Volume 17 (1868) (428 pages)

The Mining and Scientific Press. 19 Hechanical, The Durability of Materials. NUMBER 1. The durability of metals, like that of organized substanees, depends mainly on the resistance they offer to a combination with oxygen; and thns their deeay may also be regarded as a slow combustion. Dnt their durahility further depends on the character . of the oxides formed on their surface. Iron exposed to moisture will soon he coated with rust, in the form of hydrated peroxides; and as the exides do not adhere to the surface, ndditional flukes constantly form nnd . fall away, until the whole mass is destroyed. Wrought tron ina pure dry atmosphere anffers, practically speaking, no deterioration in any Inpse of time. It is extremely durable in distilled water free from air: but it is slowly oxidized in n moist atmosphere, nnd with fatal rapidity in air or water containing free aeids or other corrosive agents. It is, however, efliciently protected from knch agents by paint, which adheres to elean iron with great tenacity. Itis alson fuet, not hitherto satisfactorily acconnted for, that oxidation is tea grent extent arrested by vihration’ The painting of wrought-iron girders and roofs, more especially in tho neighborhood of smoky towns, is a precaution of tho ntmost importance. Hvery eare shonld ho taken to expose tho irou as freely as possihle to the air, to leave no hollows where watcr can collect, to avoid tho contact of damp earth, nnd especially of vegetation, and to throw tho material into the form of heavy bars rather than thiu plates, Painting is more economically performed, and more efiectual, when constantly attended to, than under the vicious practice of laying on three or four eoats, and then leaving the work for years, till the paintall pecls off, with a layer of rust attached to it. Tho Britannia Bridge furnishes a striking Ulustration of the value of this system. The maintenance had heen effected hy two or three men, constantly on the work, who attended to the slightest symptom of local discoloration. As a consequence, the author did not hesitate to express his firm belief, that the total loss from rnst of the 10,540 tons of which the tubes consisted, did not in twenty years amount toa single pound weight. Cast iron, when exposed to the action of sea water, slowly decomposes the iron; being dissolved, leaving behind a graphite or plumbago. ‘The action is, however, superficial, and very slow. It cau he preserved by painting, where accessible for that purpose, or hy any protection which prevents eontinual renewal of the surrounding medium, 2s when inelosed in brickwork or masonry. In fresh water it suffers no such deterioration, and under ordinary cireumstances its durability in a pure atmosphere appears unlimited. In the case of zine, although the bright metal oxidizes even more rapidly than iron, yet the oxide adheres witb such tenacity to the metal tbat it affords an efficient proteetion against the continuation of the process. To this property tho metal owes its great durability, more especially as its oxide is insoluble in water. In the presenee of any solvent of the oxide, this metal is so speedUy destroyed as to be practically nseless, unicss proteeted by paint. Tho destruction of zine in smoky districts is, however, principally due to galvanie action. A siinilar action produces the rusting away at the base of iron railings, when fixed in stonework, as is usually the euse, by being run in with lead. The contact of copper with the irou plates of a vessel is also a source of great danger; and there are numberless other instances iu which the contact of metals of different conducting powers is equally destruetive. In all such cases the use of paint furnisbes, at any rate, a temporary remedy. It is difficult to over-estimate the value of the introduction of the process of eoating iron plates with vine, by simply eleaning and immersing them in the molten metal. . All that has been saidon the subject of zine applies equally to galvanized iron, as it is ealled. In oelear atmosphere its great dnrability, its stiffucss, its freedom from expansion, and its economy, are all qualities of the highest value; while, on tho other hand, witbout eonstant painting, itis wholly unfitted for the atmosphere of smoky towns, or manufactories, or even stations where it is exposed to the fumes from locomotives. Both the eorrosive and the galvanic actions, which in such cases are so destructive, do not cease witb the destruction of zinc, which is soon nffected but eontinnes also to aet, . with fatal effect, upon the iron itself, as may he seen in many railway stations and } and carbonic acid in moist air. sheds near the manufacturing towns. Tho corrosive tendency in zine and iron obliges the use of less oxidizahle metals, copper and lead. Lead slowly absorhes oxygen Tt is acted upon by certain waters, and is occasionally ridWed with holes hy the larvn of an insect; and its expansion and contraction requires to Le allowed for in its use, Its ductility render it a valuable material. Copper might, however, in many instunees, be nsed with great advantage in its stead. The action of sen water on copper is so importont that it was particularly alluded to. The cbjcet in covering a vessel with copper is solely to prevent the adhesion of harnaeles and other molluscs. This property is not dne to the poisonous quality of its salts, as is sometimes asserted, nor is eopper used on aeconnt of its durable qualities; on tho contrary, its valne depends on its slow destruction. The chloride of copper formed beneath the attachment of the harnaclo being a soluble salt, the creature no sooner effects a lodgeihent than it is at onco set free by the solntiou of the salt; while the salts which forms on zine or iron being insolnhle, the plate is rather protected than otherwise hy the tenactons parasite. Hence the difficulty of devising an eflicient paint for iron ships; for while, ou the one hand, it must be slowly solnhle in water to prevent this adhesion, it must, on the other hand, he sufficiently insoluble to he durahle. Ordinary oil paint is the most efficient material for protecting either metals or wood from theefiects of moisture and nir; but all oils, resins, and gums exposed to air, and especially to the light of the snn, oxidize and huru away with more or less rapidity, leaving a powdery residue behind. As a preservative of paint against tho heat of the sun and light, attention was directed to tho virtue of a coating of silicious sand, dredged on the paiut while wet, The durability of matter is a snbject of the highest philosophieal interest. The universal law on this planet appears to be that no form shall he permanent. Neverceasing destruction and reconstruction are characteristie, within the range of the atmosphere, of everything that exists, whether as regarded organie life orinorganie matter; and it is prohable that even the atmosphere itself is suhject to the same decree. Excrnient Extry Wuerus, which may be used witb water, as are grindstones, are made by dissolving gum shellae in aleohol, mixing the emery with it and pouting and pressing in molds. Good wheels may also be made hy a mixture of glue, dissolved, and emery, treated in a similar manner. Ordinary wheels are made hy covering the periphery of a wooden disk, snitably secured to a mandrel, with folds of woolen or eanton flannel, and covering the whole with leather or strong cloth. Upon this is placed a eoating of emery sceured by zine, Tue town of Winehendon, Mass., elaims to manufacture more wooden ware than any otber town in the world. Two of the largest firms turn out $500,000 and $200,000 respectively, and the smaller establishments of the place make the aggregate annnal product of the wooden ware interest mount up to over $1,000,000. In addition tothese factories, Winchendon contains two cotton mills, two bobbin mills, two machine shops, and two sewing machine manufactories. Stern is successfully alloyed with other metals, improving its qualities for some purposes. One five hundredth part of silver adds immensely to the harduess of steel and yet increases its tenacity. One hundredth part of platinum, though not forming so hard an alloy as the silver and steel, gives a very great degree of toughness. Rhodium, palladium, iridium, and osmium, make steel very hard, but tbeir use, from their cost, is confiued mainly to the experimental laboratory. l Driaiep vs. Puxcerp Hoxrs.—A large numher of specimens of steel plates were recently tested at Chatham Dock-yard, to determine the differenccin streugth between steel plates with punched and drilled holes. The advantage in teusile strain, gained when the holes are drilled rather than puuched, was calculated to be 22.5 per cent, Durima the summer, twelve or fifteen largo iron furnaces are to he erected in Lehigh Connty, Peunsylvania, Sctentifie Miscellany. Science in the Arts. A somewhat remarkable instanco of the vnluo of seience to tho arts is cxemplitied in tho recent development of a new industry, under tho direction of Messrs. Maumend & Nagelet, of Paris. This is pronounecd one of tho most singular discoverics in the history of agricultnre. It has long heen known that sheep draw a considcrahle quantity of potash from tho land upon which they graze, much of which is excreted from the skin with the perspiration of tho animal; and it has been shown by Chevreul that this peculiar potash compound, which is known as ‘‘snint,” forms no less than one-third the weight! of raw merino wool; while of ordinary wools it constitutes ahout fiftecu per cent, of the ficcce. As this eomponnd is soluble in cold water, +-it is easy for the wool manufacturer to produce a more or less eoncentrated solution of the same, and from which tho potash may be reeovered by an appropriate treatment. The process of this treatment constitutes tho new industry alluded to, and which is now being introduced into the principal woolen mannufactorics of France, The plan adopted by Messrs. Maumené & Ragelet is a very simple one, and is descrihed as follows: They eyaporate the solutions which are sent to them, until a perfectly dry and somewhat charred residue has been ohtained. This is placed iu retorts and distilled, very much in the same manner that coal is distilled at gas-works ; and the result is that, while mueh gas is evolved, which can he used for illuminating the factory, and much ammonia is expelled, which ean he collected and utilized in many ways, there remains a residne, which chiefly eonsists of earhonates, sulphate, and chloride of potassium. These three salts are separated by the usual method, and then pass into commerce. Curiously enough, they are remarkably free from soda. Some idea may he formed of the prospective magnitude of this new industry, from the fact that there are nearly 50,000,000 fleeces washed annually in France, which wonld yield, if all subjeeted to this process, not less than $2,800,000! Sheep fecding, it is well known, is very exhuustive to the soil, The facts above developed make elear tho manner in which this deterioration occurs, and points outthe remedy. The potassic eonstituents so extensively drawn upon must be supplied ; it is a duty the farmer owes to the soil,—the neglect of it is but little short of a erime to the community. The entire development of the above series of facts affords a most practieal illustration of the valne of scienco in the arts. Passace or Hyprocen tHrovucnH Iron ar 4 Low Tremprrature.—Not long ago we gave sone aecount of tbe transmissihility of gases through cast irov at high temperatures. To-day we give an interesting experiment which shows that hydrogen will pass through cast iron at the ordinary temperature. M. Cailletet took au iron flask with a long (curved) neck, exhausted the nir from it, and placed the mouth under mercury. ‘he body of the flask was then set iu a vessel of dilute sulphuric acid, The outer surface was, of course, attacked by the aeid and hydrogen evolved, some of which passed into the interior of the fiask, and, driving out the mercury, escaped iu bubhles from tbe trough. There may be more iu this experiment than M. Cailletct suspects. Hydrogen passes into metals with most remarkable facility, und Mr. Graham believes is liquified with them.— Mechunics’ Magazine. Exgcrricity In Vacvo.—Mr. Alvergniat, of Paris, has constructed anew apparatus for proving that electricity cannot pass throngh an absolute vacunm. ‘Two platinum wires areinserted into a tube so that their free ends are within about au eighth; of an inch of each other, ‘The «iy is then exhausted from the tube ‘iy means of a . mercurial column, nfter which the electric . spark will not pass from one platinum wire . to the other. ‘ A Sarcvnomerer,—M. Coret has recently deviscd an instrument—a saturomcter— which is intended to be affixed to steam beilers which use salt water, to determine the degree of saturation and at the same time to reeord tho level of the water in the boiler. Tho action of tho instrument depends on tho well-known principle that when two different liquids, having the same temperature and no chemical affinity, are placed in an inverted syphon, their hights in eaeh column, under the condition of equilihrium, will be inversely as their densities. ‘Iwo glass tubes, communicating with each other at the hottom, are placed side hy side with a gradnated scale between them. One tube is eonnected with the feed-water, and the other with the water in the hoilers ; so arranged that when the eomparison is to be mado the connections are cut off. It is said tho accuracy of this apparatus permits a nearer approach to the point of saturation than formerly, thus obviating the difliculties and loss of heat arising from an unnecessarily frequent “‘blowing off,” to remove the excess of saline deposits from the hoiler. To Exrcrro-Puars Parrr or orper F'1Brous Marertau.—A mode has been devised for depositing eopper, silver or gold, hy the electric process, upon paper or any other fibrous material. This is aceomplished by first rendering the paper a good conductor of electricity, without coating it with any material whieh will peel off. One of the hest methods is to take a solution of nitrate of silver, pour in liquid ammonia till the precipitate formed at first is entirely dissolved again ; then place the paper, silk, or muslin, for one or two hours in this solution. After taking it out and drying well, it is exposed to a current of hydrogen gas, hy which operation the silver is reduced to a metallie state, and the material becomes so good a conductor of electrieity that it may be electro-plated witb copper, silver or gold in the usual manner. Material prepared in this manner may be employed for various useful and ornamental purposes, Consvustion.—The perfect combustion of one ton of antbracite eoal or of eoke, requires over 5,970 pounds of oxygen, derived from abont 340,000 eubie feet of air at ordinary temperature, equivalent to a eolumn one foot square and over sixty-four miles in length. This ealculation is based upon the supposition thatall of the oxygen of the air is made available, but in practice it is found necessary to introduce twiee the qnantity of air that by calculation would he sufficient. In the conversion of one part of solid earbon into carbonie oxide, there are involved 2,473 heat units. Inthe eonversion of the earbonie oxide thus obtained, into carbonic acid, there are involved 5,607 heat units, making 8,080 heat units in all, of whieh the first or imperfeet eombustion yiclded but thirty-one per eent. of the obtainable heat ; so that to limit the supply of air so as to cause the exclusive production of carbonie oxide, would necessitate the use of three times as much fuel as would be required to do the same work were it properly burned. Gut Wirr.—The gilt wire employed in making gold lace soon tarnishes. The surface of gold seldom being perfeetly eontinuous, sulphur gets at the metal beneath, whether copper or silver, and the wire quiekly blackens, To avoid this result, M. Helouis proposes to insert a thin layer of platinum between the copper and the gold. Todo this, he drives a bar of copper into a ring of platinum strongly heated. ‘The eoutraction of the platinum on eooling fixes it firmly to the eopper, and tbe wire may be drawn without any risk of sepnrating the two metals. The gilding may be done as usual. The eolor obtained is as good as that of silver gilt wire, and, of course, lasting, for sulphur will have no effect, on tbe platinum. In 1829, there wero but three miles of railway track iu the United States; to-day. there are not less than 38,500 miles. ‘The railroad business of the Untan employs ebout 500,000 men.

The Mining and Scientific Press. 19 Hechanical, The Durability of Materials. NUMBER 1. The durability of metals, like that of organized substanees, depends mainly on the resistance they offer to a combination with oxygen; and thns their deeay may also be regarded as a slow combustion. Dnt their durahility further depends on the character . of the oxides formed on their surface. Iron exposed to moisture will soon he coated with rust, in the form of hydrated peroxides; and as the exides do not adhere to the surface, ndditional flukes constantly form nnd . fall away, until the whole mass is destroyed. Wrought tron ina pure dry atmosphere anffers, practically speaking, no deterioration in any Inpse of time. It is extremely durable in distilled water free from air: but it is slowly oxidized in n moist atmosphere, nnd with fatal rapidity in air or water containing free aeids or other corrosive agents. It is, however, efliciently protected from knch agents by paint, which adheres to elean iron with great tenacity. Itis alson fuet, not hitherto satisfactorily acconnted for, that oxidation is tea grent extent arrested by vihration’ The painting of wrought-iron girders and roofs, more especially in tho neighborhood of smoky towns, is a precaution of tho ntmost importance. Hvery eare shonld ho taken to expose tho irou as freely as possihle to the air, to leave no hollows where watcr can collect, to avoid tho contact of damp earth, nnd especially of vegetation, and to throw tho material into the form of heavy bars rather than thiu plates, Painting is more economically performed, and more efiectual, when constantly attended to, than under the vicious practice of laying on three or four eoats, and then leaving the work for years, till the paintall pecls off, with a layer of rust attached to it. Tho Britannia Bridge furnishes a striking Ulustration of the value of this system. The maintenance had heen effected hy two or three men, constantly on the work, who attended to the slightest symptom of local discoloration. As a consequence, the author did not hesitate to express his firm belief, that the total loss from rnst of the 10,540 tons of which the tubes consisted, did not in twenty years amount toa single pound weight. Cast iron, when exposed to the action of sea water, slowly decomposes the iron; being dissolved, leaving behind a graphite or plumbago. ‘The action is, however, superficial, and very slow. It cau he preserved by painting, where accessible for that purpose, or hy any protection which prevents eontinual renewal of the surrounding medium, 2s when inelosed in brickwork or masonry. In fresh water it suffers no such deterioration, and under ordinary cireumstances its durability in a pure atmosphere appears unlimited. In the case of zine, although the bright metal oxidizes even more rapidly than iron, yet the oxide adheres witb such tenacity to the metal tbat it affords an efficient proteetion against the continuation of the process. To this property tho metal owes its great durability, more especially as its oxide is insoluble in water. In the presenee of any solvent of the oxide, this metal is so speedUy destroyed as to be practically nseless, unicss proteeted by paint. Tho destruction of zine in smoky districts is, however, principally due to galvanie action. A siinilar action produces the rusting away at the base of iron railings, when fixed in stonework, as is usually the euse, by being run in with lead. The contact of copper with the irou plates of a vessel is also a source of great danger; and there are numberless other instances iu which the contact of metals of different conducting powers is equally destruetive. In all such cases the use of paint furnisbes, at any rate, a temporary remedy. It is difficult to over-estimate the value of the introduction of the process of eoating iron plates with vine, by simply eleaning and immersing them in the molten metal. . All that has been saidon the subject of zine applies equally to galvanized iron, as it is ealled. In oelear atmosphere its great dnrability, its stiffucss, its freedom from expansion, and its economy, are all qualities of the highest value; while, on tho other hand, witbout eonstant painting, itis wholly unfitted for the atmosphere of smoky towns, or manufactories, or even stations where it is exposed to the fumes from locomotives. Both the eorrosive and the galvanic actions, which in such cases are so destructive, do not cease witb the destruction of zinc, which is soon nffected but eontinnes also to aet, . with fatal effect, upon the iron itself, as may he seen in many railway stations and } and carbonic acid in moist air. sheds near the manufacturing towns. Tho corrosive tendency in zine and iron obliges the use of less oxidizahle metals, copper and lead. Lead slowly absorhes oxygen Tt is acted upon by certain waters, and is occasionally ridWed with holes hy the larvn of an insect; and its expansion and contraction requires to Le allowed for in its use, Its ductility render it a valuable material. Copper might, however, in many instunees, be nsed with great advantage in its stead. The action of sen water on copper is so importont that it was particularly alluded to. The cbjcet in covering a vessel with copper is solely to prevent the adhesion of harnaeles and other molluscs. This property is not dne to the poisonous quality of its salts, as is sometimes asserted, nor is eopper used on aeconnt of its durable qualities; on tho contrary, its valne depends on its slow destruction. The chloride of copper formed beneath the attachment of the harnaclo being a soluble salt, the creature no sooner effects a lodgeihent than it is at onco set free by the solntiou of the salt; while the salts which forms on zine or iron being insolnhle, the plate is rather protected than otherwise hy the tenactons parasite. Hence the difficulty of devising an eflicient paint for iron ships; for while, ou the one hand, it must be slowly solnhle in water to prevent this adhesion, it must, on the other hand, he sufficiently insoluble to he durahle. Ordinary oil paint is the most efficient material for protecting either metals or wood from theefiects of moisture and nir; but all oils, resins, and gums exposed to air, and especially to the light of the snn, oxidize and huru away with more or less rapidity, leaving a powdery residue behind. As a preservative of paint against tho heat of the sun and light, attention was directed to tho virtue of a coating of silicious sand, dredged on the paiut while wet, The durability of matter is a snbject of the highest philosophieal interest. The universal law on this planet appears to be that no form shall he permanent. Neverceasing destruction and reconstruction are characteristie, within the range of the atmosphere, of everything that exists, whether as regarded organie life orinorganie matter; and it is prohable that even the atmosphere itself is suhject to the same decree. Excrnient Extry Wuerus, which may be used witb water, as are grindstones, are made by dissolving gum shellae in aleohol, mixing the emery with it and pouting and pressing in molds. Good wheels may also be made hy a mixture of glue, dissolved, and emery, treated in a similar manner. Ordinary wheels are made hy covering the periphery of a wooden disk, snitably secured to a mandrel, with folds of woolen or eanton flannel, and covering the whole with leather or strong cloth. Upon this is placed a eoating of emery sceured by zine, Tue town of Winehendon, Mass., elaims to manufacture more wooden ware than any otber town in the world. Two of the largest firms turn out $500,000 and $200,000 respectively, and the smaller establishments of the place make the aggregate annnal product of the wooden ware interest mount up to over $1,000,000. In addition tothese factories, Winchendon contains two cotton mills, two bobbin mills, two machine shops, and two sewing machine manufactories. Stern is successfully alloyed with other metals, improving its qualities for some purposes. One five hundredth part of silver adds immensely to the harduess of steel and yet increases its tenacity. One hundredth part of platinum, though not forming so hard an alloy as the silver and steel, gives a very great degree of toughness. Rhodium, palladium, iridium, and

osmium, make steel very hard, but tbeir use, from their cost, is confiued mainly to the experimental laboratory. l Driaiep vs. Puxcerp Hoxrs.—A large numher of specimens of steel plates were recently tested at Chatham Dock-yard, to determine the differenccin streugth between steel plates with punched and drilled holes. The advantage in teusile strain, gained when the holes are drilled rather than puuched, was calculated to be 22.5 per cent, Durima the summer, twelve or fifteen largo iron furnaces are to he erected in Lehigh Connty, Peunsylvania, Sctentifie Miscellany. Science in the Arts. A somewhat remarkable instanco of the vnluo of seience to tho arts is cxemplitied in tho recent development of a new industry, under tho direction of Messrs. Maumend & Nagelet, of Paris. This is pronounecd one of tho most singular discoverics in the history of agricultnre. It has long heen known that sheep draw a considcrahle quantity of potash from tho land upon which they graze, much of which is excreted from the skin with the perspiration of tho animal; and it has been shown by Chevreul that this peculiar potash compound, which is known as ‘‘snint,” forms no less than one-third the weight! of raw merino wool; while of ordinary wools it constitutes ahout fiftecu per cent, of the ficcce. As this eomponnd is soluble in cold water, +-it is easy for the wool manufacturer to produce a more or less eoncentrated solution of the same, and from which tho potash may be reeovered by an appropriate treatment. The process of this treatment constitutes tho new industry alluded to, and which is now being introduced into the principal woolen mannufactorics of France, The plan adopted by Messrs. Maumené & Ragelet is a very simple one, and is descrihed as follows: They eyaporate the solutions which are sent to them, until a perfectly dry and somewhat charred residue has been ohtained. This is placed iu retorts and distilled, very much in the same manner that coal is distilled at gas-works ; and the result is that, while mueh gas is evolved, which can he used for illuminating the factory, and much ammonia is expelled, which ean he collected and utilized in many ways, there remains a residne, which chiefly eonsists of earhonates, sulphate, and chloride of potassium. These three salts are separated by the usual method, and then pass into commerce. Curiously enough, they are remarkably free from soda. Some idea may he formed of the prospective magnitude of this new industry, from the fact that there are nearly 50,000,000 fleeces washed annually in France, which wonld yield, if all subjeeted to this process, not less than $2,800,000! Sheep fecding, it is well known, is very exhuustive to the soil, The facts above developed make elear tho manner in which this deterioration occurs, and points outthe remedy. The potassic eonstituents so extensively drawn upon must be supplied ; it is a duty the farmer owes to the soil,—the neglect of it is but little short of a erime to the community. The entire development of the above series of facts affords a most practieal illustration of the valne of scienco in the arts. Passace or Hyprocen tHrovucnH Iron ar 4 Low Tremprrature.—Not long ago we gave sone aecount of tbe transmissihility of gases through cast irov at high temperatures. To-day we give an interesting experiment which shows that hydrogen will pass through cast iron at the ordinary temperature. M. Cailletet took au iron flask with a long (curved) neck, exhausted the nir from it, and placed the mouth under mercury. ‘he body of the flask was then set iu a vessel of dilute sulphuric acid, The outer surface was, of course, attacked by the aeid and hydrogen evolved, some of which passed into the interior of the fiask, and, driving out the mercury, escaped iu bubhles from tbe trough. There may be more iu this experiment than M. Cailletct suspects. Hydrogen passes into metals with most remarkable facility, und Mr. Graham believes is liquified with them.— Mechunics’ Magazine. Exgcrricity In Vacvo.—Mr. Alvergniat, of Paris, has constructed anew apparatus for proving that electricity cannot pass throngh an absolute vacunm. ‘Two platinum wires areinserted into a tube so that their free ends are within about au eighth; of an inch of each other, ‘The «iy is then exhausted from the tube ‘iy means of a . mercurial column, nfter which the electric . spark will not pass from one platinum wire . to the other. ‘ A Sarcvnomerer,—M. Coret has recently deviscd an instrument—a saturomcter— which is intended to be affixed to steam beilers which use salt water, to determine the degree of saturation and at the same time to reeord tho level of the water in the boiler. Tho action of tho instrument depends on tho well-known principle that when two different liquids, having the same temperature and no chemical affinity, are placed in an inverted syphon, their hights in eaeh column, under the condition of equilihrium, will be inversely as their densities. ‘Iwo glass tubes, communicating with each other at the hottom, are placed side hy side with a gradnated scale between them. One tube is eonnected with the feed-water, and the other with the water in the hoilers ; so arranged that when the eomparison is to be mado the connections are cut off. It is said tho accuracy of this apparatus permits a nearer approach to the point of saturation than formerly, thus obviating the difliculties and loss of heat arising from an unnecessarily frequent “‘blowing off,” to remove the excess of saline deposits from the hoiler. To Exrcrro-Puars Parrr or orper F'1Brous Marertau.—A mode has been devised for depositing eopper, silver or gold, hy the electric process, upon paper or any other fibrous material. This is aceomplished by first rendering the paper a good conductor of electricity, without coating it with any material whieh will peel off. One of the hest methods is to take a solution of nitrate of silver, pour in liquid ammonia till the precipitate formed at first is entirely dissolved again ; then place the paper, silk, or muslin, for one or two hours in this solution. After taking it out and drying well, it is exposed to a current of hydrogen gas, hy which operation the silver is reduced to a metallie state, and the material becomes so good a conductor of electrieity that it may be electro-plated witb copper, silver or gold in the usual manner. Material prepared in this manner may be employed for various useful and ornamental purposes, Consvustion.—The perfect combustion of one ton of antbracite eoal or of eoke, requires over 5,970 pounds of oxygen, derived from abont 340,000 eubie feet of air at ordinary temperature, equivalent to a eolumn one foot square and over sixty-four miles in length. This ealculation is based upon the supposition thatall of the oxygen of the air is made available, but in practice it is found necessary to introduce twiee the qnantity of air that by calculation would he sufficient. In the conversion of one part of solid earbon into carbonie oxide, there are involved 2,473 heat units. Inthe eonversion of the earbonie oxide thus obtained, into carbonic acid, there are involved 5,607 heat units, making 8,080 heat units in all, of whieh the first or imperfeet eombustion yiclded but thirty-one per eent. of the obtainable heat ; so that to limit the supply of air so as to cause the exclusive production of carbonie oxide, would necessitate the use of three times as much fuel as would be required to do the same work were it properly burned. Gut Wirr.—The gilt wire employed in making gold lace soon tarnishes. The surface of gold seldom being perfeetly eontinuous, sulphur gets at the metal beneath, whether copper or silver, and the wire quiekly blackens, To avoid this result, M. Helouis proposes to insert a thin layer of platinum between the copper and the gold. Todo this, he drives a bar of copper into a ring of platinum strongly heated. ‘The eoutraction of the platinum on eooling fixes it firmly to the eopper, and tbe wire may be drawn without any risk of sepnrating the two metals. The gilding may be done as usual. The eolor obtained is as good as that of silver gilt wire, and, of course, lasting, for sulphur will have no effect, on tbe platinum. In 1829, there wero but three miles of railway track iu the United States; to-day. there are not less than 38,500 miles. ‘The railroad business of the Untan employs ebout 500,000 men.