as cooling agents. The tube of the Cailletet's apparatus was thoroughly exhausted by means of a mercury pump, and then carefully filled with dry helium. In the first series of experiments the helium, confined under a pressure of 125 atmospheres, was cooled to the temperature of oxygen boiling, first under atmospheric pressure (-182.5°), and then under a pressure of 10 mm. of mercury (-210°). The helium did not condense under these conditions, and even when, as in subsequent experiments, I expanded the gas till the pressure fell to twenty atmospheres, and in some cases to one atmosphere, I could not detect the slightest indication that liquefaction had taken place. The first time that I compressed the gas I had, indeed, noticed that a small quantity of a white substance separated out and remained at the bottom of the tube when the pressure was released. Possibly this may have been due to the presence of a small trace of impurity in the helium, but it could not have constituted more than 1 per cent. of the total volume of the gas.
In the second series of experiments I employed liquid air, boiling under a pressure of 10 mm. of mercury. The helium was first confined under a pressure of 140 atmospheres, and then allowed to expand till the pressure fell to twenty atmospheres, or, in some cases, to one atmosphere. The results of these experiments were also negative, the gas remained perfectly clear during the expansion, and not the slightest trace of liquid could be detected. The boiling point of liquid air was taken, from my previous determination, to be -220° C. (Comptes Rendus, 1885, p. 238). This number cannot, however, be taken as a constant, as the liquid air, boiling under reduced pressure, becomes gradually poorer in nitrogen. Further, the quantity of nitrogen lost by the liquid air on partial evaporation varies not only with the rate of boiling, but even according to the manner in which it has been liquefied.
If air, under high pressure, be cooled first to the temperature of boiling ethylene, and then to -150° C., it liquefies, and, on reducing the pressure slowly, liquid air is obtained boiling under atmospheric pressure. During the process a considerable quantity of the liquid air evaporates, and the proportion of nitrogen to oxygen in the remaining liquid is less than in air liquefied under high pressure. If the liquid air obtained by this process be made to boil under a pressure of 10 mm. of mercury, the proportion of nitrogen in the mixture continues to decrease, but, on account of the large quantity of oxygen present, the liquid does not solidify, although its temperature is some six degrees below the freezing point of nitrogen. When, as in some of my former experiments, the air was liquefied under normal pressure by means of liquid oxygen boiling under a pressure of 10 mm. of mercury, the ratio of nitrogen to the oxygen in the liquid air was the same as in the gaseous air from which it had been produced. The liquid air, obtained by direct condensation at normal pressure, appeared to lose oxygen and nitrogen with about equal rapidity, and at the end of the experiment a considerable quantity of liquid nitrogen remained behind in the apparatus. On reducing the pressure to 10 mm. of mercury the nitrogen solidified. Prof. Dewar has stated that liquid air solidifies as such, the solid product containing a slightly smaller percentage of nitrogen than is present in the atmosphere. My experiments have proved this statement to be incorrect; liquid oxygen does not solidify even when boiling under a pressure of 2 mm. of mercury.
After carrying these experiments to a successful conclusion, I found that it was yet necessary to prove that, on reducing the vapor pressure of boiling oxygen, to a minimum, no corresponding fall of temperature takes place. The vessel, e, was partially filled with liquid oxygen, and, by means of a small siphon, a small quantity of the liquid was allowed to flow into the tube, a. The inner vessel, a, was then connected with the air pump and manometer, and the pressure was reduced to 2 mm. of mercury. The oxygen remained liquid and quite clear. In a second experiment the temperature of the liquid oxygen, boiling under 2 mm. of mercury pressure, was measured by means of a thermometer. The temperature indicated lay above -220° C., a temperature easily arrived at by means of liquid air. I, therefore, concluded that liquid air was a much more efficient cooling agent than liquid oxygen, and that it would be quite unnecessary to make further experiments on the liquefaction of helium.
In every single instance I have obtained negative results, and, as far as my experiments go, helium remains a permanent gas, and apparently much more difficult to liquefy than even hydrogen. The small quantity of the gas at my disposal, and, indeed, the extreme rarity of the minerals from which it is obtained, compelled me to carry out my investigation on a very small scale. Using a larger apparatus, and working at a much higher pressure, I could have submitted the gas to greater expansion. Further, I should have been able to measure the temperature of the gas at the moment of expansion by means of a platinum thermometer, as I did when working with hydrogen; but to make such experiments I should have required 10, if not 100, liters of the gas. As I was unable to determine the temperatures to which I cooled the gas, by any experimental means, I have been obliged to calculate them from Laplace's and Poisson's formula for the change of temperature in a gas during adiabatic expansion.
T/T1= (p/p1)k – 1/k.
Where:
T, p are the initial temperature and pressure of the gas.T1, p1are the final temperature and pressure of the gas.k is the ratio (cp/cv) which, for a monatomic gas, is 1.66.
T, p are the initial temperature and pressure of the gas.
T1, p1are the final temperature and pressure of the gas.
k is the ratio (cp/cv) which, for a monatomic gas, is 1.66.
In the first series of experiments the gas, under a pressure of 128 atmospheres, was cooled down to -210° C.
The results of these calculations tend to show that the boiling point of helium lies below -264° C., at least 20° lower than the value I have found for the boiling point of hydrogen. If the boiling point of a gas be taken as a simple function of its density, helium, which, according to Prof. Ramsay's determination, has a density of 2.133, more than double that of hydrogen, should liquefy at a much higher temperature. Both argon and helium have much lower boiling points than might be expected, judging from their densities. This anomalous condition may be accounted for by the fact that in each case the molecular structure is monatomic, as shown by the values obtained for the ratios of their specific heats.
The permanent character of helium might be taken advantage of in its application to the gas thermometer. The helium thermometer could be used to advantage in the determination of the critical temperature and boiling point of hydrogen. To determine whether the hydrogen thermometer is of any value at temperatures below -198° C. I carried out a series of experiments, in which I measured the temperature of liquid oxygen boiling under reduced pressure. I made use of the identical thermometer tube employed by T. Estreicher (Phil. Mag. [5] 40, 54, 1898) as a hydrogen thermometer for the same purpose, and applied the same corrections as were made in his experiments.
The results of these experiments prove that the coefficient of expansion of hydrogen does not change between these limits of temperature, and that the hydrogen thermometer is a perfectly trustworthy instrument even when employed to measure the very lowest temperatures.
I have already pointed out (Wied. Ann., Bd. xxxi, 869, 1887) that the gas thermometer can be used to measure temperatures which lie even below the critical point of the gas with which the instrument is filled. For instance, the critical temperature of hydrogen, which I have found to be -234.5° C. (Wied. Ann., 56, 133; Phil. Mag. [5] 40, 202, 1898) can be determined by means of a hydrogen thermometer. The helium thermometer could be used at much lower temperatures, and would probably give a more exact value for the boiling point of hydrogen than it is possible to obtain by means of a platinum thermometer.
[1]Translated from the original paper, by Prof. K. Olszewski, in the Bulletin de l'Academie des Sciences de Cracovie for June, 1896, "Ein Versuch, das Helium zu verflunigen," by Morris Travers, and published in Nature.
[1]Translated from the original paper, by Prof. K. Olszewski, in the Bulletin de l'Academie des Sciences de Cracovie for June, 1896, "Ein Versuch, das Helium zu verflunigen," by Morris Travers, and published in Nature.
The instinct of spiders in at once attacking a vital part of their antagonist—as in the case of a theridion butchering a cockroach by first binding its legs and then biting the neck—is most remarkable; but they do not always have it their own way. A certain species of mason wasp selects a certain spider as food for its larvæ, and, entombing fifteen or sixteen in a tunnel of mud, fastens them down in a paralyzed state as food for the prospective grubs.
Perhaps the most entertaining points in connection with spiders are their concentration of energy, their amazing rapidity of action, and their inscrutable methods of transition and flotation.
During the past autumn large numbers of these creatures appeared at intervals. Thus I observed a vast network of lines that seemed to have descended over the town of Whitstable, in Kent, and which were not visible the day before or the day after. Many were fifteen to twenty feet long; they stretched from house to lamppost, from tree to tree, from bush to bush; and within six or seven feet of the ground I counted, in a garden, twenty-four or more parallel strands. The rapidity with which spiders work may be gathered from the fact that, while moving about in my room, I found their lines strung from the very books I had, a moment before, been using.
Insect life, as might have been expected after so mild a winter and so dry a spring and summer, is (1896) intensely exuberant. The balance is preserved by a corresponding number of Arachnida. On May 25 and 26 the east wall of the vicarage of Burgh-by-sands was coated with a tissue of web so delicate that it required a very close scrutiny to detect it. I could find none of the spinners. Every square inch of the building appeared coated with filmy lines, crossing in places, but mostly horizontal, from north to south.
Walking by the edge of a wheatfield in Suffolk on May 14, I observed all over the path, which was cracked with the drought, dark objects flitting to and fro. They were spiders—mostly of the hunting order. Tens of thousands must have occupied a moderate space of the field, and the cracks in the parched soil afforded them a handy retreat.
In reference to the visitation of spiders at Whitstable during the autumn and winter of 1895-6, it is right to note that the people of that place regard them as a sign of an east wind. In this connection we can note the fact of the phenomenal clouds of flies occurring at times on the east coast of England; and it would be interesting if observers could ascertain whether spiders ever cross the Channel and accompany such visitations of insects.
The production of the flotation line, and its method of attachment, are the two points to which I ask the attention of observers.
Is it not evident that air (and probably at a high temperature) must be inclosed within the meshes of the substance forming the line when it passes from the spinnerets into the atmosphere? The creature with this substance within its body drops to the ground at once by force of gravitation; yet, when emitted, the very same substance lifts it into the air. It has been usual to explain the ascent by the kite principle, i.e., the mechanical force of the contiguous atmosphere. But air movements, especially on a small scale, are so capricious and uncontrollable that, without a directive force, the phenomena seem quite inexplicable.
Moreover, all my own observations lead me to accept the theory of a direct propelling force, and I can hardly accept the conclusions on this point of Mr. Blackwall, though he is an authority on the subject. The intense rapidity with which the initial movements are made cannot be reconciled with any theory of simple atmospheric convection; and illustrations such as the following go to prove that spiders possess the faculty of weighting or condensing the ends of their threads, and throwing them, within limited distances, to a point fixed upon.
I was writing, and had two sheets of quarto before me. Perceiving a small spider on the paper I rose and went to the window to observe it. To test its power of passing through the air, I held another sheet about a foot from that on which the creature was running. It ascended to the edge, and vanished; but in a moment I saw it landing upon the other sheet through midair in a horizontal direction, and picking up the thread as it advanced.
In this case there was no air movement to facilitate, nor any time to throw a line upward, which, indeed, would not have solved the difficulty. Propulsion appears the only explanation.
The next illustration is more marvelous, and seems to indicate that some species, at any rate, have the power of movement through the air in any direction at will.
Some years ago, at a dinner party in Kent, four candles being lighted on the table, I noticed a thread strung from the tip of one of the lighted candles close to the flame, and attached to another candle about a yard off; and all the four lights were connected in this way, and that by a web drawn quite tight. No little surprise was caused among the guests on finding that the diamond form of the web was complete.
No satisfactory explanation of this has been offered, and I can only suggest that the spinner was suspended at first by a vertical line from above, and thus swayed itself to and fro, from tip to tip of the candles. It was certain that the spider could not have ascended from the table; and it was equally certain that aerial flotation of the line from a fixed point was impossible, as it involved floating in four opposite directions. I have seen a creature of this or a nearly allied species moving laterally through the air of a room in this way.—Knowledge.
Austriais turning out a new variety of Mannlicher repeating rifle for its army, which is the lightest rifle in the world, weighing 3.3 kilogrammes, seven pounds and four ounces, instead of 4.4 kilogrammes, nine pounds eleven ounces, the weight of the old pattern. All the individual parts in the new rifle, including the locking box, the magazine and the barrel, are lighter than in the old. The bayonet and sheath are also made lighter.
A trolleyexpress car system is now in successful operation in Brooklyn, N.Y. The trolley system of Brooklyn is one of the most extensive in the world, and many of the outlying districts are now served with great dispatch. Parcels are collected by wagons, they are then brought to the cars, and, after being carried to the nearest express station to their destination, they are then transported again by wagons. On Sundays the cars are run to carry bicycles.
In Stanislauoil gas is being a good deal used for incandescent lighting, says the Gas World. The gas is used at a pressure of from 1.1 in. to 1.2 in. When 1.7 cubic feet per hour is used the Welsbach mantle gives 69½ candles at first, 65 candles after 120 hours, 48¼ candles after 500 hours. The fall in lighting power is comparatively slow with oil gas, and the mantles are not so much worn by lighting the gas, for the kind of oil gas is not as explosive as that of coal gas. The mantles are found to last from 400 to 600 hours.
During theconstruction of the Simplon tunnel every possible alleviation will be made for the workmen employed, says the Railway Review. On leaving the tunnel when they are hot and wet through they will go at once to the douche and bathrooms provided for their accommodation, where, after a refreshing shower bath, they will resume their dry clothes. The sheds from which the workmen leave the tunnel are to be covered in and closed at the sides so as to protect them from cold. Water will be taken at intervals to the workmen who may require it, either from the pipe which feeds the drills or from that which brings water for cooling. No provision has been made as regards workmen's lodgings, because it is supposed that they will easily find accommodation in the neighborhood. As it is believed that the temperature of the rock of the Simplon tunnel may reach a maximum of 104° F., costly measures will have to be taken to cool the air in many parts where the works are to be carried on.
"Recent Developments in Lighthouse Engineering"was the title of a paper read recently at the Institution of Civil Engineers, by Mr. N.G. Gedye, says the Colliery Guardian. The author pointed out the marked development which has of late years taken place in the direction of reducing the length of flash emitted by lighthouse apparatus to a minimum, and the consequent increase obtained in intensity. The apparatus now being erected at Cape Leeuwin, Western Australia, gives a flash of one-fifth of a second duration every five seconds. It is the most powerful oil light in the world, the flash being over 145,000 candle power emitted from a pair of dioptric lenses mounted on a mercury float revolving once every ten seconds. Each of the two lenses is 8 feet in diameter. The powers of these oil lights are far exceeded by electric lighthouse lights, there being several in France up to 23,000,000 candle power, while there has recently been established at Fire Island, at the entrance to New York Harbor, an electric light, of French design and construction, of 123,000,000 candle power; this is the most powerful lighthouse light in the world.
Discussing theuse of potassium cyanide for steel-hardening purposes, T.R. Almond, of Brooklyn, N.Y., suggests that this salt assists the hardening process because of its powerful deoxidizing properties, and also because it forms a liquid film on the surface of the steel, which causes a more perfect contact between the steel and the water, thereby permitting a more rapid abstraction of heat. The inevitable formation of a thin coat of oxide is unfavorable to the process of rapid cooling; and as rapid cooling seems to be the one thing necessary for success in hardness, any means used for the removal of a bad conductor of heat, like the black oxide, will be of advantage, and more especially if this means also results in the formation of a liquid film on the steel surface having the affinity for water which, it is well known, is peculiar to potassium cyanide. Mr. Almond recommends the removal of all scale or oxide from the surfaces of steel to be hardened, either by pickling or by the cyanide. Steel covered with a very thin film of oxide will take the heat less quickly when immersed in hot lead than if the steel be bright before being immersed. This being the case, it would seem to follow that, because of a film of oxide, heat will leave steel more slowly when being cooled by water.
The gigantic wheel, now being erected on the site of the old bowling green in a corner of the Winter Gardens, Blackpool, was commenced on December 1, 1895, says the Building News. The work of erecting the supports was not finished until the third week in March, and then the most difficult portion of the work, viz., that of hoisting the axle, was commenced. The axle, a steel forging weighing over 28 tons and measuring nearly 41 ft. long and 26 in. in diameter, was forged at the works of Messrs. W. Beardmore & Company, of Glasgow. The axle and bearings being fixed complete, the work of building the rims of the wheel will be pushed forward rapidly under the direction of Mr. Walter B. Basset, who also built the Earl's Court wheel. The carriages, thirty in number, and each capable of carrying forty persons, are rapidly approaching completion in the works of Messrs. Brown, Marshall & Company, of Birmingham. The driving engines and most of the intermediate gearing are already in position in the engine house. These engines will operate two steel wire ropes, one on either side of the rim of the wheel, and arrangements have been made and provided for in such gearing to enable the wheel to be turned at a quicker speed than that at Earl's Court. The Blackpool wheel will be able to carry more passengers per hour than its predecessor in London. The particulars of the great wheel are: Total height above sea level, 250 ft.; total diameter (across centers of pins), 200 ft.; total weight, 1,000 tons. The solid axle is of a diameter through the journals of 2 ft. 2 in., a diameter across the flanges of 5 ft. 3 in., length over all 41 ft., and weight 28 tons.
Portraitsof Morse and Fulton are printed on the reverse of the new two dollar silver certificate, affording a relief to the dreary monotony of ex-presidents, generals and statesmen.
A monsterelectric elevator is to be erected at Allegheny, Pa. It will be large enough to carry up several wagons at once. The new elevator will save a trip of a mile and a quarter.
An excursion trolleycar on the Milwaukee Street Railway has 700 incandescent lights. The car is 32 feet over all. The platforms are 5 foot. The floor of the car is carpeted and a few tables for refreshments are provided.
Amsterdamwill have next year an international exhibition of hotel arrangements and accommodations for travelers. Among the features of the exhibition will be an "electric restaurant," without waiters, in which visitors will be served automatically with a complete dinner on pressing an electric button.
Prof. Fleminghas shown by experiments that with a 2,000 volt alternating current with a water resistance, that the latter is quite non-inductive, and that the readings of the amperes may be taken, says the Electrical World, as a measurement of the voltage, and the product of the volts and amperes will represent correctly the power consumed.
Ourcontemporary, The Engineer, suggests doing away with windsails on board steamers entirely and substituting electric fans. In warships the fan ought to be placed where room can be found for it low down in the ship, far below the water line. An electrically driven horizontal fan, with its motor, can be got into the thickness of a deck with its beams, if needs be. This would clearly be better than depending on a flimsy construction, which would certainly be greatly damaged, if not entirely shot away, in action. If clear decks are wanted, the windsail is about as inconvenient as it is ugly, and that is saying a great deal.
SinceJanuary 1, last, a new and reduced telephone tariff has been in force in Switzerland, and from reports to hand it appears to have worked satisfactorily all round. The former charge per annum for a telephone, with an annual limit of 800 conversations, was 80 francs (£3 4s.) The new tariff now in force is 40 francs (£1 12s.) per annum, plus an additional charge of 5 centimes for each local connection. The charges for interurban connections, with a time limit of three minutes, are as follows: Up to a distance of thirty-one miles, 3 d.; up to sixty-two miles, 5 d.; and above sixty-two miles, 7½ d. The telephone system throughout Switzerland is owned by the government, and the service, says the Electrician, is first class in every respect.
"There arethree ways by which high temperature may be measured," says the Electrical Engineer, London. "The first uses an air thermometer of refractory material; the second depends on the change in the resistance of a platinum wire with change in temperature; and the third is based on the employment of a thermo couple of relatively infusible metals. According to Messrs. Holborn and W. Wein, in a paper published in Wiedemann's Annalen, the air thermometer method was valueless until recently, as suitable vessels could not be made. But now these are produced from refractory clays, and permit of measurements up to 1,500° C. (2,732° F.) The results are, however, vitiated by the effects of capillarity in the interior of the vessel. The resistance method has also its disadvantages. At high temperatures the resistance generally increases, but the temperature coefficient is irregular. The presence of free hydrogen also affects the resistance. The third or thermopile method is favored by the authors, who prefer a circuit of platinum and an alloy of platinum with ten per cent. of rhodium. Temperatures up to 1,600° C. (2,912° F.) can be measured by it, and it is remarkably constant under various conditions."
The London Electricianstates that at a special meeting of the South African Philosophical Society held on August 2, a lecture on the above subject was delivered by Mr. A.P. Trotter, Government Electrician and Inspector. Toward the end of the lecture the lecturer rang up the Capetown Telephone Exchange, and asked if any of the longer post office telegraph lines were clear. The Port Elizabeth line was then connected up, and by means of a Wheatstone bridge on the lecture table, the resistance of the line was measured. The lecturer then observed that, with the extremely sensitive instrument used in the Government Electrical Laboratory, it was not necessary to use ordinary electric batteries for signaling to such a distance as to Port Elizabeth. He disconnected the battery, and, plunging a steel knife and silver fork into an orange, sent signals by means of the feeble current thus generated. He then asked the front row of the audience to join hands, and, putting them in the circuit, sent signals through their bodies to Port Elizabeth and back by means of the orange cell. As a concluding experiment an omelette was made "under some disadvantages," and the cost of the electrical energy was stated to be only two cents.
"The questionof injury to the eyes from the electric light is being prominently discussed by scientists, oculists, and laymen throughout the country," says the American Journal of Photography. "While opinion widely differs as to the ultimate injury likely to result from the rapidly increasing use of electricity, the consensus of opinion is that light from uncovered or uncolored globes is working damage to eyesight of humanity. In a discussion of the subject a London electric light journal in defending its trade feels called upon to make some important admissions. It says: 'It is not customary to look at the sun, and not even the most enthusiastic electrician would suggest that naked arcs and incandescent filaments were objects to be gazed at without limit. But naked arc lights are not usually placed so as to come within the line of sight, and when they do so accidentally, whatever may result, the injury to the eye is quite perceptible. The filament of a glow lamp, on the other hand, is most likely to meet the eye, but a frosted bulb is an extremely simple and common way of entirely getting over that difficulty. The whole trouble can be easily remedied by the use of properly frosted or colored glass globes. In any case, however, the actual permanent injury to the eye by the glowing filament is no greater than that due to an ordinary gas flame.'"
Rubbertrees are reported found growing in Manatee County, Fla.
Japanproposes to build up her commercial navy by giving subsidies to ship builders on every ton above 1,000, and to ship owners for ships of 1,000 tons that can make ten knots an hour, the subsidy being increased for every 500 tons additional burden or every knot additional speed.
Rosa Bonheurbegan to work seriously at painting when she was about fifteen, and donned male attire so that she could go about without attracting attention. She wore it so naturally that no one ever suspected her of being a girl, and found it so comfortable that she has worn it ever since to work in. She and Mme. Dieulafoy, the wife of the explorer, are the only two women in France who are legally authorized to appear in public in men's clothes.
A devicefor permitting the unsophisticated guest to blow out the gas in his bedroom at the city hotel without inconvenience to himself or anybody else has been devised. The gas burner is made of a metal having great expansive and contractive properties. The gas is turned on in the regular way and a small screw is turned which admits a small flow of gas through the burner. The gas is lighted, and the heat expands the metal and automatically opens a valve permitting a full flow of gas. The gas can be turned off in the ordinary way, but if the gas is blown out the metal contracts, closing the valve, and all the gas that escapes is the very small quantity admitted by the screw valve.
A movementis on foot in Europe having for its object the securing of a complete census of the inhabitants of all the civilized countries of the world. With this end in view the several governments are to be approached with the request that they will endeavor to decide upon a mutual date for counting the people under their various jurisdictions. Heretofore the different countries have taken their census on different dates, and it has been impossible to obtain accurate statistics in regard to the world's population at any one particular period. It is suggested that the last year of the present century or the first year of the coming century would be the most appropriate date for obtaining statistics.
Of the376 suicides who ended their lives in New York last year, by far the greater number were divorced people, says the Medical Review. From a table prepared for the year 1895, it is shown that there were in Germany during that year 2,834 suicides of men either divorced or separated from their wives and 948 suicides of widowers, as against only 286 suicides of married men. It is also shown that 343 women separated from their husbands and 124 widows died by their own hands, in contrast with 61 married women and 87 unmarried. In Wurtemburg, to every million inhabitants, there are 1,540 lunatics among divorcés or women separated from their husbands and 338 among the widows, while there are only 224 among unmarried women. There are 1,484 lunatics among the men who are divorced or separated from their wives, 338 among the widowers, and only 236 among the bachelors.
The quarterlylist of American tin plate works, which was published in the Metal Worker a short time ago, shows that on July 1 there were thirty-six complete tin plate plants rolling their own black plates in actual operation in the United States and three in course of construction. The active plants possessed an aggregate of 179 tin mills, having an estimated yearly capacity of about 5,500,000 boxes of tin plates. In addition to these establishments there were thirty-one tin plate dipping works, without rolling mills, possessing an aggregate of 169 tinning sets. At the end of June the production of American tin plate is estimated to have been going on at the rate of over 4,000,000 boxes yearly. During the last quarter the New Castle Steel and Tin Plate Company, of New Castle, Pa., has completed large extensions to its works, making it an eighteen-mill plant. This gives the United States the largest and most complete tin plate works in the world. Its annual capacity is three-quarters of a million boxes.
The Moniteur Vinicolehas recently published a statement showing the wine production of the various countries of the world. From this statement it appears the yield in France amounted in the years 1895 and 1894 to 587,127,000 gallons and 859,162,000 gallons respectively; in Algeria to 83,549,000 and 80,124,000 gallons; Tunis, 3,956,000 and 3,936,000: Italy, 469,555,000 and 539,000,000; Spain 379,500,000 and 528,000,000; Portugal, 43,890,000 and 33,000,000; Azores, Canaries, and Madeira, 4,620,000 and 2,640,000; Austria, 66,000,000 and 88,000,000; Hungary, 63,030,000 and 46,103,000; and Germany, 80,190,000 and 110,000,000 gallons. In Turkey and Cyprus the production last year amounted to 52,800,000 gallons, and this compares with an average yield of 40,000,000 gallons. In Bulgaria the yield was 26,400,000 gallons; Servia, 17,600,000; Greece, 35,200,000; Roumania, 68,640,000; Switzerland, 27,500,000; the United States, 89,700,000; Mexico, 1,980,000; Argentine Republic, 29,700,000; Chile, 33,000,000, Brazil, 7,700,000; Cape of Good Hope, 2,420,000; Persia, 594,000; and Australia, 3,300,000 gallons.
TheHistorical Museum of Hesse Cassel, in Germany, says the Carpenter and Builder, contains a most remarkable collection of curiosities. It is in the form of a wooden library, composed of five hundred and forty volumes of folio and quarto sizes. The books are made of the different specimens of trees found in the famous park of Wilhelmshoehe. On the back of each of these singular books is pasted a large shield of red morocco, which bears the popular and scientific names of the tree and the family to which it belongs. Each label is inlaid with some of the bark of the tree, the moss and lichen, and a drop or two of the resin, if the tree produces it. The upper edge of the book shows the tree in its youth, cut from a horizontal section, with the sap in the center and the eccentric circles. The same method prevails with the lower edge, showing the changes that have taken place. The interior of the book, in the shape of a box, contains in manuscript the history of the tree, with numerous hints as to its treatment, capsules filled with seeds, buds, roots, leaves, and so on. The inner sides show the diverse transformations which take place from bloom to fruit.
Ambrosia Sirup.—
Amycose.—
Shake well, add soda water, and before serving add a small, thin slice of orange or pineapple. Serve with two straws in a 14 oz. tumbler.
Banana Sirup.—
Cut the fruit in slices and place them in a jar; sprinkle with sugar and cover the jar, which is then enveloped in straw and placed in cold water, and the latter is heated to the boiling point. The jar is then removed, allowed to cool, and the juice is poured into bottles.
Banana Cream.—
Shake well, add a few pieces of banana, and fill with soda water, using the fine stream, and serve in a 12 oz. tumbler with a spoon and straws.
Charlotte Russe.—
Shake and fill with soda water, using the fine stream. Serve in a 14 oz. tumbler with a spoon; it will have a head like a charlotte russe.
Chocolate Sirup.—
The chocolate and gelatin are dissolved in the water by boiling, and then the sugar is added and stirred until dissolved; or,
Heat together on hot water bath until the chocolate is melted, constantly stirring, and then add enough sirup to make 1 gallon. The sirup must be added in small portions at first, under constant stirring, and the result will be a superior sirup. Extract of vanilla may be added if it is desired to further improve the taste.
Clam Juice Shake.—
Add a pinch of salt and a little white pepper to each glass; shake well.
Coffee Sirup.—
Boil together, or pass through a suitable filter coffee pot, until one gallon of infusion is obtained; let it settle and add the sugar.
Egg Lemonade.—
Shake thoroughly. Draw a small quantity of soda water, fine stream only, and grate a little nutmeg on top.
Egg Phosphate.—
Draw into a thin 9 oz. tumbler, 2 oz. of Maltese (red) orange sirup, and add an egg, a few squirts of acid phosphate, and a small piece of ice; shake well, fill shaker with soda water—using the large stream only—and strain.
Orange Phosphate.—
—Montreal Pharmaceutical Journal.
American Metal Polishing Paste.—
Thoroughly mix the powders, then add the petrolin, etc.—Mag. Pharmacy.
Cement for Porcelain Letters.—
Mix, and add:
Make a paste, and use immediately.