Bisulphide of carbon, when diffused in a large volume of atmospheric air, may be introduced into the respiratory organs of living beings, without producing immediate effects; such a mixture, however, will prove fatal when inspired for a sufficient length of time. If the atmospheric air, instead of being loaded with some millionth parts of bisulphide of carbon, contains one-twentieth of this gas in volume, it will act ve*y promptly, death ocur-ing invariably, if its effects are not interrupted in time. M. S. Cloez sometime ago communicated a series of experiments to the French Academy of Sciences on the effects of the gaseous mixtures in question, which he had undertaken with various species of mammalia, birds, and reptiles, with the view of applying them for practical purposes. I. In a first experiment, a large rat was brought under a tabulated bell jar of seventeen liters capacity, after a plug of cotton saturated with bisulphide of carbon had been placed under it. The animal kept quiet in the first instance and seemed to get sleepy, but after half a minute it began to move violently, and attempted to withdraw it3elf from the poisonous atmosphere; its movements, however, soon became slower, convulsive affections followed, the animal fell on one side, its breathing gradually became slow and labored, and death followed some minutes after the commencement of the experiment. II. The second experiment was made with a full-grown rabbit. A sponge impregnated with bisulphide of carbon was held under its nose for a few moments. The animal first kept quiet, but then tried to resist, when it was set at liberty; it soon lost control of its muscles, appearing as if it were intoxicated. It was then forced anew to respire the sulphide of carbon vapors, until a complete insensibility of all its limbs had taken place, when the same phenomena were witnessed as in the first experiment. The sponge, however, was withdrawn when death seemed to have occurred. The rabbit remained in a state of unconsciousness for half an hour, but gradually life returned again; after the lapse of an hour it lifted its head, and, though the posterior extremities still remained paralyzed, it attempted to resume an erect attitude, and after another hour the animal resumed all its functions as if nothing had happened. III. This experiment was also undertaken with a rabbit and forms a repetition of the second one, with the only difference that the poisonous vapors were allowed to act until life was destroyed, which occurred nine minutes after the commencement of the experiment. In dissecting the body, it was found that congestion had taken place at the lower termination of the lungs, and it was also noticed that the right ventricles of the heart continued to contract, though they had been removed from the cavity of the breast, together with the respiratory organs, for over five hours. Upon birds, the bisulphide of carbon appears to act more promptly than upon mammalia. Upon reptiles, however, as might be foreseen, it acts much slower. The respective experiments were undertaken with sparrows and irogs. Experiments on the applicability of bisulphide of carbon, for the extermination of rats and other vermin living underground, were undertaken with rats in the museum for natural history in Paris, where these animals had lodged themselves near the menageries for the wild beasts, andin the neighborhood of the laboratory for comparative physiology. Bisulphide of carbon is now manufactured on a large scale, and may be bought at a comparatively low rate. The mode of its application for the extermination of rats is also very simple. M. Cloez employs for this purpose a lead pipe of a length of from three to five feet, and of suitable diameter, open on both ends, and provided at one end with a small funnel of sheet tin and near the other with some holes, through which the liquid may flow into the rats' nests, in case the lower aperture should get choked up with earth. Before the experimenter proceeded to try his method on a large scale, he made a trial in the small alley which leads to the laboratory for comparative physiology. Here, on an area of fifty square yards, some inhabited rat holes existed, which were connected together by subterranean canals. In one of these holes the lead pipe was pushed as far as possible, while the others were closed with bricks. Fifty grammes of the liquid were poured through the pipe, when the latter was withdrawn and the hole stopped with earth. This method was repeated at the rest of the holes. Two days after the ground was dug up, and not less that fourteen dead rats were found, which had suffocated in their nests. Numerous trials undertaken thereafter in various quarters of the city met with no less satisfactory results. mm m- Limekiln at Imgleton in Yoi-ksliire, England. A new limekiln, constructed on the principle of a German patent, which seems to be a very effective plan, has been erected at the above place. The kiln is oval, and measures in circumference 450 feet, being surrounded by a road for the use of carts. At the hight of four feet from this road there is a platform all round the kiln, six and a-half feet wide. From the platform there are fourteen arched openings into the chambers, for the purpose of taking in the stone and bringing out the lime. Each chamber, which is nine feet in hight at the center of the arch and eighteen feet wide on the floor, is capable of holding 100 tuns of limestone, and, as the stone is calculated to lose by burning two-fifths of its weight in carbonic acid and moisture, a chamber yields at one draw about sixty tuns of lime. As it requires many days to convert the stone into lime, and three days to cool a chamber before it can be discharged, sixty tuns of lime is the amount produced per day. From the platform to the feeding chamber it is in perpendicular hight eleven feet, but as the wall slopes it measures fourteen feet. The feeding chamber extends over the whole of the fourteen lime chambers, and is 150 feet in length and 65 feet in breadth. This chamber, which measures from the floor to the ridge fourteen feet, is covered over with a wooden roof, which cost 200. In this chamber, into which there are forty-one brick openings six and a-half feet high by five feet wide, there are 424 feeding holes, through which, by the use of a small funnel and scoop, the fires are supplied with fuel. In the center of this chamber are fourteen valves 2 feet 1 inch in diameter, connected with the chambers which surround a central chamber in the kiln, called the smoke or carbonic acid chamber, through which the carbonic acid gas and moisture pass through a long flue, and escape i from a brick chimney erected on the top of Meal Bank. As all the smoke is consumed, and the men who feed the fires are under cover, and have only to use a wheelbarrow, a funnel, and a scoop in performing their labor, they can do it with much more cleanliness, comfort, and ease than on the old plan. About 500,000 building and fire bricks, which cost about 1,000, have been used in the erection of the kiln. Why Don't Boys Learn Trades? The Morning Post, published at Philadelphia, answers this inquiry, which recently appeared in the SCIENTIFIC AMEBI-CAN, as follows: It is popular to say that young men should learn trades. Those people are especially fond of saying so to whom manual labor or any extra exertion in the matter oi gaining a living is distasteful. But such self-satisfied advisers apart, young men do, in fact, get the wisest counsel when advised to so employ their youth as to always have at their command in after times some sure means of independence. But how is this desirable end to be obtained ? The entire apprentice system seems destined, under the present tyranny of the Trades' Unions, to be driven out oi existence. It is a rule with many of these societies to refuse to allow their members to work in any shop, office, or factory, with non-members or with apprentices. When the society is powerful and virtually controls the journeymen of its particular craft (as it does in many instances in this city and elsewhere), the door is conclusively shut in the faces of would-be workers in that direction. The employer is quite at the mercy of the society. If he takes apprentices, his journeymen, bound by the articles oi their association, leave him. He cannot replace them, for the good hands are all in the same boat. With the best of feelings, therefore, for the boys who want one day to bejourneymen themselves, what can he do for them ? Nothing. This may be all very well for the mechanics and artisans of the present; but for the future ? While now labor is controlled and good prices obtained, no skilled workmen are growing up. We may be well off, but what is the next generation to do ? We must take care of ourselves, say the Unions. You must, indeed, gentlemen, but it is none the less a fact that such is a short-sighted and illiberal policy that says " there are work-ingmen enough in the world, every individual added to the force diminishes our profit, and, therefore, we combine to keep the body where it is." A reasonable protection to mechanics and others, who have worked to achieve a special excellence in their business, is to be approved, but such exclusivenees, when it comes to the point of shutting young men and boys out of opportunities of learning the best trades, cannot be too strongly condemned. Such a policy will be, in the ond, destructive to industry. Telegraplas—-Europe and United States. The whole number of messages sent in Europe, in 1866, was 18,688,000, and the sum received, $10,329,000 in American gold, or $14,461,000 in currency, at 140. This makes the average cost of these messages 77-J cents each. The Western Uaion Company, which does about 75 per cent of the busi ness in this country, for the year ending June 30, 18G7, transmitted 10,068,000 messages, and received for the same $5,739,-000, equal to 57 cents a message, and in that number is not included the vast amount of railway business, ner the regular dispatches to the press, in which the number of words delivered were 295,000,000, equal to 14,725,000 messages of 20 words each. In Europe the press dispatches are not a tenth part of those in this country. The number of offices to population is vastly greater here than in Europe. In Prussia there is an office to every 33,000; in France, one to 32,000; in Great Britain, one to 14,000; in Belgium, one to every 12,000; in Switzerland, one to every 10,000; and in the United States, one to every 7,500, and in the Pacific states one to every 2,500. So in the use made of the telegraph America stands pre-eminent. In France the number of messages sent is one to every 13 persons; in Prussia, one to every 9; in Great Britain, one to every 5; in Belgium and Switzerland one to every 4; and in the United States, one to every 2J. How to Make Dense Negatives from Engravings, Sufficient density, when reproducing engravings, may be obtained without having recourse to any of those operations which some are pleased to designate as " dodges," but which, so far from earning under such a category, are most legiti-! mate, and useful. Develop with iron somewhat old and peroxi-dized, intensifying with silver and pyrogallic acid; then fix and examine the clearness of the lines. If they are not composed of clean glass, bring about that result by means of a wash of a very weak solution of iodine, followed by one of cyanide of potassium. When the black lines are thus renderedquite clean, and free from any deposited silver, further density is obtained by a reapplication of the silver and pyrogallic acid. Negatives possessing great density may be obtained by first chlorizing the deposit by immersing it for two or three min utes in a solution of three drachms of bicarbonate of potash, and one drachm of hydrochloric acid in twelve ounces of water. After rinsing, pour over the surface a weak solution of sulphantimoniate of sodium (or Schlippie salts) by "which the color will be changed to an intens* and deep scarlet. The Coljden Club Medal. The Cobdsn Club, of London, last summer announced in their organ, the London Star, that they would give a gold medal for the best essay " on the test way of developing improved political and commercial relations between Great Britain and the United States of America." The essays were to be presented to the secretary oftheclubonthelstof January, 1869, and the prize to be awarded by a committee of three of the highest authorities in England, both in economical science and in literary criticism. The cable informs us that the award was made February 26th, to Dr. Joshua Leavitt, of New York city. Dr. Leavitt has been for many years one of the moat earnest and success -ful advocates of sound economical principles in the New York press. The Prize Essay will ba published at once in London, by the Cobden Club, and will be at once republished in the United States. It will be a timely discussion of a subject which is attracting more and more attention, both at home and abroad, as the great questions of the navigation laws, of international coinage, and of tariffs, are becoming better understood in their influences upon international relations.— Evening Post. Quicksilver and 2ron The difficulty of imparting to iron a complete and uniform coating of mercury by dipping it in a solution oi mercury is well known. The process may, however, be very easily accomplished by cleaning the iron first with hydrochloric acid, and then immersing it in a diluted solution of blue vitriol mixed with a little hydrochloric acid, by moans of which it becomes covered with a slightly adherent layer of copper, from which it must freed by brushing, or rubbing with sandpaper, and washing. It is then to be brought into a very diluted solution of mercurial sublimate, mixed with a fow drops of hydrochloric acid. The article will now be covered with a layer of mercury, which cannot bo removed even by hard rubbing. This layer of quicksilver protects the iron from rust, especially if it be washed with spirits of sal ammoniac after the amalgamation. Articles for the laboratory, and for other purposes, coated with quicksilver in this way, and allowed to lie exposed with similar articles not so protected, retain their luster perfectly, while the others "become covered with rust. This same process is especially applicable to the coating of the steel or iron instruments for which oil is generally employed, and will probably be ioiuid to resist the injurious effect of moisture much more perfectly than the oil. Sale Illuminating Oils. Professors Horsford and Doremus have lately made teats of an excellent illuminating oil manufactured from crude petro-lium, the results oi which prove that the flashing point of the oil is about 125 Fah., and the burning point about 145 ' Fah. They say that there is a great want for some more definite mode of determining the safety and value of petroleum oils; and one which could bo practiced l>y the consumers ol the oil, as well as by appointed inspectors. The invention of such an instrument has evidently not received the attention oi inventors which it deserves, and the subject affords an opportunity for some party to bring credit and profit to themselves by supplying the want. This oil is manufactured by Mr. Charles i'liiit, a very reliable dealer, whose advertisement appears in aunt her column. Beware of Benzole. From the facility with which it removes grease spots from fabrics, this substance is regarded almost as a household necessity. But few persons, however, are aware of its explosive character, or the dangers attending the careless handling of it. Being one of the most volatile and inflammable products, it vaporizes with great rapidity, so that the contents of a four ounce phial, if overturned, would render the air of a moderate sized room highly explosive. The greatest care should be taken in handling this substance in proximity to fire, nnd it is important; to remember that the vapor escaping from an uncorked bottle will cause a flame to leap over a space of several feet. Gas on Shipboard. Attention has recently been directed in England to the! practicability of lighting men-of-war with gas manufactured on board. Two vessels in the royal navy arc illuminated with gas, but a correspondent of an English paper states that forty years ago the Duke of York, a steamer carrying mails and passengers between London and the Mediterranean, was lighted with gas, stored in iron bottles, one of which screwed on to the " main," and when the gas contained in it was consumed, a fresh bottle was substituted. A STEONG liquid glue for repairing broken vessels, cpment-ing glass, etc., is made, according to M. Knaff by taking three parts of glue, in small pieces, and placing them in eight parts of water for some hours, when half a part of hydrochloric acid and three quarters o ' a part of sulphate of zinc are added, and the whole kept at a moderately high temperature for ten or twelve hours. The glue thus treated retains its liquid condition, and will not become gelatinous again. A COEBESPONDENT of the Boston Journal of Chemistry, says that water-spouts and sink-spouts frozen up may be speedily thawed out in the following manner : Procure a piece of lead pipe of suitable length and size; place one end against the ice to be thawed, then, through a funnel in the irpper end, pour boiling water. Keep the pipe constantly against the ice, find you can penetrate one foot c-r more vex minute.184Improvement in Hand CultivatorsThis device is calculated primarily for cultivating growing crops, especially those planted in rows, and is intended to supersede, in a measure, the use of the hand hoe, or at least to reduce the labor by that well-known implement, so far as catting down weeds and loosening the soil are concerned. It also may be used for describing and forming furrows for the reception of seed, while it will cover them and compact the earth above them when they have been deposited. Its simplicity of construction and the fact that it is worked entirely by hand are greatly in its favor. These qualities, with their exhibition by actual experiment, have secured forthe machine the first premium at several State and county fairs, and the commendation of all who have tested it. The lower portion (as shown in the position represented In the engraving) presents three shares, or blades, the front one rigidly fixed to an arm, and the two others suspended to pivoted aims, so arranged that one or both may be raised from contact with the ground to adapt the implement to the width of the rows between the growing plants. By reversing the position of the implement tho shovel seen projecting over the wheel may be brought to the ground to make a furrow for the reception of seed. The contrivance is pushed by the operator, like a barrow, before him. The depth of the cultivator blades or shovel may be adjusted by a wedge that holds the block sustaining the blades, and may be, of course, guided as to depth and direction, by the hands of i the operator. Patented through the Scientific American Patent Agency, August 11,1868, by Barnett Taylor. Orders for machines or rights should "be addressed to the patentee, at Forestville, Fillmore county, Minn., or D. E. Runnals, same place, J. L. Michener, Leroy, Mower county, Minn., or R. B. Brown, New Concord, Ohio.Portable Grinding Mlachine for Harvester KnivesMowing and harvesting machines are now so extensively I used that any device that renders them more useful and easier j of application is advantageous to the farmer. Grinding the j knives or cutters of these machines is a work requiring time j and labor, neither of which can be well spared at just the j point when the sharpening is most needed —tho period of gathering the crops. To remove the cutter bar, leave the machine idle in the field, and go to the barn to grind tho knives, requiring the services and time of a man and boy, is quite vexatious. The accompanying engraving shows a portable machine that may be carried to the field and bo a portion of the mower or harvester, ready at all times for use. A bed or frame, A, supports a sliding carriage on which is mounted a grindstone, B, having a gear wheel, C, on its shaft, engagingwith a similar wheel, D, the shaft of which has a crank, E, for giving motion to the stone and its parts. Prom uprights, F, pivoted connections run to a crank on either end of the driving, or crank shaft, and from the same shaft go pivoted bars to tho axle of the stone or grinding wheel. The bearings of this crank shaft are in a vibrating frame pivoted to the base or bed plate of the machine. It will therefore be seen that by turning the crank not only is the stone revolved, but it and all connected with it on the sliding frame, are moved backward and forward. The knives, G, to be grounfl, are seated on a guide, H, fixed to the frame at the proper angle to insure the right bevel to the edge of the blade and held in position by the cutter bar sliding in a corresponding groove in the guide. The face of the stone is razed to a double bevel so that, one side of the two blades is ground simultaneously The reciprocating movement of the stone insures the even grinding of the blades from root to point, and keeps the stone from wearing out of shape, an object that is mora fully secured by the fact that the teeth in tho two gears are odd and eveD, so that no one place on the stone is presented to the blades in two successive revolutions. Tlio stone is hung in vertically-sliding boxes that may be raised or lowered by mea,ns of set screws to adjust the stone to tho blades to be ground. The whole machine can be easily carried by one man, and it requires but one person to operate it. Patented through the Scientific American Patent Agency, January 19, 1869, by Milton Fowks, assignor to himself and A. and J. A. Foote, to whom all orders should be addressed at Catskill, N. Y. State and county rights for sale. —,----------- -----------—Telegraphs versus RoguesThe New York World illustrates the extent of telegraph operations in some comments on the fact that a knavish Chinaman in California having contracted the barbarian vicB of swindling, has been cheating sundry merchants in San Francisco out of $18,000, and, getting on board the Pacific Mail steamship, fleeing to the Central Flowery Kingdom. In this way he hoped to put between himself and those whom he had robbed, first, some 10,000 miles of ocean, but "A telegram from San Francisco bears the tidings of his crime to New York. New York sends it by cable across the Atlantic to London, London through France and under the Mediterranean to Alexandria, Alexandria by the Red Sea and Persian Gulf to Bombay, Bombay to Ceylon, and Ceylon by the Peninsula and Oriental steamers to China. So that when Hong-Kee trips lightly down the ship's gangway at Hong-Kong or Shanghai, dreaming of much opium and many almond-eyed daughters of the Sun in the Land of Flowers, his placid soul will be disconcerted by the tap ot a bamboo on his shoulder and a voice of doom will murmur an ungentle summons in his ear. Poor Hong-Kee! The bad morals of the Christians have corrupted him, and in the steam engine of the Christians has he put his hope. But the literal ' chain-lightning' of the Christians is after him, to outstrip their steam engine, and to teach him in sorrow and in shame how much better is a pot of honest rice and the teachings of Confucius therewith, than many thousands of illegal dollars and a warrant of arrest therewith."Cnemical EquivalentsThe following will convey to a young photographer or a curious reader an idea of chemical equivalents, or combining proportions. It has been found by accurate experiment, that when oxygon and hydrogen combine, they do so in the proportion of eight of tho former to one of the latter; hence the chemical equivalent of hydrogen is 1, that of oxygen 8, sulphur 16, silver 108, etc. These numbers indicate the proportions in which the elementary bodies combine with each other. Stockhardt'sillustrationis one of the simplest that can be adopted : For the same sum can be purchased six ounces of gold, or 12 ounces of platinum, or 100 ounces of silver, or 1,500 ounces of mercury; consequently six ounces of gold have the same mercantile value as 12 ounces of platinum, or 100 ounces of silver, etc. The same principle holds good in chemistry. Twenty-eight ounces of iron, forty ounces of potassium, or two hundred ounces of mercury, combine with eight ounces of oxygen; accordingly twenty-eight ounces of iron have the same chemical value as forty ounces of potassium or two hundred ounces of mercury. By one equivalent, from mquus (equal) and valor (value), of oxygen is to be understood eight parts of it by weight, and the same with the other elementary bodies.Recent Improvements in Electro-metallurgyMr. Kress, in a treatise on this art recently published in Stuttgardt, Germany, describes a new composition (an invention of Mr. Kress) for reverses or molds of objects to be reproduced by galvanic action, from which a faithful cast in gutta percha can not be obtained, as is the case with plates presenting landscapes, etched clouds, or other fine designs in relief or intaglio. While in other cases accurate reverses by means of gutta percha can only he obtained by the application of pressure, this is not the case with the composition of Mr. Kress, which, in assuming a liquid state at a comparatively low temperature, allows the reproduction of all kinds of objects in a uniform manner at a cheaper rate and with less loss of time than heretofore known. In operating with the composition spoken oi it is necessary that the various objects should first be inclosed with a strip of potter's clay. This done, the mass is liquefied and poured over them,care being taken that tho mass be not too hot, as in such a case its subsequent removal would probably be attended with difficulty. It is also indispensable that the original should previously be slightly greased. These precautions being taken, the molds may, when cool, he quite easily lifted from the forms. The finest etched tones in aqua tinta may thus be reproduced faithfully and in a short space of time. The molds are finally rubbed over with fine graphite powder until they acquire a shining black appearance, when they are ready for the bath. The composition, however, is not quite as hard as gutta percha, therefore brushes of the softest kind must be employed, otherwise the surface will be roughened and the work will have to be done over again. The composition itself consists of 12 parts of white wax, 4 parts of asphalt, 4 parts of stearin, and 4 parts of tallow These ingredients are melted together in the following order: 1 Asphalt, as possessing the highest melting point; 2. wax; 3. stearin, and, finally, tallow. When the whole forms a homogeneous liquid, enough soot is stirred into it, to impart to it a fine black color. In order to give to the mass more body and also to prevent its adhesion to the original, some plaster of Paris is mixed witli it. Molds of this composition may not only be taken from medals, dies, and engraved plates, but also from plaster casts. In this case the latter are previously immersed in tepid water until thoroughly soaked, which will have taken place when the generation of air bubbles has ceased. But another method may also be adopted. The plaster cast may be kept immersed in glue water, until, when withdrawn, a drop of glue water will not remain upon the surface. The original is in this case to be greased before cast, and if the glue water has been applied with a brush, which may likewise be done, the model ought to be allowed to dry. Substitutes for glue water are solutions of gum arabic and isinglass. When the copper deposit has been removed from the mold the latter may be used anew, and in case it should ultimately become too brittle by use, it is only necessary to stir a small portion of tallow or yellow wax into the previously liquefied composition. For small objects, as for coins and medals, a simple mixture of wax and stearin has proved to work perfectly well, but for objects of several inches diameter, such a composition would be useless because the contraction which it undergoes is so great as invariably to produce fissures upon its face. Mr. Kress, whose very valuable treatise we would like to see translated into English, furthermore states, that, although all the known and recommended compositions for electrotyping were subjected by him to trial, he had not met with any which answered all purposes so well as the one described. Covering for Tents. The best and lightest material for covering a tent is a thin india-rubber coated fabric, sold by all dealers in india-rubber. It is very light, and quite impervious to both rain and light. Black twilled calico, coated with boiled linseed oil, will form a rain tight cover. Cloth may be rendered waterproof in a variety of ways; for example, brushing it over on the wrong side with a solution of gelatin, followed when dry by an application of an infusion of nut galls. If one is not afraid of an unpleasant smell (of short duration), make a varnish, of india-rubber dissolved in bisulphide of carbon, and apply it to the cloth. PIPE clay rubbed on the hands will remove the unpleasant ordor caused by the use of chloride of lime and salts.