1274
THEORY AND PRACTICE OF ENGINEERING.
Book II.
tubes is open towards the fire-box,and the other towards the chamberin front, where the chimney is placed;there is another door which allowsof the tubes being cleaned out whenrequisite. The iron used for theconstruction of the boiler is mostlyYorkshire plate, g of an iuch in thick-ness, or, where more strength is re-quired, ^ inch, as at the hack, andat other parts only in thickness;the fire-boxes are lapped and rivetedtogether as well as the boilers, carebeing taken that the action of thefire docs not come too strong againstthe parts where the welding is made.Since the introduction of the tubularboilers few accidents have occurredfrom bursting; they were the in-vention of M. Seguin, an engineerat Annonav in France , who patentedthem early in the year 1828 Thesteam occupies the upper part ofthe boiler, from which it passes intoa chamber by two pipes, each ofwhich has three openings or apertures,to admit it before and behind thepiston, as well as to escape up thechimney. The evaporation in theboiler is effected partly by radiantheat communicated to the waterwhich encompasses the fire-box, andpartly by means of the hot air trans-mitted through the tubes. It hasbeen ascertained that 1 superficialfoot exposed to the action of heatedair, as that passing through the tubes,has no more than a third of theeffect when the same area is ex-posed to radiant heat, or has thedirect action of the fire: a locomotivein action, proceeding at the rate ofnearly 19 miles an hour, was foundto evaporate 55 82 cubic feet ofwater during that time, where thesurface exposed to radiation was 43 • 12superficial feet, and that to heatedair 288*35 superficial feet: when anumber of tubes of small diameterare made use of, the temperature ofthe air passing through them shouldbe as nearly as possible that of thewater in the boiler ; there would thenbe little loss- in that which passesoff by the wav of the chimney : butthe heated air is much higher intemperature, which is partly renderednecessary, in the present locomotive,bustion.
JL
m
*\T L in
T#i
. n j
h i rr |
L
11 ll H-nr
. JX-i H ILLJ,
Fig. 2042.
to maintain sufficient draught to carry on
The Regulator Box (fig. 2044.) was first constructed by Mr.Watt ; a spindle passes throughone side of the box, on which a toothed sector moves as a centre, working a rack fixed toa brass valve accurately ground to its seat; the plug tree, part of which is shown under thevalve box, alternately opens and shuts the valve by means of a pin acting on the bent lever,xhe upper arm of which works the toothed sector : this is the form usually applied tostationary double-acting engines, but for locomotives the contrivance shown in fig. 2045. isadopted ; the steam is carried up into a hemispherically crowned cylinder, whence it descendsto the regulator, where the communication is made with the two pipes connected with the