HOTHOUSE FURNACES. 



253 



ployed in a furnace the better. The use 

 of these plates is for diminishing the area 

 of the grating without lessening the size 

 of the furnace ; and as the fuel upon 

 them consumes very slowly, in conse- 

 quence of receiving no air from below, 

 it continues to burn on them, when that 

 which was immediately above the grating 

 has burnt away. 



In building furnaces, strength and du- 

 rability ought to be considered; there- 

 fore, common bricks should never be 

 used. Fire-clay bricks — a sort containing 

 a large proportion of sand, which renders 

 them exceedingly hard, and capable of 

 resisting for a long time the action of 

 heat — should be invariably employed ; and 

 those of a large size, known in England 

 by the names of Welsh lumps or Stour- 

 bridge lumpers, are to be preferred to 

 bricks of the usual dimensions. Fire-clay 

 should also be used instead of mortar. 



We are at present getting manufactured 

 by the Garnkirk Company, near Glasgow, 

 a complete set of fire-clay bricks for 

 furnaces, as well as a hot-water boiler 

 and flue of the same material, so as to 

 construct either a hot-water apparatus 

 or smoke-flue system of heating, in which 

 not a particle of iron is to be used. The 

 very injurious effects that heated metal- 

 lic bodies have upon the air is so well 

 known, and has been so satisfactorily 

 proved by chemical experiments, that 

 any farther allusion to it here would be 

 superfluous. The following are plans 

 and descriptions of our 

 furnaces. Fig. 335 is 

 the ground-plan, and, 

 like all the other parts 

 of the apparatus, is 

 made of a peculiarly 

 excellent kind of fire- 

 clay bricks and tiles, 

 for which the Garnkirk 

 Company is celebrated, 

 having on theirproperty 

 a species of clay con- 

 taining, by chemical analysis, above twice 

 as much alumina as Stourbridge, consi- 

 dered the best in England, and nearly as 

 much silica ; and as alumina and silica are 

 the only materials that ought to enter 

 into the composition of fire-bricks or 

 crucibles, which are exposed to the most 

 intense temperatures, that clay which 

 contains these in greatest abundance, 



Fig. 335. 



without the presence of lime, peroxide of 

 iron, peroxide of manganese, or phosphate 

 of lime, as the Garnkirk clay does, must 

 be admitted to be the best. The floor of 

 the fire-oven is formed of two fire-clay 

 tiles, 18 inches broad and 2 feet long. 

 The perforated tile a forms the grate 

 upon which the fire burns, and the other 

 the carbonising plate b, upon which 

 fresh supplies of fuel are to be laid. 

 These perforations, as shown in cross and 

 longitudinal sections, figs. 336 and 337, 

 are 1 inch in diameter upon the top 

 surface, and 2 inches in diameter on the 

 under surface, for the admission of air 

 to cause combustion. These tiles are 

 each 4 inches thick. 



The sides of the oven are formed of 

 four bricks, two on each side, 2 feet 

 3 inches long, 6 inches thick, and 12 

 inches broad. These are laid on their 

 edge, and dovetailed together, as well as 

 to the brick at the back of the furnace, 

 which is of the same width and thickness 

 as the side ones, but only 18 inches long ; 

 — they are rounded at the front edge, to 

 ease the draught. The dovetailed bricks, 

 w T hich tie the others together, are 12 

 inches long, passing quite through the 

 side bricks, 12 inches broad, and 16 

 inches thick at the tail end. The 

 utility of these in binding the furnace 

 together must be apparent. 



Fig. 336 is a cross section, showing the 

 perforations in 

 the grate a, 

 the ends of the 

 side brick b, 

 and the roof or 

 coverings. The 

 roof is formed 

 of one semi-cir- 

 cular tile, 4 in- 

 ches thick and 2 

 feet long, covering that part of the furnace 

 which is over the grate, and also the 

 throat of the flue, which are the parts 

 most exposed to intense heat : it is 

 bevelled off at the ends, so as to rest 

 square on the side bricks. The roof 

 over the carbonising plate is a flat tile 

 6 inches thick, 18 inches broad, and 

 2 feet long, contracting this part of the 

 furnace to 12 inches by 18. 



Fig. 337 is a longitudinal section, show- 

 ing the ash-pit door c, which is also of 

 fire-clay, 3 inches thick and 15 inches 



Fig. 336. 



