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water; e is a cork, which, in casc gas it contains is forced through explosion happens on the surface the stop-rock, water-tube, and ulof the water, is thrown up, and timately through the safety appawhich takes out, to admit water to ratus and jet at the end of which it be poured into the trough when is burnt. first used; f a guage, which is to "I generally use," says Mr. indicate the necessary height of Gurney, “ my hand to make the the column of water in the trough; necessary force on the press-board, g a transferring bladder, which because I can give it any degree of screws and upscrews to and from pressure I please, and increase or the stop-cock, h, by which the gaso- diminish it as circumstances may meter is charged by an assistant require. The force necessary to during its action, and the quantity keep the flame at the ends of the of gas supplied so as to keep up à respective jets is known in the first flame for any length of time. Be- experiment; for when it is too littween the gasometer and the charg- tle, or the hand is taken off from ing bladder there is a valve placed the press-board, the flame returns to prevent a return of the gas; iia into the safety chamber and the Jight pasteboard or wood cap, con gas is extinguished. Whenever trived so as to unite lightness with you wish to suspend the operation, strength, which in case an explo- and take off the hand from the sion of the gasometer happens, is press-board for that purpose, the thrown into the air by the force water in the trough serves as a rupturing the strings, kkkk, and 'self-acting valve,'in preventing all from its extent of surface and great escape of gas from the instrument, lightness, it is instantly arrested and saves the trouble of turning by the action of the atmosphere. the stop-cock. When weights are To these strings are attached small used instead of the hand, the stopwires, which pass through holes in cock of course must be used in the table of the instrument, ill, every operation. and are again affixed to a moveable “Jets of various sizes are propress-board, m, below; this press- vided, and screw occasionally into board is regulated and kept in a the safety apparatus, at the will of horizontal position by the perpen- the operator. When large ones dicular stand, n, so that when the are used, a little water will somenecessary weight or pressure is times come over with the gas; to placed on it, it may draw the cap, prevent this, I have attached to i, horizontally and equally on the the under end of the tube which is gasometer, d. The gasometer blad- inserted into the water, a little silk der, d, or silk bag, is tied to a tube or bag, which swims through bladder-piece, which screws into a the water to the surface, thus maklong tube, laid into and across the ing a passage for the gas through table of the instrument. This blad- it, without a possibility of splashder-piece, to which the gasometer ing the water. When pressure is is tied, permits it to be unscrewed taken off the press-board, the from the table of the instrument at weight of water collapses and pleasure, and immersed in warm presses the sides of the silk tube water, to render it soft when occa- together, and prevents the escape sion requires; or in case an acci- or waste of gas, without the necesdent happens to it, allows another sity of turning the stop-cock for the to be tied on. To one end of the purpose. But feeling confidence tube, which is let into the table of in the safety of the instrument, I the instrument, the stop-cock of the generally remove the water-trough charging bladder is attached, and entirely, and screw the safety apto the other, the stop-cock of the paratus immediately on to the water-trough.

front stop-cock, by the addition of When pressure is made on the a common connecting piece, when press-board, the cap, ii, is drawn I wish to use a very large jet for down on the gasometer, and the any particular purpose."

CHEMISTRY AS A SCIENCE. the bad taint." It is an excellent Art. VIII.

tooth-powder. If powdered charCARBON.

coal, equal to about one-ninth of CHARCOAL is a substance with the weight of any quantity of water, which most of our readers must be beginning to putrify, be added to it, familiar. It is the first simple sub- the water is rendered quite sweet. stance we have yet mentioned Hence arises the utility of cbarring which has not been discovered in the inside of water casks intended modern times. Charcoal was well to contain water for a long period. known to the ancients; and char. It is the slow decomposition of the coal, when pure, is only another wood in contact with the water, name for carbon. It is obtained or owing to the decomposition of by burning any sort of vegetable some substance the water holds in matter, but particularly wood, in solution, which imparts to it the a close vessel. On a large scale disagreeable taste and smell it it is manufactured by placing a sometimes acquires in long sea great quantity of wood in a heap, voyages. Though charring the insetting it on fire, and covering it side of casks does not cut off this up with sand and clay, or charcoal latter source of putrefaction, it powder and ashes. Whatever wood cuts off the former, and is found of may be used, the charcoal, provid- considerable service. The practice ed it be sufficiently burnt, pos- of employing iron tanks to keep sesses the same properties. By water which has lately been introcommon burning all the volatile duced on board ships, is not only substances, peculiar to different economical, but also preserves the kinds of wood, are not expelled; water from one cause of putrefacand, therefore, to procure it pure, tion. common charcoal must be exposed. New made charcoal absorbs for an hour in a covered crucible moisture with great avidity, so as to the heat of a forge. It is a black, to increase in weight, if left in the shining, brittle substance, without open air, about twelve and a half either taste or smell. It is inso- per cent. When entirely freed from luble in water; and, if all air and air, by being exposed either to a moisture be excluded, is no other- great heat, or to the action of the airwise affected by the most violent pump, it has the singular property heat which can be applied to it, of absorbing a precise and deterthan to become harder and more minate quantity of the different brilliant. It is an excellent con- gases. The most complete and ductor of electricity, and a very satisfactory set of experiments on bad conductor of heat,which makes this subject were made by M. it of considerable use in lining Theodore Saussure. The charcoal crucibles. It is insoluble in water, he employed was that obtained and not liable to corruption. Hence from box wood, and he found great arises the utility of charring the differences in the quantity of gas outside of stakes to be driven into absorbed. Thus one volume of the ground. This property of char- charcoal absorbed 90 volumes of coal was well known to the ancients, ammoniacal gas, 85 of muriatic gas, and in our own time wood has been 65 of sulphurous acid gas, nine and discovered which has been pre- a quarter of oxygen gas, and only served sound from the time of the one volume and three-quarters of Romans, by the outside having hydrogen gas. The absorption was been charred. It is of great use in completed in twenty-four hours, correcting the smell and taste of and was not increased by allowing different substances. If new made the charcoal to remain longer in charcoal be rolled up in clothes contact with the gas. The most which have contracted a disagree- scientific chemists suppose that able odour, the charcoal effectually this effect is analogous to that destroys it. If boiled with meat power of small tubes called capilbeginning to putrify, it destroys lary attraction, by which fluids

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rise in them to a certain height. stances of which the mechanical But if this be the case, how are we properties are more different, and to explain Professor Dobereiner's even contrary, than diamond and experiment, recorded in our last charcoal. The diamond is the From that he infers that the parti- hardest and most beautiful of the cles of hydrogen are smaller than precious stones, and is so exthose of the other gases; and on tremely rare, that immense sums this principle, supposing the ab- of money are given for small spesorption of the charcoal to be oc cimens. It is a beautiful little occasioned by capillary attraction, crystal, dazzling the eye by its more hydrogen should be absorbed brilliancy and its lustre. In its than either of the other gases, while appearance and texture it is the the reverse is the case. Fifty times very reverse of charcoal. It is also more ammoniacal than hydrogen a non-conductor of electricity, while gas is absorbed. The fact of the charcoal is a very good conductor. absorption is curious, and its tak- For many ages it was considered ing place in determinate propor- impossible to burn diamond ; but tions would lead us to suppose Sir Isaac Newton, with that unthat it must be owing to a chemic erring sagacity which seems to cal, rather than to a mechanical have distinguished him beyond all action; particularly as the char- other scientific men, conjectured coal, if put into another gas, will from its property of refracting light give out a portion of that which it so powerfully, that it would burn. has already taken up, and will ab. He had observed that, in general, sorb a portion of the new gas. bodies were combustible in pro

It has already been stated that portion as they refracted light, and charcoal is not altered by exposure hence he was led to conjecture that to heat, if air and moisture be ex- the diamond was combustible, and cluded: but if air be admitted, it that even water contained a combecomes red hot at about the tem- bustible principle. Both these conperature of 8000, and continues to jectures have been amply verified. burn (supposing it pure) till it is It has been ascertained that water totally consumed. The air in which is composed of hydrogen, which is this combustion is carried on is so one of the most combustible matemuch altered by it, that if animals rials; and in 1694, the Florentine breathe it, they die. If small pieces academicians consumed several of dry charcoal be placed on a pe- diamonds by means of burning destal, in a glass jar filled with glasses in the presence of Cosmo oxgen gas, they may be kindled by III. Grand Duke of Tuscany. means of a burning-glass, and con. Since that period this experiment sumed. If the gas be afterwards has been frequently repeated; and examined, it will be found not al- it has been found, by Sir George tered in quantity, but materially Mackenzie, that diamonds will altered in its properties. Lime burn, at a temperature below that water, when allowed to pass into required for melting silver. When the jar, becomes turbid and milky, placed in what is called a mutile, à and absorbs a portion of the gas. little earthen-ware oven, fitted into The gas thus absorbed is called a furnace, if a strong heat is apcarbonic acid gas ; and M. Lavoi- plied to them, they burn with a sier proved that it is precisely low flame, increasing somewhat equal in weight to the charcoal and in bulk, and having their surface oxygen which disappear during covered with crusts of charcoal. the combustion. He therefore con- This latter effect is particularly cluded that the carbonic acid is a observed when they are consumed compound of charcoal and oxygen, in close vessels, by means of burnand that the combustion of char- ing glasses. coal is nothing else but its combina- It was soon ascertained that if tion with oxygen.

air was excluded, the diamonds There are, perhaps, no two sub- underwent no change; and Lavoisier proved that the product of the small portion of hydrogen. When combustion in air or in oxygen gas, chlorine is passed through charwas carbonic acid gas. His expe- coal, which has been previously exriments have since been frequently posed to a very strong heat, muriatic repeated, and others have been acid is formed. When charcoal is instituted with a view to ascertain burnt in dry oxygen gas, moisture the fact: Mr. Smithson Tennant is always formed. By exposing put 120 grains of nitre, and 2.5 charcoal in vacuo, and in condensgrains of diamond into a tube of ed azot, to an intense heat, by gold, and kept the mixture in a means of the voltaic battery, Sir red heat for half an hour. The dia. Humphrey Davy found that a mond was consumed by the ox- small quantity of hydrogen was ygen which the nitre gave out; the produced, and the remaining charcarbonic acid formed was com- coal became so much harder than bined with lime, and afterwards before, that it scratched glass, separated and measured. It was while its lustre was considerably found to be 19.36 inches in bulk, and increased. While this beautiful to weigh 9 grains; these, according experiment almost pointed out the to Lavoisier's calculation, should mode by which diamonds may be contain 2.5 grains of carbon, which formed, it also distinctly proved was the exact weight of the dia that charcoal differs in its chemical mond employed. The proportion properties from diamond, by conof carbonic acid produced from the taining hydrogen. When charcoal combustion of the diamond being is burnt, there is water formed beabout equal to what would have sides carbonic acid; but when diabeen afforded by the same weight mond is consumed, carbonic acid of good charcoal, it was concluded gas is the sole product. that diamond and charcoal were Carbon is very widely diffused the same substance. Common through nature. It forms a very sense rather demurs to this con- large portion of the vegetable kingelusion. There are few or po in- dom, and enters largely into all stances of the different hidden pro those substances such as sugar, perties of matter not being in some gums, resins, oils, &c. which are measure indicated by their palpa- manufactured from vegetables, ble and evident properties. Much Under a particular form, a portion has been stated in various systems of it is constantly given out by all of philosophy, and, in our opinion,' animals, and is generally absorbed very erroneously stated, of the de- by vegetables. It is the basis of lusion of the senses; the fact be- that inexhaustible fund of fuel ing that our senses never delude which makes our homés not only us, though the conclusions which comfortable, but habitable, and men draw, and the things they which more than any other proimagine, very often delude them; duct, of our country, except the but it would indeed be a de- people, has contributed to our nalusion of the most decisive na- tional wealth. In the mineral ture if the chemical, which are kingdom, it forms a part of every the hidden properties of two such variety of lime-stone and of mardifferent substances 'as charcoal ble, and thus enters largely into and diamond, were found to be those material substances which precisely the same. The experi- form the crust of the earth.' ments of M. Lavoisier and of Mr. There is one substance, however, Tennant, have since been repeated of which it forms so large a part, by Messrs. Allen and Pepys, and that we cannot omit mentioning it by Sir Humphry Davy, and the more particularly, this is black lead, conclusion now drawn is, that dia- or as it is otherwise called, plumbago, mond and charcoal have very or graphile. This is a mineral subnearly the same base.' A closer stance, the finest specimens of examination has taught Chemists which are found in the celebratthat charcoal always contains a ed mine of Borrowdale, in the

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