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when burned, diffuses the same odor as animal bodies do. t is insoluble in cold water,very soluble in alcohol and ether, but after the evaporation ofthese liquids, it is recoveredunchanged. Fats and unctuous oils both dissolve it. It is soluble in carbonated and caus-tic alkaline leys, from which it is precipitated by the acids without alteration. An excessof alkali, however, speedily decomposes it. Nitric acid transforms it into oxalic acid, anda bitter matter. Chlorine makes it white.
The savages mix this pigment with the fat of the cayman or alligator, and rub theirskins with the mixture. It may probably be turned to account in the arts of civilizednations.
CHIMNEY. (Chemincc, Fr.; Schornstein, Germ.) Chimney is a modern invention for promoting the draught of fires and carrying off the smoke, introduced into Englandso late as the age of Elizabeth, though it seems to have been employed in Italy 100years before. The Romans, with all their luxurious refinements, must have had theirEpicurean cookery placed in perpetual jeopardy from their kitchen fires, which, having novent by a vertical tunnel in the walls, discharged their smoke and frequently their flamesat the windows, to the no small alarm of their neighbors, and annoyance of even thestreet passengers.
Chimneys in dwelling houses serve also the valuable purpose of promoting salubriouscirculation of air in the apartments, when not foolishly sealed with anti-ventilating stove-chests.
The first person who sought to investigate the general principles of chimney draughts,in subserviency to manufacturing establishments, was the celebrated Montgolfier. As theascent of heated air in a conduit depends upon the diminution of its specific gravity, or,in other words, upon the increase of its volume* by the heat, the ascensional force maybe deduced from the difference between the density of the elastic fluid in the interior ofthe chimney, and of the external air; that is, between the different heights of the internaland external columns of elastic fluid supposed to be reduced to the same density. In thelatter case, the velocity of the gaseous products of combustion in the interior of the chim-ney is equal to that of a heavy body let fall from a height equal to the difference in heightof the two aerial columns.
To illustrate this position by an example, let us consider the simple case of a chimneyof ventilation for carrying off foul air from a factory of any kind ; and suppose thatthe tunnel of iron he incased throughout with steam at 212 degrees Fahr. Suppose thistunnel to be 100 yards high, then the weight of the column of air in it will be to that ofa column of external air 100 yards high, assumed at 32° F., inversely as its expansion by180° ; that is, as 1000 is to 1*375; or as 72*727 is to 100. The column of external airat 32° being 100 yards, the internal column will be represented by 72*727 ; and the dif-ference=-27*27, will be the amount of unbalanced weight or pressure, which is the effec-tive cause ofphe ventilation. Calculating the velocity of current due to this difference ofweight by the well-known formula for the fall of heavy bodies, that is to say, multiplyingthe above difference, which is 27*27, by the constant factor 19.62, and extracting th esquare root of the product; thus V 19*62 X 27*27 = 23*13 will be the velocity in yardsper second, which, multiplied by 3, gives 60*30 feet. The quantity of air.which passesin a second is obtained of course by multiplying the area or cross section of the tunnel bythis velocity. If that section Is half a yard, that is = a quadrangle 2| feet by 2, we shahave 23*13 X 0*5 = 11*565 cubic yards, = 312f cubic feet. . ^
The problem becomes a little more complicated in calculating the velocity of air wnichas served for combustion, because it has changed its nature, a variable proportion ol *oxygen gas of specific gravity Till, being converted into carbonic acid gas of specifgravity T524. The quantity of air passed through well constructed furnaces may*_'general, be regarded as double of what is rigorously necessary for combustion, andproportion of carbonic acid generated, therefore, not one half of what it would be 'y eall the oxygen so combined. The increase of weight in such burned air of the tempera &of 212°, over that of pure air equally heated, being taken into account in the prece | ^calculation, will give us about 19 yards or 57 feet per second for the velocity in a cmney 100 yards high incased in steam.
Such are the deductions of theory ; but they differ considerably from practical resu e *in consequence of the friction of the air upon the sides of the chimneys, which varies *wise with its form, length, and quality. The direction and force of the winds also exer ^a variable influence upon chimney furnaces differently situated. In chimneys ma ® awrought iron, like those of steamboats, the refrigeration is considerable, and c /^? r j c icdiminution of velocity far greater than what occurs in a factory stalk of well bun 5work. In comparing the numbers resulting from the trials made on chimneys oferent materials and of different forms, it has been concluded .that the obstruction tdraught of the air, or the deduction to be made from the theoretical velocity ois directly proportional to the length of the chimneys and to the square of the ve nC hesand inversely to their diameter. With an ordinary wrought-iron pipe, of from 4