774 CHIMNEY 



In building chimneys, wo should bo careful to make their area rather too Inrgo 

 than too small ; because wo can readily reduce it to any desired size by means of a 

 sliding register plate near its bottom, or a damper plate applied to its top, adjustable 

 by wires or chains passing over pulleys. Wide chimneys are not so liable as narrow 

 ones to have their draught affected by strong winds. In a factory, many furnace flues 

 are often conducted into one vertical chimney stalk, with great economy in the first 

 erection, and increased power of draught in the several fires. 



Vast improvements have been made in this country of late years in building stalks 

 for steam boilers and chemical furnaces. Instead of constructing an expensive, lofty 

 scaffolding of timber round the chimney, for the bricklayers to stand upon, and to 

 place their materials, pigoon-holos, or recesses, are left at regular intervals, a few feet 

 apart, within the chimney, for receiving the ends of stout wooden bars, which are 

 laid across, so as to form a species of temporary ladder in the interior of the tunnel. 

 By means of these bars, with the aid of ropes and pulleys, everything may be pro- 

 gressively hoisted for the building of the highest engine or other stalks. An expert 

 bricklayer, with a handy labourer, can in this way raise, in a few weeks, a considerable 

 chimney, 40 feet high, 5 feet 8 inches square outside, 2 feet 8 inches inside at the base, 

 28 inches outside, and 20 inches inside at the top. To facilitate the erection, and at 

 the same time increase the solidity of an insulated stalk of this kind, it is built with 

 three or more successive plinths, or recedures, as shown in fig. 455. It is necessary to 

 make such chimneys thick and substantial near the base, in order that they may sus- 

 tain the first violence of the fire, and prevent the sudden dissipation of the heat. 

 When many flues are conducted into one chimney stalk, the area of the latter should 

 be nearly equal to the sum of the areas of the former, or at least of as many of them 

 as shall be going simultaneously. When the products of combustion from any 

 furnace must be conducted downwards, in order to enter near the bottom of the main 

 stalk, they will not flow off until the lowest part of the channel be heated by burning 

 some wood shavings or straw in it, whereby the air siphon is set agoing. Immedi- 

 ately after kindling this transient fire at that spot, the orifice must be shut by which 

 it was introduced ; otherwise the draught of the furnace would be seriously impeded. 

 But this precaution is seldom necessary in great factories, where a certain degree of 

 heat is always maintained in the flues, or, at least, should be preserved, by shutting 

 the damper plate of each separate flue whenever its own furnace ceases to act. Such 

 chimneys are finished at top with a coping of stone-slabs, to secure their brick-work 

 against the infiltration of rains, and they should be furnished with metallic conducting 

 rods, to protect them from explosions of lightning. 



When small domestic stoves are used, with very slow combustion, as has been 

 proposed upon the score of a misjudged economy, there is great danger of the 

 inmates being suffocated or asphyxied, by the regurgitation of the noxious burned air. 

 The smoke doctors who recommend such a vicious plan, from their ignorance of 

 chemical science, are not aware that the carbonic acid gas of coke or coal must bo 

 heated 250 F. above the atmospheric air to acquire the same low specific gravity 

 with it. In other words, unless so rarefied by heat, that gaseous poison will descend 

 through the orifice of the ash-pit, and be replaced by the lighter air of the apartment. 

 Drs. Priestley and Dalton have long ago shown the co-existence of these twofold 

 crossing currents of air, even through the substance of stoneware tubes. True 

 economy of heat and salubrity alike require vivid combustion of the fuel, with a 

 somewhat brisk draught inside of the chimney, and a corresponding abstraction of 

 air from the apartment. Wholesome continuous ventilation, under the ordinary 

 circumstances of dwelling-houses, cannot be secured in any other way. 



The figures upon the following page represent one of the two chimneys erected at 

 the Camden Town station, for the London and North-Western Eailway Company. The 

 chimneys were designed by Kobert Stephenson, Esq., engineer to the company, 

 and executed by William Cubitt, Esq., of Gray's Inn Eoad. In the section.^. 455, 



A represents a bed of concrete, 6 feet thick and 24 feet sqiiare. 



B, brick footings set in cement ; the lower course 19 feet square. 



c, Bramley-fall stone base, with a chain of wrought iron let into it. 



D, a portion, 15 feet high, curved to a radius of 113 feet, built entirely of Malm 

 paviours (a peculiarly good kind of bricks). 



E, shaft built of Malm paviours in mortar. 



F, ditto, built from the inside, without exterior scaffolding. 



o, the cap, ornamented (as shown in the plan alongside) with Portland stone, the 

 dressings being tied together with copper cramps and an iron bond. 

 K, the lightning conducting rod. 



Fig, 456, represents the mouldings of the top, upon an enlarged scale. 

 Fig. 457, a plan of the foundation, upon an enlarged scale. 

 Fig. 458, ditto, at the level of the entrance of the flue as seen in 



