285
lo o inches diameter, attached to an ordinary stove, burning good charcoal, the differenceis prodigious between the velocity calculated by the above theoretical rule, and that ob-served by means of a stop-watch, and the ascent of a puff of smoke from a little tow,dipped in oil of turpentine thrust quickly into the fire. The chimney being 45 feethigh, the temperature of the atmosphere 68° Fahr., the velocity per second was, —
Mean temperature
Trials. By theory. By experiment. of chimney.
1 26.4 feet 5 feet 190° Fahr.
2 29-4 5-76 214
3 34-5 6-3 270
To obtain congruity between calculation and experiment, several circumstances musthe introduced into our formulae. In the first place, the theoretical velocity must beMultiplied by a factor, which is different according as the chimney is made of bricks,Pottery, sheet iron, or cast iron. This factor must be multiplied by the square root ofthe diameter of the chimney (supposed to be round), divided by its length, increased by
four times its diameter. Thus, for pottery, its expression is 2'06 ; d being the di-
ameter, and l the length of the chimney.
■A- pottery chimney, 33 feet high, and 7 inches in diameter, when the excess of its meantemperature above that of the atmosphere was 205° Fahr., had a pressure of hot airoeiual to 1T7 feet, and a velocity of 7-2 feet per second. By calculating from the last•ormula, the same number very nearly is obtained. In none of the experiments did the^elocity exceed 12 feet per second, when tlie difference of temperature was more than^10 Fahr.
-Every different form of chimney would require a special set of experiments to bea u, e for determining the proper factor to be used,d'fr 1S tr °ublesome operation may be saved by the judicious application of a delicate^erential barometer, such as that invented by Dr. Wollaston; though this instrument. e s not seem to have been applied by its very ingenious author in measuring the“Ughts or ventilating powers of furnaces.
‘ mto one leg of this differentia] syphon water be put, and fine spermaceti oil into8 6 °, t ' ler J w e shall have two liquids, which are to each other in density as the numbersof v ^ proof spirit be employed instead of water, we shall then have the relationm e nearl 7 20 to 19. I have made experiments on furnace draughts with the instrumentthe aCa ^ lese slates, and find the water and oil syphon to be sufficiently sensible; forha- Wea ker draughts of common fire-places the spirits and oil will be preferable^Metric fluids. '
found ' lae foteral projecting tube of the instrument, as described by Dr. Wollaston, IW hil 11 Necessary to attach a stop-cock, in order to cut off the action of the chimney,
ac ' n § the syphon, to allow of its being fixed in a proper state of adjustment,viati 0 l s Junction line of the oil and water at the zero of the scale. Since a slight de-ling 0 r ’he legs of the syphon from the perpendicular changes very considerably thetight] v • fo v el, this adjustment- should be made secure by fixing the horizontal pipedoor. * n t0 a roun d hole, bored into the chimney stalk, or drilled through the furnacefespond' a gentl 7 turning the stop-cock, the difference of atmospherical pressure cor-■i 11 n ctinf’y lo the chimney draught, will be immediately indicated by the ascent of theex Perime * ne liquids in the syphon. This modification of apparatus permits the
slowlyyg t0 be readily rectified by again shutting off the draught, when the air willthe stop " enter the syphon; because the projecting tube of the barometer is thrust intoto the zer ° C r ' )Ut not hermetically joined ; whereby its junction line is allowed to returnOht of° °* the sca * e in the course of a few seconds,describlpo- man 7 experiments made with this instrument, I shall content myself withhury ; and B t V ’ Ver !' care ftrlly performed at the breweries of Messrs. Trueman, Han-®raithw a n e a • on ’ an d °f Sir H. Meux, Bart., and at the machine factory of Messrs,trials at the V 1 ^ ^ atter of which I was assisted by Captain Ericsson. In the firstT as lapped ro^ 6 ^ eriaS ’ l ^ e enc * 'he stop-cock attached lo the differential barometerd°°r of a wort' 1 ™ hemp, and made fast into the circular peep-hole of the furnace®qaare and 50 feet'h'’ comrri ’rnicatirirr with two upright parallel chimneys, each 18 inches
°i’ Pressure indicat lnC k Water > or a c °l umn of air 10-7 feet high.IJ 16 ,, ex tremity of ttL* ^“ei'y °f 26 feet per second. In a second settaI1 < of the hl h ®top-cock
This difference
: per second. In a second set of experiments,- the boiler of &M ^‘ c ° clc Wa s inserted into a hole, bored through the chimney&n> a chimney w! Ou “ oa and Watt steam-engine of twenty-horse power. The
muut rose 50 feet ahnv e .* act y ^ inches square at the level of the bored hole, and itsove it. Xhe fire-grate was about 10 feet below that level. On