BRICK 



531 



and from the stiffness of the clay used, loss water has to bo evaporated in the drying, 

 thus saving one half the time required for hand-made bricks, and avoiding the risk of 

 loss from bad -weather. 



The following remarks by Dr. Ure are deserving of attention : 



' The brick kilns and clamps round London and other large cities, which are fired 

 with the breeze rubbish collected from dust-holes that contain the refuse of kitchens, 

 &c., emit, in consequence, most unpleasant effluvia ; but brick kilns fired with clean 

 coke or coal give out no gases of a more noxious nature than common household 

 fires. The consideration of this subject was closely pressed upon my attention on 

 being consulted concerning an injunction issued by the Chancellor against a brick 

 clamp in the Isle of Wight, fired with clean coke-cinders from the steam-engine fur- 

 nace at Portsmouth Dockyard. The bricks, being of the description called sand stock, 

 were of course made in moulds very slightly dusted with sand, to make them fall 

 freely out. The sand was brought from Portsmouth Harbour, and, on being subjected 

 to a degree of heat more intense certainly than it could suffer in the clamp, was 

 thought to give out traces of hydrochloric acid. 



' As it is well known to the chemist that common salt strongly ignited in contact 

 with moist sand will emit hydrochloric acid, there was nothing remarkable in the 

 above observation ; but I ascertained that the sand with which the moulds wore 

 strewed would give out no hydrochloric acid at a heat equal at least to what the 

 bricks were exposed to in a clamp 10 or 12 feet high, and fired at its bottom only 

 with a layer of "cinders 3 or 4 inches thick. But I further demonstrated that the 

 entire substance of the brick, with its scanty film of sand, on being exposed to igni- 

 tion in a suitable apparatus, gave out not hydrochloric or any other corrosive acid, 

 but ammonia gas. Hence, the allegations that the clamp sent forth a host of acid 

 gases to blight the neighbouring trees were shown to be utterly groundless ; on the 

 contrary, the ammonia evolved from the heated clay would act beneficially upon 

 vegetation, while it was too small in quantity to annoy any human being. A few 

 yards to leeward of a similar clamp in full activity, I could perceive no offensive 

 odour. All ferruginous clay, when exposed to the atmosphere, absorbs ammonia from 

 it, and of course emits it again on being gently ignited.' 



Floating bricks are a very ancient invention ; they are so light as to swim in water ; 

 and Pliny tells us that they were made at Marseilles, at Colento, in Spain, and at 

 Pittane, in Asia. This invention, however, was completely lost until M. Fabroni 

 published a discovery of a method to imitate the floating bricks of the ancients. 



xki 



