Chapter VIII: MISCELLANEOUS.--The Inventors' Institute.--Address of the (2)

The fact that C in this arrangement is in reality a planetary wheel, will be perceived by the aid of the diagram, Fig. 45. Let C D be two pieces rotating about fixed parallel axes, each having a groove in which slides freely one of the arms, A C, A D, which are rigidly secured to each other at right angles.

The point C of the upper arm can at the instant move only in the direction C A; and the point D of the lower arm only in the direction A D, at the same instant; the instantaneous axis is therefore at the intersection, K, of perpendiculars to A C and A D, at the points C and D. C A D K being then a rectangle, A K and C D will be two diameters of a circle whose center, O, bisects C D; and K will also be the point of contact between this circle and another whose center is A, and radius A K = C D. If then we extend the arms so as to form the cross, P K, M N, and suppose this to be carried by the outer circle, _f_, rolling upon the inner one, F, its motion will be the same as that determined by the pieces, C D; and such a cross is identical with that formed by the tongues on the coupling-piece, C, of Fig. 44.

A O is the virtual train-arm; let the center, A, of the cross move to the position B, then since the angles A O B at the center, and A C B in the circumference, stand on the same arc, A B, the former is double the latter, showing that the cross revolves twice round the center O during each rotation of C; and since A C B = A D B, C and D rotate with equal velocities, and these rotations and the revolution about O have the same direction. While revolving, the cross rotates about its traveling center, A, in the opposite direction, the contact between the two circles being internal, and at a rate equal to that of the rotations of C and D, because the velocities of the axial and the orbital motion are to each other as _f_ is to F, that is to say, as 1 is to 2. Since in the course of the revolution the points P and K must each coincide with C, and the points M and N with D, it follows that each tongue in Fig. 44 must slide in its groove a distance equal to twice that between the axes of the shafts.

Another example of a disguised planetary train is shown in Fig. 46. Let C be the center about which the train arm, T, revolves, and suppose it required that the distant shaft, B, carried by T, shall turn once backward for each forward revolution of the arm. E is a fixed eccentric of any convenient diameter, in the upper side of which is a pin, D. On the shaft, B, is keyed a crank, B G, equal in length to C D; and at any convenient point, H, on B C, or its prolongation, another crank, H F, equal also to C D, is provided with a bearing in the train-arm. The three crank pins, F, D, G, are connected by a rod, like the parallel rod of a locomotive; F D, D G, being respectively equal to H C, C B. Then, as the train-arm revolves, the three cranks must remain parallel to each other; but C D being fixed, the cranks, H F and B G, will remain always parallel to their original positions, thus receiving the required motion of circular translation.

The result then is the same as though the periphery of E were formed into a fixed spurwheel, A, and another, _a_, of the same size, secured on a shaft, B, the two being connected by the three equal wheels, L, M, N. It need hardly be stated that instead of the eccentric, E, a stationary crank similar and equal to B G may be used, should it be found better suited to the circumstances of the case.

It is possible also to apply the planetary principle to mechanism composed partially of racks; in fact, a rack is merely a wheel of prodigious size--the limiting case, just as a right line is a circle of infinite radius. A very neat application of this principle is found in Villa's Pantograph, of which a full description and illustration was given in SCIENTIFIC AMERICAN SUPPLEMENT, No. 424; the racks, moving side by side, are the sun-wheels, and the planet-wheels are the pinions, carried by the traveling socket, by which the motion of one rack is transmitted to the other.

Thus far attention has been called only to combinations of circular wheels. In these the velocity ratios are constant, if we except the cases in which two independent trains converge, the two sun-wheels, or one of them and the train-arm, being driven separately--and even in those, a variable motion of the ultimate follower is obtained only by varying the speed of one or both drivers. It is not, however, necessary to employ circular wheels exclusively or even at all; wheels of other forms are capable of acting together in the relation of sun and planet, and in this way a varying velocity ratio may be produced even with a fixed sun-wheel and a single driver. We have not found, in the works of any previous writer, any intimation that noncircular wheels have ever been thus combined; and we propose in the following article to illustrate some curious results which may be thus obtained.

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THE FALLACY OF THE PRESENT THEORY OF SOUND.

Dr. H.A. Mott recently delivered a lecture before the New York Academy of Sciences, in Columbia College, on the Fallacy of the Present Theory of Sound.

He commenced his lecture by stating that "the object of science was not to find out what we like or what we dislike; the object of science was truth." He then said that, as Galileo stated a hypothesis should be judged by the weight of facts and the force of mathematical deductions, he claimed the theory of sound should be so examined, and not allowed to exist as a true theory simply because it is sustained by a long line of scientific names; as too many theories had been overthrown to warrant the acceptance of any one authority unless they had been thoroughly tested. Dr. Mott stated that Dr. Wilford Hall was the first to attack the theory of sound and show its fallaciousness, and that many other scientists besides himself had agreed with Dr. Hall in his arguments and had advanced additional arguments and experiments to establish this fact. Dr. Mott first gave a very elaborate and still at the same time condensed statement of the current theory of sound as propounded by such men as Helmholtz, Tyndall, Lord Rayleigh, Mayer, Rood, Sir Wm. Thomson, and others, and closed this section of the paper with the remarks made by Tyndall: "Assuredly no question of science ever stood so much in need of revision as this of the transmission of sound through the atmosphere. Slowly but surely we mastered the question, and the further we advance, the more plainly it appeared that our reputed knowledge regarding it was erroneous from beginning to end."

Dr. Mott then took up the other side of the question, and treated the same under the following heads:

1. Agitation of the air. 2. Mobility of the atmosphere. 3. Resonance. 4. Heat and velocity of the supposed sound waves. 5. Decrease in loudness of sound. 6. The physical strength of the locust. 7. The barometric theory of Sir Wm. Thomson. 8. Elasticity and density of the air. 9. Interference and beats. 10. The membrana tympani and the corti arches.

Under the first head Dr. Mott stated that all experiments and photographs made to establish the existence of sound waves simply referred to the necessary agitation of the air accompanying any disturbance, such as would of necessity be produced by a vibrating body, and had nothing to do directly with sound. He stated that in the Edison telephone, sound was converted directly into electricity without vibrating any diaphragm at all, as attested to by Edison himself. Speaking of the mobility of the air, he said the particles were free to slip around and not practically be pushed at all, and that the greatest distance a steam whistle could affect the air would not exceed 30 feet, and the waves would not travel more than 4 or 5 feet a second, while sound travels 1,120 feet a second. Under heat and velocity of sound waves, Dr. Mott stated that Newton found by calculating the exact relative density and elasticity of air that sound should travel only 916 feet a second, while it was known to travel 1,120 feet a second.

Laplace, by a heat and cold theory, tried to account for the 174 feet, and supposed that in the condensed portion of a sound wave heat was generated, and in the rarefied portion cold was produced; the heat augmenting the elasticity and therefore the sound waves, and the cold produced neutralizing the heat, thus kept the atmosphere at a constant temperature. Dr. Mott stated that when Newton first pointed out this discrepancy of 174 feet, the theory should have been dropped at once, and later on he showed the consequences of Laplace's heat and cold theory.

The great argument of the evening, and the one to which he attached the most importance, was that all scientists have spoken of the swift movement of the tuning fork, while in fact it moved 25,000 times slower than the hour hand of a clock and 300,000,000 times slower than any clock pendulum ever constructed.

Since a pendulum cannot, according to the high authorities, produce sonorous air waves on account of its slow movement, Dr. Mott asks some one to enlighten him how a prong of a tuning fork going 300,000,000 times slower could be able to produce them. He then showed that there was not the slightest similarity between the theoretical sound waves and water waves, and still they are spoken of as "precisely similar" and "essentially identical," and "move in exactly the same way." Considerable merriment was occasioned when Dr. Mott showed what a locust stridulating in the air would be called upon to do if the present theory of sound were correct. He stated that a locust not weighing more than half a pennyweight, and that could not move an ounce weight, was supposed capable of setting 4 cubic miles of atmosphere into vibration, weighing 120,000,000 tons, so that it would be displaced 440 times in one second, and any portion of the air could bend the human tympanic membrane once in and once out 440 times in one second; and that 40,000,000 people, nearly the whole population of the United States, could have their 5,000 pounds of tympanic membrane thus shaken by an insect that could not move an ounce weight to save its life; and that the 231,222 pounds of tympanic membrane of the entire population of the earth, amounting to 1,350,000,000, who could conveniently stand in 11¼ square miles, would be affected the same way by 34 locusts stridulating in the air. According to the barometric theory of Sir William Thomson, he showed that a locust would have to add 60,000,000 pounds to the weight of the atmosphere.

Under elasticity and density he stated that elasticity was a mere property of a body, and could not add one grain of force to that exercised by the locust, so as to assist it in performing such wonderful feats. Under interference he showed that the law of interference is fallacious; that no such thing occurs; and that in the experiment with the siren to show such fact, the octave is produced which of necessity ought to be when the number of orifices are alternately doubled, and the same effect would be produced with one disk with double the number of holes. Under the last head of his paper Dr. Mott proved that the membrana tympani was not necessary for good hearing, that in fact when it was punctured, a deaf man could in many cases be made to hear, and in fact it improved the hearing in general; the only reason why the tympanic membrane was not punctured oftener was that dust, heat, and cold were apt to injure the middle ear.

In closing his paper Dr. Mott said that he would risk the fallacy of the current theory of sound on the argument advanced relating to the impossibility of the slow motion of a tuning fork to produce sonorous waves, and stated that he would retire if any one could show the fallacy of the argument; but if not, the wave theory must be abandoned as absurd and fallacious, as was the Ptolemaic system of astronomy, which was handed down from age to age until Copernicus and his aide de camp Galileo gave to the world a better system.

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THE ATTOCK BRIDGE.

We give illustrations from _Engineering_ of a bridge recently constructed across the Indus River at Attock, for the Punjaub Northern State Railway. This bridge, which was opened on May 24, 1883, was erected under the direction of Mr. F.L. O'Callaghan, engineer in chief, Mr. H. Johnson acting as executive engineer, and Messrs. R.W. Egerton and H. Savary as assistants.

The principal spans cover a length of about 1,150 feet. It will be seen from the diagram that there is a difference of nearly 100 feet in the levels of high and low water.

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THE ELASTICITY OF METALS.

M. Tresca has contributed to the _Comptes Rendus_ some observations on the effect of hammering, and the variation of the limit of elasticity of metals and materials used in the arts.

He says that hitherto, in considering the deformation of solids under strain, two distinct periods, relative to their mechanical properties, have alone been recognized. These periods are of course the elastic limit and the breaking point. In the course of M. Tresca's own experiments, however, he has found it necessary to consider, at the end of the period of alteration of elasticity, a third state, geometrically defined and describable as a period of fluidity, corresponding to the possibility of a continuous deformation under the constant action of the same strain. This particular condition is only realized with very malleable or plastic bodies; and it may even be regarded as characteristic of such bodies, since its absence is noticeable in all non-malleable or fragile bodies, which break without being deformed. It is already known that the period of altered elasticity for hard or tempered steel is much less than for iron. In 1871 the author showed that steel or iron rails that had acquired a permanent set were at the same time perfectly elastic up to the limit of the load which they had already borne. With certain bars the same result was renewed five times in succession; and thus their period of perfect elasticity could be successively extended, while the coefficient of elasticity did not appear to sustain any appreciable modification. This process of repeated straining, when there is an absence of a certain hammering effect, renders malleable bodies somewhat similar to those which are not malleable and brittle. There is an indication here of another argument against the testing of steam boilers by exaggerated pressures before use, which process has the effect of rendering the plates more brittle and liable to sudden rupture.

M. Tresca also protests against the elongation of metals under breaking strain tests being stated as a percentage of the length. The elongation is in all cases, chiefly local; and is therefore the same for a test piece 12 inches or 8 inches long, being confined to the immediate vicinity of the point of rupture. The indication of elasticity should rather be sought for in the reduction of the area of the bar at the point of rupture. This portion of the bar is otherwise remarkable for having lost its original condition. It is condensed in a remarkable manner, and has almost completely lost its malleability. The final rupture, therefore, is that of a brittle zone of the metal, of the same character that may be produced by hammering. If a test bar, strained almost to the verge of rupture, be annealed, it will stretch yet further before breaking; and, indeed, by successive annealings and stretchings, may be excessively modified in its proportions.

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THE HARRINGTON ROTARY ENGINE.

The chief characteristic or principle of this engine is the maintenance of an accurate steam and mechanical balance and the avoidance of cross pressure. The power is applied directly to the work, the only friction being that of the steel shaft in phosphor-bronze bearings. Referring to the cuts, Fig. 1 shows the engine and an electric dynamo on the same shaft, all connecting mechanism being done away with, and pounding obviated. There are but two parts to the engine (two disks which supply the place of all the ordinary mechanism), both of which are large, solid, and durable. These disks have a bearing surface of several inches on each other, preventing the passage of steam between them--a feature peculiar to this engine. Fig. 2 represents an end elevation partly in section, showing the piston, A, and the abutment disk, B, in the position assumed in the instant of taking steam through a port from the valve-chamber, E. Fig. 3 is a vertical section through the center of Fig. 2, showing the relations of the disks, C, and the abutment disks, B, and gear. The piston disks and gear are attached to the driving shaft, H, and the abutment disks and gear are attached to the shaft, K. These shafts, H and K, as above stated, run in taper phosphor-bronze bearings, which are adjustable for wear or other causes by the screw-caps, O. The whole mechanism is kept rigidly in place by the flanged hub, r, bolted securely to the cylinder head, F. These flanged heads project through the cylinder head, touching the piston disk, and thereby prevent any end motion of the shaft, H, or its attachments. The abutment disks and shaft are furnished with similar inwardly projecting flanged hubs, which are provided with a recess, I, Fig. 2, on their periphery, located radially between the shaft, K, and the clearance space, J. Into this recess steam is admitted--through an inlet in the cylinder head not shown in the cuts. By this means the shaft, K, is relieved of all side pressure. The exhaust-port, which is very large and relieves all back pressure, is shown at D. The pistons and disks are made to balance at the speed at which the engine is intended to run. The steam-valve, for which patent is pending, is new in principle. It has a uniform rotating motion, and, like the engine, is steam and mechanically balanced. The governor is located in the flywheel, and actuates the automatic cut-off, with which it is directly connected, without the intervention of an eccentric, in such a way as to vary the cut-off without changing the point of admission. By this means is secured uniformity of motion under variable loads with variable boiler pressure. It also secures the advantage resulting from high initial and low terminal pressure with small clearances and absence of compression, giving a large proportionate power and smooth action.

Expansion has been excellently provided for, the steam passing entirely around before entering the cylinder. These engines are mounted on a bed-plate which may be set on any floor without especial preparation therefor. The parts are all made interchangeable. A permanent indicator is provided which shows the exact point of cut-off. The steam-port is exceptionally large, being one-fourth of the piston area. Reciprocating motion is entirely done away with. The steam is worked at the greatest leverage of the crank through the entire stroke. Among the other chief advantages claimed for this engine are direct connection to the machinery without belts, etc., impossibility of getting out of line, uniform crank leverage, capacity for working equally well slow or fast, etc. It has but one valve, which is operated by gear from the shaft, as shown, traveling at one-half the velocity of the piston.

With this engine a speed of 5,000 revolutions per minute is easily attainable, while, as a matter of fact and curiosity, a speed of 8,000 revolutions per minute has been obtained. An engine of this class was run at the Illinois Inter-State Exposition at Chicago for six weeks at a uniform speed of 1,050 revolutions per minute, furnishing the power for twenty-three electric arc lights, with a steam pressure not exceeding fifty-five pounds per square inch, and cutting off at from one-tenth to one-sixth of the stroke. It was taking steam from a large main-pipe, so there was no opportunity for an exact test of the amount of fuel used, but from a careful mathematical calculation it must have been developing one horse-power from three pounds of coal.

The inventor claims that, as his engine works the steam expansively, even better results would have been obtained had the engine been furnished steam at 100 pounds per square inch.

The Harrington Rotary Engine Company, 123 Clinton Street, Chicago, are the owners and manufacturers.

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In a can of peas sold in Liverpool recently the public analyst found two grains of crystallized sulphate of copper, a quantity sufficient to injuriously affect human health. The defendant urged that the public insisted upon having green peas; and that artificial means had to be resorted to to secure the required color.

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TESTING CAR VARNISHES.

By D.D. ROBERTSON.

At the Master Car-Painters' Convention, D.D. Robertson, of the Michigan Central, read the following paper on the best method of testing varnishes to secure the most satisfactory results as to their durability, giving practical suggestions as to the time a car may safely remain in the service before being taken in for revarnishing:

The subject which the association has assigned to me for this convention has always been regarded as important. There is no branch of the business which gives the painter more anxiety than the varnishing department. It is more susceptible to an endless variety of difficulties, and therefore needs more close and careful attention, than all other branches put together, and even with all the research and practical experience which has been given to the subject we are yet far from coming to a definite conclusion as to the causes of many of the unfavorable results.

Beauty and durability are what we aim at in the paint shop, and from my experience in varnish work we may have beauty without durability, but we have rarely durability without beauty, so that the fewer defects of any kind in our work caused by inferior material, inferior workmanship, or any other cause, it is more likely to be durable, and ought, therefore, to possess beauty. There are certain qualifications absolutely necessary to durability in varnish. The material of which it is made must be of the proper kind, pure and unadulterated; the manipulation in manufacturing must be correct as to time, quantities, temperature, handling, etc., and age is also necessary. The want of durability arising from the quality of the materials, or from the manner of manufacturing, the painter has no control over; but let me say here, that frequently a first-class varnish has been used upon a car, and after being in service for a short time it deadens, checks, cracks, chips, or flakes, and therefore shows a very poor record. The varnish is condemned, when in reality, had the varnish been applied under different circumstances and over different work, the result would have been good and the durability satisfactory.

I am satisfied that in many cases first-class varnish has to bear the odium, when the root of the evil is to be found nearer the foundation. The leading varnish manufacturers of this country have expended large fortunes to secure the best skill and appliances, and, indeed, to do everything to bring their goods to perfection. Their standing and respectability put them beyond suspicion, and their reputation is of too much value for them knowingly to put into the hands of large consumers an inferior article; and even when we have just cause to complain of the varnish, we ought to be charitable enough to attribute the mistake to circumstances beyond their control (for every kettleful is subjected to such circumstances), and not to charge them with using cheap or inferior material for the sake of gain.

If the question which has been given me means to give some method of testing before using, I confess my inability to answer. For varnish to be pronounced "durable" must be composed of the materials to make it so, and to ascertain this, chemistry must be called in to test it. Comparatively few painters understand chemistry sufficiently to analyze, and if they did, and found the material all that is necessary, the manipulation may have been defective, so as to injure its wearing qualities, and therefore I cannot suggest any way of pronouncing varnish durable before using it.

As to the common custom of hanging out boards prepared and varnished to the exposure of the sun and weather for months does not seem to me to be the correct way of testing durability. It is true we may by this mode get some idea of wearing properties, but the most thorough and correct way is to put the varnish to the same exposure, the tear and wear, that it would have in the regular service on the road on which it is to run. Cars while running are exposed to circumstances which boards on the wall are not subjected to. The cars under my charge run through two different countries and three different States, and therefore subjected to such a variety of climate and soil that the testing by stationary boards would completely fail to give the correct result. For example: I have placed two sample boards, prepared and varnished, and exposed them to all kinds of weather and to the constant and steady rays of the sun for an equal length of time, and both gave favorable results; and I have also put the same varnishes on a car and found very different results. One of the varnishes having some properties adapted to resist the friction caused by cinders, sand, and dust, and consequently not so liable to cut the surface, and therefore much more durable.

The system which I adopted long ago, and to which I still adhere (not on account of "old fogyism," but for want of better), is as follows: I have two varnishes which I want to put into competition to test their relative merits. With varnish No. 1, I do the south half of the east end of the car and the east half of the south side of the car, the north half of the west end, and also the west end of the north side; this is also done with the same varnish. On the other half of the car varnish No. 2 is put.

Thus you will see it is so placed that, should the car be turned at any time, both varnishes on each side will have the same exposure and circumstances to contend with. This I regard as the best method to test the durability of varnish. And again let me say that it would be wrong for me to argue that because the varnish which I use gives me the best results, therefore I would regard it the best for all to use. This would be wrong, inasmuch as we have a diversity of climates between Maine and California, and between the extreme northern and southern States. The varnish which has failed to give me satisfaction may be most suitable for other parts of the Union.

As to the second part of my subject, "What length of time may a car safely remain in service before being taken in for revarnishing?" this must be regulated by the nature of the run and general treatment of the car while in service. Through cars are frequently continuously on the road, and little or no opportunity can be had to attend to them while in service. Such cars should be called in earlier than those which make shorter runs, and where ample time is allowed at both ends of the journey to be kept in order. And again, cars which are run nearest the engine cannot make so large a running record as those less exposed. Some roads, for a variety of reasons which might be given, can run cars for 14 months with less wear than others can run 12 months. So that I hold that the master painter on every road should keep a complete and correct record of his cars, and have an opportunity to examine these at intervals and report their condition, in order to have them called in before they are too far gone for revarnishing. If this system was more frequently adopted, the rolling stock of our roads would be more attractive, and the companies would be the gainers.

I cannot lay down a standard rule as to the exact time a car should remain in service before being called in for revarnishing, but I find as a general rule with the cars on the Michigan Central Railroad that they should not exceed 12 months' service, and new cars, or those painted from the foundation, should not be allowed to run over 10 months the first year. By thus allowing a shorter period the first year the car will look better and wear longer by this mode of treatment. Cars treated in this way can be kept running for six and seven years without repainting.

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THE FIXATION OF MAGNETIC PHANTOMS.

When we place a thin sheet of cardboard or glass upon a magnet and scatter iron filings over it, we observe the iron to take certain positions and trace certain lines which Faraday has styled lines of magnetic force, or, more simply, lines of force. The figure, as a whole, which is thus formed constitutes a magnetic phantom. The forms of the latter vary with that of the magnet, the relative positions of the magnet and plate, etc.

The whole space submitted to the influence of the magnet constitutes a _magnetic field_, which is characterized by the presence of these lines of force, and the study of which is of the most important character as regards electro-magnetic action and that of induction. In order to study these phantoms it is convenient to fix them so that they can be preserved, projected, or photographed. Fig. 1 shows how they may be fixed. To effect this, we cover the plate with a layer of mucilage of gum arabic, allow the latter to harden, and then place the plate over the magnet. Next, iron filings are scattered over the surface by means of a small sieve, and, when the curves are well developed,[1] the surface is moistened by the aid of an ordinary vaporizer. The layer of gum arabic thus becomes softened and holds the iron filings so that the particles cannot change position. When the gum has hardened again, the magnet is removed, and the phantom is fixed.

[Footnote 1: The curves are obtained by striking the plate lightly with a glass rod.]

We thus have a tangible representation of the magnetic field produced by the magnet in the plane of the glass plate or sheet of paper. The number of these lines, or their density, is at every point proportional to the intensity of the field, and the curves that are traced show their direction. To finish the definition of the field, it remains to determine the direction of these lines of force. Such direction is, by definition, and conventionally, that in which the north pole of a small magnetic needle, free to move in the field, would travel. It results from this definition that the lines of force issue from the north pole of a magnet and re-enter the south pole, since the north pole of a magnet repels the north pole of a needle, and _vice versa._

These considerations relative to the direction and intensity of the magnetic field are of the highest importance for the physical theory of magneto-electric machines.

The following is another method of fixing phantoms, as employed by Prof. Bailie, of the Industrial School of Physics and Chemistry of the City of Paris. He begins by forming the phantom, in the usual way, upon paper prepared with ferrocyanide, and exposes it to daylight for a sufficient length of time. The filings form a screen which is so much the more perfect in proportion as it is denser, and, after fixation, there is obtained a negative phantom, that is to say, one in which the parts where the field is densest have remained white.

The same processes of fixation apply equally well to galvanic phantoms, that is to say, to the galvanic fields produced by the passage of a current in a conductor, and which consists of analogous lines of force. The processes may be employed very efficaciously and with certainty of success.--_La Nature._

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A CHIPPENDALE SIDEBOARD.

Our illustration this week is of a unique and handsome piece of Chippendale work. The outline is elegant, and the scrollings delicate. The pedestals are peculiar in their form, the panels being carved in draperies, etc. In the frieze are two drawers, with grotesque heads forming the handles. The back is fitted with shaped glass and surmounted by an eagle. The whole forms a very characteristic piece of work of the period, having been made about 1760-1770. As our readers are aware, Thomas Chippendale published his book of designs in 1764, with the object of promoting good French design in this field of art. This piece of furniture was sold at auction lately for 85 guineas.--_Building News._

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LIQUEFACTION OF THE ELEMENTARY GASES.

By JULES JAMIN, of the Institute of France.

The earlier experiments of MM. Cailletet and Raoul Pictet in the liquefaction of gases, and the apparatus by means of which they performed the process, were described in the _Popular Science Monthly_, March and May, 1878. The experiments have since been continued and improved upon by MM. Cailletet and Pictet, and others, with more complete results than had been attained at the time the first reports were published, and with the elucidation of some novel properties of gases, and the disclosure of relations, previously not well understood, between the gaseous and the liquid condition. The experiments of Faraday, in the compression of gases by the combined agency of pressure and extreme cold, left six gases which still refused to enter into the liquid state. They were the two elements of the atmosphere (oxygen and nitrogen), nitric oxide, marsh-gas, carbonic oxide, and hydrogen. Many new experiments were tried before the principle that governs the change from the gaseous to the liquid, or from the liquid to the gaseous form was discovered. Aime sank manometers filled with air into the sea till the pressure upon them was equal to that of four hundred atmospheres; Berthelot, by the expansion of mercury in a thermometer tube, succeeded in exerting a pressure of seven hundred and eighty atmospheres upon oxygen. Both series of experiments were without result. M. Cailletet, having fruitlessly subjected air and hydrogen to a pressure of one thousand atmospheres, came to the conclusion that it was impossible to liquefy those gases at the ordinary temperature by pressure alone. Previously it had been thought that the obstacle to condensing gases by pressure alone lay in the difficulty of obtaining sufficient pressure, or in that of finding a vessel suitable for manipulation that would be capable of resisting it. M. Cailletet's thought led to the discovery of another fundamental property of gases.

The experiments of Despretz and Regnault had shown that the scope of Mariotte's law (that the volume of gases increases or diminishes inversely as the pressure upon them) was limited, and that its limits were different with different substances. Andrews confirmed the observations of these investigators, and extended them. Compressing carbonic acid at 13° C. (55° Fahr.), he found that the rate of diminution in volume increased more rapidly than Mariotte's law demanded, and at a progressive rate. At fifty atmospheres the gas all at once assumed the liquid form, became very dense, and fell to the bottom of the vessel, where it remained separated from its vapor by a clearly defined surface, like that which distinguishes water in the air. Experimenting in the same way with the gas at a higher temperature (21° C. or 70° Fahr.), he found that the same result was produced, but more slowly; and it seemed to be heralded in advance by a more rapid diminution in volume previous to the beginning of the change, which continued after the process had been accomplished; as if an anticipatory preparation for the liquid state were going on previous to the completion of the change. Performing the experiment again at 32° C. (90° Fahr.), the anticipatory preparation and the after-continuation of the contraction were more marked, and, instead of a separate and distinct liquid, wavy and mobile striæ were perceived on the sides of the vessel as the only signs of a change of state which had not yet been effected. At temperatures above 32° C. (90° Fahr.), there were neither striæ nor liquefaction, but there seemed to be a suggestion of them, for, under a particular degree of pressure, the density of the gas was augmented, and its volume diminished at an increasing rate. The temperature of 32° C. (90° Fahr.) is, then, a limit, marking a division between the temperatures which permit and those which prevent liquefaction; it is the critical point, at which is defined the separation, for carbonic acid, between two very distinct states of matter. Below this point, the particular matter may assume the aspect of a liquid; above it, the gas cannot change its appearance, but enters into the opposite constitution from that of a liquid.

Generally, a liquid has considerably greater density than its vapor. But, if a vessel containing both is heated, the liquid experiences a dilatation which is gradually augmented till it equals and even exceeds that of the gas; whence, of course, an equal volume of the liquid will weigh less and less. On the other hand, a constantly larger quantity of vapor is formed, which accumulates above the liquid and becomes heavier and heavier. Now if the density of the vapor increases, and that of the liquid diminishes, they will reach a point, under a suitable temperature, when they will be the same. There will then be no reason for the liquid to sink or the vapor to rise, or for the existence of any line of separation between them, and they will be mixed and confounded. They will no longer be distinguishable by their heat of constitution. It is true that, in passing into the state of a vapor, a liquid absorbs a great deal of latent heat, but that is employed in scattering the molecules and keeping them at a distance; and there will be none of it if the distance does not increase. We are then, at this stage of our experiments, in the presence of a critical point, at which we do not know whether the matter is liquid or gaseous; for, in either condition, it has the same density, the same heat of constitution, and the same properties. It is a new state, the gaso-liquid state. An experiment of Cagniard-Latour re-enforced this explanation of the phenomena. Heating ether in closed vessels to high temperatures, he brought it to a point where the liquid could be made wholly to disappear, or to be suddenly reformed on the slightest elevation or the slightest depression of temperature accordingly as it was raised just above or cooled to just below the critical point. The discovery of these properties suggested an explanation of the failure of previous attempts to liquefy air. Air at ordinary low temperatures is in the gaso-liquid condition, and its liquefaction is not possible except when a difference exists between the density of the vapor and that of the liquid greater than it is possible to produce under any conditions that can exist then. It was necessary to reduce the temperature to below the critical point; and it was by adopting this course that MM. Cailletet and Raoul Pictet achieved their success. The rapid escape of the compressed gas itself from a condition of great condensation at an extremely low temperature was employed as the agent for producing a greater degree of cold than it had been possible before to obtain. M. Cailletet used oxygen escaping at -29° C. from a pressure of three hundred atmospheres; M. Raoul Pictet, the same gas escaping at -140° from a pressure of three hundred and twenty atmospheres; and both obtained oxygen and nitrogen, and M. Pictet hydrogen, in what they thought was a liquid, and possibly even in a solid form.

Still, it could not be asserted that hydrogen and the elements of the air had been completely liquefied. These gases had not yet been seen collected in the static condition at the bottom of a tube and separated from their vapors by the clearly defined concave surface which is called a _meniscus._ The experiments had, however, proved that liquefaction is possible at a temperature of below -120° C. (-184° Fahr.). To make the process practicable, it was only necessary to find sufficiently powerful refrigerants; and these were looked for among gases that had proved more refractory than carbonic acid and protoxide of nitrogen. M. Cailletet selected ethylene, a hydrocarbon of the same composition as illuminating gas, which, when liquefied by the aid of carbonic acid and a pressure of thirty-six atmospheres, boils at -103° C. (-153° Fahr.). M. Wroblewski, of Cracow, who had witnessed some of M. Cailletet's experiments, and obtained his apparatus, and M. Olzewski, in association with him, also experimented with ethylene, and had the pleasure of recording their first complete success early in April, 1883. Causing liquid ethylene to boil in an air-pump vacuum at -103° C., they were able to produce a temperature of -150° C. (-238° Fahr.), the lowest that had ever been observed. Oxygen, having been previously compressed in a glass tube, became a permanent liquid, with a clearly defined meniscus. It presented itself, like the other liquefied gases, under the form of a transparent and colorless substance, resembling water, but a little less dense. Its critical point was marked at -113° C. (-171° Fahr.), below which the liquid could be formed, but never above it; while it boiled rapidly at -186° C. (-303° Fahr.). A few days afterward, the Polish professors obtained the liquefaction of nitrogen, a more refractory gas, under a pressure of thirty-six atmospheres, at -146° C. (-231° Fahr.). Long, difficult, and expensive operations were required to produce this result, for the extreme degree of cold it demanded had to be produced by boiling large quantities of ethylene in a vacuum. M. Cailletet devised a cheaper process, by employing another hydrocarbon that rises from the mud of marshes, and is called _formene_. It is less easily liquefied than ethylene, but for that very reason can be boiled in the air at a lower temperature, or at -160°C. (-256° Fahr.); and at this temperature nitrogen and oxygen can be liquefied in a bath of formene as readily as sulphurous acid in the common freezing mixture.

MM. Cailletet, Wroblewski, and Olzewski have continued their experiments in liquefaction, and acquired increased facility in the handling of liquid ethylene, formene, atmospheric air, oxygen, and nitrogen. M. Olzewski was able to report to the French Academy of Sciences, on the 21st of July, 1884, that by placing liquefied nitrogen in a vacuum he had succeeded in producing a temperature of -213°C. (-351° Fahr.), under which hydrogen was liquefied. Contrary to the suppositions founded on the metallic behavior of this element, that it would present the appearance of a molten metal, like mercury, the liquid had the mobile behavior and the transparency of the hydrocarbons.

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EXAMINATION OF FATS.

The methods employed up to the present in examination of fats, animal and vegetable, are mere reactions lacking general application; scattered throughout the literature, and doubtful with regard to reliability, they are of little or no value to the experimenter--an approximate quantitative examination even of a simple mixture being exceedingly difficult if not impossible, since the qualitative composition of fatty substances is the same, and the separation of the nearer components impracticable. The object of analysis consisted in estimating the accompanying impurities of fat, as, resin, albuminoids, and pigments. The nature of these substances depends on the mode of extraction and preservation of the fat, and are subject in the course of time to alteration. The only reaction based upon the chemical constitution of fat is produced by treatment of oleic or linoleic acid with nitrous acid, which therefore is of some value in the examination of drying oils. Of general application are the methods which correspond to the chemical constitution of fats, and thus determine the relative quantity of the components; advantage can then be derived from qualitative reactions, inasmuch as they further affirm the result of the quantitative test, or dispel any doubt with regard to the correctness of the result. The principal methods which comply with these demands have been carefully studied by Hueble for the purpose of discovering a process of general application; methods founded on the determination of density, freezing, and melting point were compared with those dependent on the solubility of fatty substances in glacial acetic acid or a mixture of alcohol and acetic acid; also the method of Hehner for testing of butter, the determination of glycerine and oleic acid, and at length the process of saponification. Nearly all fats contain members belonging to one of the three series of fatty acids, _e.g._, acids of the type of acetic acid (stearic and palmitic acids); such as are derivatives of acrylic acid (oleic and erucic acids); and such as are homologues of tetrolic acid (linoleic acid). It is likely that the relative quantity of each of these acids is variable, with regard to the same fat, within definite limits, and changes with the nature of the fatty substance. The groups of fatty acids are distinguished by a characteristic deportment toward halogens; while members of the first series are indifferent to haloids, those of the second and third class combine readily, without suffering substitution, with two respectively four atoms of a haloid. In view of this behavior the first series is termed saturated, the second and third that of unsaturated acids. Addition of halogen to one of the unsaturated acids yields on subsequent examination an invariable quantity of the former, representing two or four atoms, according to one or the other of unsaturated groups; and as the molecular weights of fatty acids are unequal, the percentage quantity of halogen will be found varying with regard to members belonging to the same series. The amount of iodine absorbed by some of the fatty acids is illustrated by the following items:

Hypogallic acid, C_{16}H_{30}O_{2}, combines with 100.00 grammes. iodine. Oleic acid, C_{18}H_{34}O_{2} " " 90.07 " " Erucic acid, C_{22}H_{42}O_{2} " " 75.15 " " Ricinoleic acid, C_{18}H_{34}O_{3} " " 85.24 " " Linoleic acid, C_{16}H_{28}O_{2} " " 201.59 " "

Of the halogens employed in the examination, iodine is preferable to either chlorine or bromine; it acts but slowly at ordinary, but energetically at elevated temperatures. The reagents are solution of mercury iodo-chloride prepared by dissolving of 25 grms. iodine, 500 c.c. alcohol of 95 per cent., and of 30 grms. mercury chloride in an equal measure of the same solvent; both liquids are filtered and united; a standard solution of sodium hyposulphite produced by digestion of 24 grms. of the dry salt with 1 liter water and titration with iodine solution; solution of potassium iodide of 1:10; chloroform, and finally a solution of starch. The above solution of mercury iodo-chloride acts on both free unsaturated acids and glycerides, producing addition products. For testing a sample of 0.2 to 0.4 grm. of a liquid, and from 0.8 to 1.0 grm. of a solid fat being used, which is dissolved in 10 c.c. chloroform and treated with 20 c.c. mercury iodo-chloride solution run into it from a burette, if the liquid appear opalescent a further measure of chloroform is introduced, while the amount of mercury iodo-chloride must be such as to produce a brownish coloration of the chloroform for two subsequent hours. The excess of iodine is determined, on addition of from 10 to 15 c.c. potassium iodide solution and 150 c.c. distilled water, by means of caustic soda. From a burette divided into 0.1 c.c. a solution of caustic soda is poured with continual gyration of the flask into the tinged liquid, and the percentage of combined iodine ascertained by difference; for this purpose 20 c.c. of mercury iodo-chloride are tested, on introduction of a solution of potassium iodide and starch, previously to its use as reagent. Adulteration of solid or semi-liquid fats, especially lard, butter, and tallow, with vegetable oils are readily detected by this method, since the latter yield on examination a high percentage of iodine. Animal fats, absorb comparatively less halogen than vegetable fats, and the power to combine with iodine increases with the transition from the solid to the liquid state, and attains its maximum with vegetable oils--the method being adapted to the examination of fat mixtures containing glycerides and free saturated fatty acids, provided that substances which under similar conditions combine with iodine are absent. These conditions are fulfilled with regard to the examination of animal fats and soap. Ethereal oils are also acted upon by iodine; the reaction proceeds similar to that observed in ordinary fat mixtures. Alcoholic mercury iodo-chloride can probably be used with success in synthetical chemistry, as it allows determination of the free affinities of the molecule and conversion of unsaturated compounds into saturated chlorine-iodo addition products.--_Rundschau._

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NOTES ON NITRIFICATION.[2]

[Footnote 2: A paper by R. Warington, read before the Chemical Section of the British Association at Montreal.]

By R. WARINGTON.

In the following brief notes I propose to consider in the first place the present position of the theory of nitrification, and next to give a short account of the results of some recent experiments conducted in the Rothamsted Laboratory.

_The Theory of Nitrification._--The production of nitrates in soils, and in waters contaminated with sewage, are facts thoroughly familiar to chemists. It is also well known that ammonia, and various nitrogenous organic matters, are the materials from which the nitric acid is produced. Till the commencement of 1877 it was generally supposed that this formation of nitrates from ammonia or nitrogenous organic matter was the result of simple oxidation by the atmosphere. In the case of soil it was imagined that the action of the atmosphere was intensified by the condensation of oxygen in the pores of the soil; in the case of waters no such assumption was possible. This theory was most unsatisfactory, as neither solutions of pure ammonia, nor of any of its salts, could be nitrified in the laboratory by simple exposure to air. The assumed condensation of oxygen in the pores of the soil also proved to be a fiction as soon as it was put by Schloesing to the test of experiment.

Early in 1877, two French chemists, Messrs. Schloesing and Müntz, published preliminary experiments showing that nitrification in sewage and in soils is the result of the action of an organized ferment, which occurs abundantly in soils and in most impure waters. This entirely new view of the process of nitrification has been amply confirmed both by the later experiments of Schloesing and Müntz, and by the investigations of other chemists, among which are those by myself conducted in the Rothamsted Laboratory.

The evidence for the ferment theory of nitrification is now very complete. Nitrification in soils and waters is found to be strictly limited to the range of temperature within which the vital activity of living ferments is confined. Thus nitrification proceeds with extreme slowness near the freezing-point, and increases in activity with a rise in temperature till 37° is reached; the action then diminishes, and ceases altogether at 55°. Nitrification is also dependent on the presence of plant-food suitable for organisms of low character. Recent experiments at Rothamsted show that in the absence of phosphates no nitrification will occur. Further proof of the ferment theory is afforded by the fact that antiseptics are fatal to nitrification. In the presence of a small quantity of chloroform, carbon bisulphide, salicylic acid, and apparently also phenol, nitrification entirely ceases. The action of heat is equally confirmatory. Raising sewage to the boiling-point entirely prevents its undergoing nitrification. The heating of soil to the same temperature effectually destroys its nitrifying power. Finally, nitrification can be started in boiled sewage, or in other sterilized liquid of suitable composition, by the addition of a few particles of fresh surface soil or a few drops of a solution which has already nitrified; though without such addition these liquids may be freely exposed to filtered air without nitrification taking place.