ON PHYSICS, OR NATURAL PHILOSOPHY. No. XXXVIII.

(Continued from page 160.)

CALEFACTION.

Spheroidal State.-When liquids are poured on incandescent metallic substances, they present remarkable phenomena, which were first observed by Leidenfrost, about a century ago, and which have been since studied by some philosophers. It is to M. Boutigny d'Evreux, however, that we owe the knowledge of certain curious and important facts on this subject. It has been long known that when drops of water are thrown upon red-hot iron plates, they assume a globular form, and employ less time in vaporising in proportion to the degree of heat attained by the plates. This property, which has been carefully studied by M. Boutigny, is called by him calefaction; and the bodies found in such a state are said to be in the spheroidal state. If a capsule (a small cup) made of silver or platinum, of considerable thickness, be powerfully heated, and a few drops of water be dropped into it by means of a pipette, it is observed that the liquid does not spread itself, nor wet the capsule, as it does at the ordinary temperature; but that it assumes the form of a flattened globule. In this state the water takes a rapid gyratory motion at the bottom of the capsule, and not only does it refuse to enter into ebullition, but it vaporises fifty times more slowly than if it were in the boiling state. Moreover, if the capsule be cooled, there will happen an instant when it is not sufficiently hot to preserve the water in the spheroïdal state; its sides are then wetted by the liquid, and suddenly a violent ebullition takes place.

All liquids may assume the spheroidal state, and the temperature of the capsule in which the phenomenon is produced is more elevated in proportion as the boiling point of the liquid is higher. Thus in the case of water, the capsule must be heated to, at least, 200° Cent. or 392° Fahr.; and in that of alcohol to 134° Cent. or 2730.2 Fahr. M. Boutigny has observed that the temperature of liquids in the spheroidal state is always lower than that of their state of ebullition, as in the following examples :

Liquids. Water ... Alcohol Ether

Sulphurous Acid (liquid) 10 5

Spheroïdal Temperature. 95.5 Cent. or 203°.9 Fahr. 75 5 167 9 34 93 2 13 1 99 Notwithstanding this reduction of temperature in the spheroïdal state, the temperature of the vapour produced by the liquids in this state is equal to the temperature of the capsule; whence it follows that this vapour is not produced in the mass of the liquid. This property of liquids, by which they preserve a lower temperature than that of their ebullition, has led M. Boutigny to the discovery of a remarkable experiment, that of the congelation of water in an incandescent capsule. He heated a platinum capsule to a white heat, and poured into it some drops of anhydrous sulphurous acid. This liquid, which boils at -10° Cent. or 14° Fahr., behaves in the capsule like water; that is, its temperature sinks below -10° Cent. If, then, there be added to the sulphurous acid, a small quantity of water, the latter, being cooled by the acid, is instantly frozen; and the capsule being still red-hot, we take out of it, to our great surprise, a piece of ice.

In the spheroïdal state there is no contact between the liquid and the heated body. M. Boutigny proved this by the following experiment:-he made a silver plate red-hot, and placed it perfectly horizontal; he then poured on it some drops of water coloured black, and this liquid passed into the spheroïdal state: next, he placed the flame of a candle at a certain distance, in a line with the plate, when the flame was distinctly visible, for some time, between the spheroid of water and the plate. Whence he concluded that the liquid was kept at a small distance from the plate, or that it made its vibrations so rapid that the eye could not distinguish them. In order to give the explanation of the phenomena of the VOL. Y.

spheroïdal state of liquids, it is supposed that the liquid globule is supported at a distance from the vessel by the tension of the vapour which is produced at its surface, so that the liquid not being heated by contact, but only by radiation, is converted into vapour very slowly; and the more so, because water being diathermous to rays emitted from an intense source, the greater part of the radiant caloric traverses it without heating it. M. Boutigny considers that the cause which hinders the liquid from wetting the metal is a repulsive force which is generated between the liquid and the heated body; a force which becomes greater in proportion as the temperature of the latter becomes more elevated. This hypothesis agrees with the following observation made by Mr. Perkins. A stop-cock having been placed on a steam-boiler below the level of the water within it, the liquid would not run out by the stop-cock, when opened, if the sides of the boiler were raised to a very high temperature, although the interior pressure was very great; but if the temperature of the sides was lowered, the liquid would rush out with considerable force.

In accordance with the results of these curious researches on the spheroïdal state of liquids, M. Boutigny has latterly connected the phenomena of calefaction with facts formerly deemed incredible, and which now-a-days are fully substantiated. It had been asserted that men ran bare-foot upon melted metal in an incandescent state, plunged their hands into melted lead, etc. Coupling these assertions with the stories of trial by fire, and incombustible men, he was desirous of verifying these phenomena. After some unsatisfactory efforts, he found that in founderies some workmen, more hardy than others, passed their fingers into incandescent cast metal; and some ran bare-foot upon a trough of melted iron which had just issued from the furnace, etc. He himself passed one hand right through a stream of red-hot iron about a quarter of an inch broad, and dipped his other hand into a vessel full of incandescent metal of the same description. He repeated this trial at the Mint in Paris, and plunged his hand, without hurt, into a mass of silver in a state of complete fusion. M. Boutigny considers that there is no contact between the hand and the metal; the perspiration with which the epidermis or under-skin is always more or less impregnated, passing into the spheroïdal state, reflects, without absorption, the radiant heat proceeding from the melted mass, and does not heat it enough to throw it into a state of ebullition. Whatever may be the explanation of these facts, well authenticated now, they completely account for the reality of the frequent success of the trials by fire, in the days of ignorance and barbarism.

DENSITY OF VAPOURS.

By the Density of a Vapour is meant the ratio between the weight of a certain volume of that vapour and the weight of the same volume of air, at an equal temperature and pressure. Two methods have been followed in the determination of the density of vapours; the first, employed by Gay-Lussac, is applicable to liquids which enter into the state of ebullition below 100o Cent. or a little above it; the second, adopted by M. Dumas, may be employed in the case of temperatures which may rise to about 400° Cent. or 752° Fahr. The apparatus of Gay-Lussac is represented in fig. 198.

It is composed of a cast-iron vessel filled with mercury, in which a glass cylinder, M, is immersed; the latter is filled with water or with oil, of which the temperature is indicated by a thermometer, T. In the interior of the cylinder is a graduated bell-shaped glass, c, which is at first filled with mercury. In experimenting with this apparatus, the liquid to be vaporised is introduced in a small glass bubble, represented at a, on the left of the figure; this bubble being then hermetically sealed, it is weighed; and by subtracting from its weight thus found, its weight when empty, we have the weight of the liquid it contains. The bulb is then introduced into the glass c, and the apparatus is gradually heated until the water in the cylinder reaches a temperature higher by some degrees than that at which the liquid in the bubble would enter into the state of ebullition. The bubble then bursts by the expansion of the liquid it contains, and by the tension of the vapour into which it is converted, the mercury. in the glass is depressed, as shown in the figure. It is necessary that the bubble be so small as to allow of all the liquid 116

Fig. 199.

represents the weight of the vapour which is formed in the glass c. As to the volume of this vapour, it is ascertained by means of the graduated scale on the glass. We have only now to calculate the weight of a volume of air equal to that of the vapour, and to divide the weight of the vapour by that of the air; the quotient is the density or the specific gravity required.

The process which we have thus described is not applicable to liquids whose boiling points exceed 150° or 160° Cent., that is, 302 or 320° Fahr. The reason is, that in order to raise the oil with which the cylinder is filled to these temperatures, the mercury, in the vessel must be heated to a degree considerably higher, a degree at which it produces vapour from the mercury which it would be dangerous to inhale. Besides, in the graduated glass vessel, the tension of the mercurial vapour would increase that of the vapour which is the subject of experiment, and would thereby become a source of error in

the result.

The following process, invented by M. Dumas, can be employed at any temperature up to that at which the glass would become soft and flexible, that is, about 400° Cent. or 752° Fahr. The apparatus is composed of a hollow glass globe, B, with a tapering neck, fig. 199, and capable of holding about a pint of water. This globe is completely dried within and without, and weighed when it contains air only, which gives r the weight of the glass. The liquid to be vaporised is then introduced at the tapering point, and the globe is next immersed in a water-bath saturated with salt, or in a bath of neat's-foot oil, or of D'Arcet's alloy, according to the temperature of the ebullition of the liquid contained in the globe. In order to keep the latter in the bath, there is fixed on one of the handles of the pot or vessel which contains it, an iron rod which is furnished with a sliding support of the same metal. The support carries two rings, between which the globe is placed, as shown in the figure. On the other handle is fixed a rod of the same kind, which carries a thermometer, D. The globe and the thermometer being immersed in the bath, the latter is heated a little beyond the boiling point of the liquid in the globe; then the vapour, as it issues through the extremity of the neck, drives out the air in the apparatus; and, at the

when the globe is cooled and carefully wiped, it is weighed again, and the weight, r', thus obtained, represents the weight of the vapour it contains plus the weight of the glass, minus the weight of the air displaced. To obtain the weight of the vapour, therefore, we must subtract from the weight ' the weight of the glass, and add to the remainder the weight of the air displaced, which will be easily done after the volume of the globe has been found. To determine this, the neck of the globe is immersed in the mercury, and its extremity is there broken off with a pair of small pincers. As the vapour is condensed, there is a vacuum created in the globe; and the mercury rushes into it by the pressure of the atmosphere, and completely fills it, if all the air has been forced out of it. Then by pouring into a graduated vessel, the mercury which fills the globe, we determine its volume at the ordinary temperature. By calculation we easily deduce from this, the volume of the vapour at the temperature of the bath, and con. sequently the volume of the vapour at the same temperature. Having ascertained by this process, as well as by that of Gay-Lussac, the knowledge of the weight of a certain volume of vapour, at a determinate temperature and pressure, the density of the vapour may be ascertained by calculation. If any air remains in the globe, it will not be completely filled with the mercury; but the volume of mercury introduced will still represent the volume of the vapour. The following table shows the densities of some vapours as compared with that of air, at temperatures a little higher than that of the boiling points of the liquids from which they are generated:

Table of the Densities of Vapours.
Vapours.
Common air
Vapour of water

alcohol

...

Densities. 1.0000

0.6235

do.

1.6138

Problem 1. To find the density of a vapour when the weight of the vapour in grains, its volume in cubic inches, its tempe rature in Centigrade degrees, the height of the barometer, and the height of the mercury in the bell-shaped glass are given.

Let p denote the weight of the vapour in grains, its volume in cubic inches, t its temperature in Centigrade degrees, H the height of the barometer in inches, and h the height of the mercury in the glass vessel also in inches; it is required to find D the density of the vapour.

At 0° Centigrade, and at the standard atmospheric pressure, 61 cubic inches of air weighs twenty grains, p. 242, vol. iv.; consequently one cubic inch weighs of a grain, and the weight of the volume v of air is v. In order to find the weight of the same volume of air at the temperature t, let a be the co-efficient of the expansion of air; then the volume will be increased from 0° to to in the ratio of 1 to 1+at; on the contrary, the weight under the same volume, varies in the inverse ratio of 1+at to 1. Therefore, the weight of the volume v of air, at the temperature t, and under the standard pressure, is (A). But the weight of the same 61 (1 + at) volume of air being proportional to the pressure, we pass from the standard pressure, which we denote by s, to the pressure H-h, - by multiplying the quantity (A) by the fraction

which gives

20 v

S

20 v (H h) 61 8 (1 + at) v, at the temperature t, and at the standard pressure. sequently, we have for the required density, D =

for the weight p' of a volume of air

61 ps (lat)

20v (H 砂

P

μ

Con

=

Problem 2. To find the volume of a given weight of vapour in the state of saturation, at a given temperature, its density being known.

Let it be required to find the volume of twenty grains of the vapour of water at 100° Centigrade and at the standard pressure, the density of this vapour with relation to that of air being 06235. In order to find the weight of a cubic foot of the vapour of water at 100° Centigrade, in other words, of steam at the standard pressure, we must multiply the weight of a cubic inch of air at the same temperature and pressure by 0-6235. Now we have seen that representing by the weight of a certain volume of air at t° Centigrade, by r the weight of the same volume at 0° Centigrade, and by a the co-efficient of the expansion of air, we have PP' (1+ a t), see p. 126, vol. v.; therefore p' Whence, in the case under consideration the weight of a cubic inch of dry air at 100° Centigrade =24 of a grain; consequently, the 61 (1+0.003665 × 100) weight of a cubic inch of saturated vapour at 100° Centigrade, or steam, at the standard pressure, is 24 × 0·6235014964 of a grain. Whence the volume v of twenty grains of steam is

is

20

0.14964

20

P

1 + at

133.65 cubic inches.

In conclusion, we may observe that at 0° Centigrade a cubic inch of water weighs nearly 253 grains, and when this is converted into steam, or vapour at 100° Centigrade, without loss, it will still weigh the same; therefore, we have this proportion, as twenty grains : 253 grains :: 133.65 cubic inches: 1690 66 cubic inches, the volume occupied by a cubic inch of water when converted into steam. Hence, we see that the vapour of water at 100 Centigrade and at the standard pressure of the atmosphere, occupies nearly 1700 times the volume of the water which produced it; so that mechanics are accustomed to say, in round numbers, that a cubic inch of water produces about a cubic foot of steam.

BIOGRAPHY.-No. XIV.

JAMES WATT, INVENTOR OF THE STEAM-ENGINE. THE celebrated James Watt was born at Greenock, formerly the port of Glasgow, on the 19th January, 1736, of a family said to have been remarkable for mathematical talent. His father was an active and respectable merchant of that town, and was one of its magistrates for many years. Young Watt

was prevented from receiving much benefit from the dayschools of his native town, by the extreme delicacy of his constitution, a physical defect which adhered to him through life. A defect of this kind, indeed, is one of those predisposing circumstances which scarcely ever fail to exercise a powerful influence on the future fortunes of the individual. How many of the most eminent artists, poets, and philosophers who adorned the age in which they lived, have been indebted to such apparently unfortunate accompaniments of birth, for that power and depth of reflection which have afterwards immortalised their names. Take the following instances. Pope, "who lisp'd in numbers, for the numbers came," was forced by the delicacy of his constitution to look for enjoyment chiefly in the retirement of domestic life; Pascal, Fontenelle, Samuel Johnson, and a host of other illustrious men, have found their only relief from the pains of disease in the absorption of mind induced by literary and philosophical studies. In later times, the illustrious examples of Scott and Byron are well known, and serve to confirm the assertion made by judicious and experienced writers, that occasional defects and weaknesses of the physical frame are amply compensated by the grasp of mind and the development of talent which arise from study, and from the reflective habits consequent on retirement from the world's gay scenes of fancied enjoyment. No doubt, those intensely studious habits which distinguished Watt during his long career, may in a great measure be attributed to the delicacy of his constitution in early life, to which we have alluded.

purpose of learning the business of a mathematical instrument At the age of eighteen young Watt went to London for the maker; and during a stay of twelve months, he made very Some time after his return from the metropolis, when he was considerable proficiency in various branches of mechanical art. only twenty-one, he was appointed "Mathematical Instrument maker to the University of Glasgow," then celebrated for the ability and reputation of its professors, and adorned by the Geometry, Dr. Adam Smith, the founder of Political Economy, illustrious names of Dr. Robert Simson, the restorer of ancient and Dr. Black, the able co-adjutor of Priestley, Scheele, and Lavoisier, in erecting the noble fabric of modern Chemistry.

Whether it was that his occupation did not find him sufficient employment, or whether it was that the weakness of his health and constitution had an effect on his movements, it is difficult now to say, but we have heard from some of the old inhabitants of Glasgow, persons of a similar turn of mind to Watt himself, that he was remarked by his neighbours in the vicinity of his workshop to be a very lazily-inclined young man, and that if he continued to be so idle as they thought he was, he never would do any good. His workshop was situated at that time in King-street, and there, no doubt, he performed the experiments which afterwards conferred so much renown on his would get upon the roof of his workshop, and bask in the sun name. We have been told, on the same authority, that he for half the day, apparently. doing nothing; but it is evident that while his body was thus at rest, his mind was deeply occupied with some philosophical inquiry. Let not, therefore, young persons of a thoughtful turn of mind be always judged too harshly, should they not appear to be so actively engaged as they ought to be.

The

It was during his residence in Glasgow under these circumstances, that Mr. Watt was employed by the Professor of Natural Philosophy, to repair a model of Newcomen's steamengine, for the purpose of exhibiting it to the students in working order. This took place in the year 1763. difficulty which he found in supplying the engine with steam, first suggested to him the idea of making a separate condenser; and by means of a set of experiments, which he made on the occasion, he was enabled to ascertain the exact quantity of heat consumed in the vaporisation of water. For some account of the various methods which Mr. Watt adopted in bringing the steam-engine from one step of improvement to another, the mechanical ingenuity which he displayed in varying the forms of the materials of the different parts of its machinery, and the philosophical facts which he established by his numerous and well-conducted experiments, see "Cassell's History of the Steam-Engine." It is of great importance to make this remark for the encouragement of plodding industry, that scarcely any of his improvements could be attributed to

chance or accident; for all those changes which ended in the complete remodelling of the steam-engine, are solely to be ascribed to his practical skill as an artist, and to his profound acquaintance with the sciences of chemistry and mechanics. Rarely, indeed, has there met in one individual such a combination of natural sagacity, practical ingenuity, and real science. Here, however, it may not be amiss to observe that many common workmen have, by constant reading, deep study, and careful observation, acquired a knowledge of art and science, not only far beyond their equals, but surpassing even those who were college-bred, and who enjoyed much more favourable opportunities for learning. Of such individuals, the two philosophical bakers of Glasgow, to whom we were indebted for the preceding anecdote of Watt, were remarkable specimens. We have seen their shop filled with the ingenious seekers of knowledge in that city; we have seen them take a handful of flour, scatter it equally over a board, like the sand of the ancients, and portray the parts of a steam-engine upon it with the finger, in order to explain the principles of operation, as discovered by Watt, as improved by others, or as suggested by themselves. We have seen them portray the parts of a telescope or other optical instrument, and explain the principles of operation in the same way, to their admiring friends. Nothing came amiss to them and to their philosophical flour-board; they had something to say on every mechanical or chemical subject that could be named; and they were held in universal esteem. But fortune smiled on them; wealth was left to them by a relative; they retired from business; and the coterie of philosophical friends which used to meet in their shop was broken up.

To return to our memoir. Mr. Watt, in 1765, entered into partnership with Dr. Roebuck (the founder of the Carron Iron Works, Scotland), for the purpose establishing a manufactory of steam-engines. This object, however, was not immediately accomplished; the causes which prevented this were the embarrassments in which Dr. Roebuck became involved, and the constant employment which Mr. Watt began to enjoy as a civil engineer.

In 1767, he was engaged on the survey of a proposed junction canal between the Forth and the Clyde, and afterwards he made the survey of the canal between the Monkland collieries and the city of Glasgow, a work of which he also superintended the execution. He likewise made surveys of a proposed canal between Perth and Forfar, and drew up a report of another between the Clyde and the Western Ocean, across the isthmus of Crinan. It would be too long to enumerate here the various surveys, plans, and estimates which he made, for the making of canals, the deepening of rivers, the building of bridges, and the construction of harbours. The last line of country which Mr Watt surveyed for a canal, was that between Fort William and Inverness, being part of the Caledonian Canal, a project which was afterwards undertaken and carried into effect by Mr. Telford, the celebrated engineer. Not long after he made this survey, he accepted the invitation of Mr. Boulton of Soho, near Birmingham, and settled in England. In 1775, he obtained an extension of the term of the patent which he had taken out for his improvements, and the business of manufacturing steam-engines was at last begun by Messrs. Boulton and Watt. The immense saving obtained by this powerful engine soon caused its speedy adoption not only in the mines of Cornwall, but in those of England generally. During the years from 1781 to 1785 inclusive, Mr. Watt took out a number of patents for successive improvements in mill-work connected with his engines, such as the movement of the sun and planet wheels, the working on the expansive principle, the double-acting engine, the parallel motion, and the smokeless furnace. The machine was finally brought to perfection by the application of the centrifugal regulating force of the governor. In the whole of these inventions, and the contrivances necessary to give them full effect, we are impressed by a union of philosophical research, physical skill, and mechanical ingenuity, which has, we believe, no parallel in modern times.

The perfection thus given to the rotative steam-engine soon led to its general application for imparting motion to almost every species of mill-work and machinery; and thus an impulse, unexampled in the history of inventions, was given to the manufactures, the population, and the wealth of the

kingdom. Among other inventions of this ingenious man, was a copying apparatus, for which he took out a patent; and amid the multifarious concerns of an extensive business, he gave close attention to the new discoveries in chemistry, which were changing the face of that science; and he himself added to its domain, by the discovery of several remarkable properties of the gases. In 1756, he introduced into this country the new method of bleaching by chlorine (or oxymuriatic acid) discovered by M. Berthollet. This discovery he communicated to his father-in-law, Mr. Macgregor, a bleacher in the neighbourhood of Glasgow; and he himself not only gave directions for the proper construction of the necessary vessels, but superintended the first trials that were made in the process. The successful result of these trials is well known, as well as the astonishing advances which have been made in our manufactures by the discovery. Besides these more important subjects, there were few practical arts which he did not cultivate and improve, and with which he was not intimately conversant.

For several years of his life, Mr. Watt was harassed by the necessity of defending his patents against a host of invaders; but the validity of his claims was finally decided by the Court of King's Bench in 1799; and in the following year, he retired from business. He still continued after that period to interest himself in the progress of science, literature, and the arts; and till the end of his life he was always ready to give assistance and advice to others. Notwithstanding his very delicate constitution, by temperance and good management, he reached the advanced age of eighty-four, with his faculties unimpaired. After a short illness he expired at his seat in Heathfield, Staffordshire, on the 25th of August 1819. He was chosen a Fellow of the Royal Society of Edinburgh in 1784; of the Royal Society of London in 1785. The degree of Doctor of Laws was conferred on him by the University of Glasgow in 1806; and he was chosen in 1808, Corresponding Member, and afterwards one of the eight Foreign Members, of the Royal Institute of France.

On the 18th of June, 1824, a public meeting was held in London for the purpose of erecting a monument to the memory of this illustrious man. At this meeting, the first men of the age met and made the most eloquent speeches in honour of the inventor of the steam engine. The talented and eloquent Francis Jeffrey, editor of the "Edinburgh Review," and afterwards Lord Advocate of Scotland; the celebrated Henry Brougham, afterwards Lord Chancellor of England; and many other noblemen and gentlemen, spoke on this occasion. This splendid meeting many of our readers will no doubt remember, and they have most likely treasured up some of the fine sayings uttered on that memorable occasion. In the following November, there was also held a public meeting in Glasgow for the purpose of erecting a monument to Mr. Watt in that city or in its vicinity. As the men who spoke at this meeting were more intimately acquainted with Mr. Watt than the former, and as Glasgow was the scene of his early labours and inventive genius, we may be permitted to lay before our readers a few of the facts and sentiments brought to light on that occasion, by giving some extracts from the speeches then and there delivered, from a document now lying before us. The Lord Provost of Glasgow, who was in the chair, said: "That as the idea of erecting one grand monument to the memory of Mr. Watt, in Westminster Abbey had not succeeded, he hoped that it would be superseded by the more successful efforts of that day, and by their contributions to the erection of one which would at once perpetuate his memory and adorn the city which gave birth to those mighty efforts of his genius,-his improvements on the steam-engine."

Professor Jardine said: "My Lord, I am one of the earliest and certainly one of the oldest friends of the late Mr. Watt. I had the happiness of living with him in habits of intimacy and friendship the greatest part of my life. I was particularly acquainted with him at the period when he was engaged in prosecuting those discoveries which have set him so far above all other men as an inventor in the arts. I then enjoyed much of his confidence, and was present at many of his early experiments. When Mr. Watt had made such progress in his invention as to afford a favourable prospect of the result, he found that other experiments must be made to satisfy the public, on a larger and much more expensive scale than he was