216 Progress of Practical ~ Theoretical Mechanics ~r Chemistry. At Pouldice, in Cornwall, the tin ores are roasted, to lZacilitate the sub. sequent separation by washing. The furnaces for this purpose have a fire place about one toot by ~bur feet, on the same level as the part destined tbr the ores, and only separated from it by a course of bricks placed flat; the furnace bed is about nine feet six inches by eight feet; the height of the roof one foot; its course nearly horizontal. In the front of the arch, neat, the door, is a vent, which, after rising vertically~ takes a course nearly horizontal, and discharges itself at the distance of a quarter of a mile into a large chimney, the upper part is |brmed of fiat sto_nes~ which are easily removed for the purpose of clearing" out the arsenic accumulated on its sides, which is sold for 10s. per ton: on the outside of the furnace is~ als% a projecting or ibrge chimney, rising about fifteen thet. Similar precau. tions, thvourable to the health of the workmen, are in use in all the tita works throughout England, which have not yet been introduced into Ger. many. The charge of this furnace is six cwt, requiring 1½ bushels of charcoal to each roasting; this is, however variable, as well as the duration of the process, according to the nature of the mineral acted upon. ibid. Notice of Carburet of Potassium, and of a New Gaseous ~li-Carburet of tlydrogen. By EDMUND DAVY, Esq/, Professor of Chemistry to the Royal Dublin Society. (Communicated to tile .British .~s~ociation, 26th ~uffust, 1836.) In January last, the author made ditti~rent experiments to obtain the metal of potash on a large scale, by exposing to a high temperature, in an irou bottle, a mixture of previously ignited tartar and charcoal powder, in pro- portions of the latter varying from about lXo-th to ~th of the whole mass. In one experiment, a substance was obtained of a dark gray eolor~ rather soft to the knife, thougb adhering with tenacity to the iron, and inclining to agranular structure. This substance, when put into water, decomposes it with great tacility, carbonaceous matter is disengaged, and gas copiously evolved, with occasional inflammations on the surface~ as is commonly the case with potassium under similar circumstances. The gas, when, examin- ed, was tound to consist of hydrogen, anti a new bi-carburet of hydrogen, (noticed in a subsequent part of this communication,) in nearly equal vo- lumes. The author regards the substance in question as a mixture of po. tassium and carburet of potassium; the tormer, by its action on water tur- nishing the hydrogen, the latter, the new gas. In collecting gas from the substance, by the action of water over mereury~ a novel and interesting ease of combustion was observed. A little of the substance being placed in a tube filled with mercury, on~ letting up a few drops of water, gas was copiously disengaged, and as the mercury descended along tbe tube, small portions of the substance became ignited,exhibiting the appearance of bright sparks of fire in continued succession. In another experiment with the iron bottle, the author procured no potas- sium, but a small quantity of a substance partly in powder, and partly in small lumps, of a dense black color. This substance the author regards as earburet of potassium. It exhibits no appearance of crystalization to the naked eye; but when viewed with a glass of high magnil]ymg power, the au- thor thinks he has observed congeries of exceedingly minute lour-sided prism% truncated at their solid angles. When the carburet is exposed to Composilion of ~tmospherie Jliv. 217 the air, it soon undergoes changes, oxygen and water appear to be ab- sorbed, and caustic potash and carbon remain. When the carburet is put into water, both substances are decomposed, one portion of the carbon unites with the hydrogen of the water to form the ~ew bi-carbnret of hydrogen, which is the only gaseous product, the remain- der being disengaged, whilst the oxygen of the water and the potassium form potash. Alcohol and turpentine act feebly on the carburet, acids strongly. The carburet undergoes partial decompusition at a dull red heat in close vessels~ potassium slowly rises |rnm it, whilst the carbon remains of a deep and bright black color. The author regards the pure carburet as a binary compound of one propor- tion of carbon and one of potassium. New l~i-earburet of H!/drogen. This gas was obtained by the action of carburet of potassium on water° It is highly inflammable, and when kindled in contact with air, burns with a bright flame, apparently denser and of greater splendor than even olefiant gas. It" the supply of air is limited, the combustion of the gas is accompa- nied with a copious deposition of carbon. When the new gas is brought in contact with chlorine gas instant explosion takes place, accompanied by a large red flame, and the deposition of much carbon,and these effects readily take place in the dark, and are~ of course, quite independent of the action of the sun's rays or of light. The new gas may be kept over mercury for an indefinite time without undergoing any apparent change; but it is slowly absorbed by water. Recently boiled distilled water, when agitated in con- tact with the new gas, absorbs about its own volume of it; but, on heating the aqueous sulution, the gas is evolved apparently unaltered. '1'he gas is absorbed to a certain extent by, and blackens, sulphuric acid. The new gas detonates powerfully with oxygen, especially when the lat- ter [brms three-fourths or more of the mixture, anti the only products appear to be water and carbonic acid gas. It requires fiw its complete combustion ~ volumes of oxygen gas, two volumes of which are converted into carbonic acid gas, and the remaining half volume into water. From the author's analysis by difI~rent methods, the new gas appears to be composed of one volume of hydrogen and ~two volumes of the vapour of carbon condensed into one volume, lts density is therefore less than that of olefiant gas by thewei~htofavolumeofhydrogenequaltothatofitsown bulk. It is, in fact, a bi-carburet of hydrogen composed of two proportions of carbon and one of hydrogen, and may be represented by the formula C ~ + H, or ~ C + H~ and its constitution seems to differ from that of any other known gas. From the brilliancy with which the new gas burns in contact with the at- njosphere, the author thinks it is admirably adapted for producing artificial light, if it can be procured at a cheap rate. R~c. Qen. Seience. Composition of dtmospherie ~ir. M. T. de Saussure has taken advantage of the property which small shot possesses of absorbing oxygen when moistened and agitated with atmospheric air at common temperatures, to analyze common air. He employed a ma- trass possessing a capacity of from 150 to ~50 centi-metres cubes closed hermetically with a metallic stopper, which is fastened with screws to a firm Yon. XIX.--No. $.--Maxtcrb 1837. 19. .