254 SEC. 8. HEAT. 



These may be set up wherever gas is laid on ; the slightest draught is suffi- 

 cient ; and in default of a chimney in the workroom it is enough to let out the 

 funnel through a window pane. The shape of these furnaces varies according 

 to their intended use. There are two principal models, the melting furnace, 

 and the muffle furnace ; the latter is advantageously used for assaying copper, 

 gold, and silver, for roasting minerals, and for melting metals for analytical 

 purposes. 



Temperatures up to 1,300 and 1,400 degrees can be obtained rapidly and 

 with economy, and once obtained can be maintained unchanged during any 

 length of time, and may be reduced at will. 



996. Cowper's Regenerative Fire-brick Hot-blast 

 Stoves. E. A. Cowper. 



The diagrams and model of regenerative fire-brick hot-blast stoves are 

 illustrative of the progress of science as applied to heating the air supplied as 

 a blast under pressure to blast furnaces for smelting iron ores and iron stone. 

 In early times the air was always used cold, but a blast heated in cast-iron 

 pipes was introduced by Mr. J. B. Neilson in 1829, and from that time till 

 the year 1857 the temperature of the blast was generally only about 600 

 Fahrenheit, but by the application of regenerative fire-brick hot-blast stoves 

 the temperature of the blast has been raised to 1400 and 1500 Fahrenheit, 

 and has been accompanied by a very large saving of fuel, amounting in some 

 cases to 7 cwt. o qrs. 14 Ibs. of coke per ton of iron made, whilst at the same 

 time a largely increased make of iron has been produced, varying from 20 to 

 30 per cent, of the original make of iron. The entire wear and tear of cast- 

 iron pipes is avoided, as the air only passes over fire-brick surfaces previously 

 heated by the combustion of the waste gases obtained from the top of the 

 blast furnaces. Two stoves are used alternately, one heating blast whilst the 

 other is being heated. Two or three stoves will heat the blast for two or 

 three blast furnaces. 



996a. Drawings of Bull's Patent Semi-continuous 

 Brick Kilns. Hermann Wedekind. 



These kilns have been worked with great success in India and are now 

 being introduced into this country. . 



They are the cheapest kilns with regard to cost of building and effect a 

 saving of nearly two-thirds of the expenditure usually involved, and are espe- 

 cially suitable for temporary works. 



The effective mode of feeding invented by Hofmann, has also been applied 

 by Bull to his kiln with great success. 



996b. Model of Hofmann's Circular Kiln. 



Hermann Wedekmd. 



Hermann's Patent Annular Ovens for the continuous burning of bricks and 

 tiles, limes and cements, at a saving of from two-thirds to three-fourths of the 

 fuel usually employed. 



It is the joint invention of M. Fred. Hofmann, of Berlin, and M. A. Licht. 

 of Dantzig. 



It is now well known and appreciated by the tra.de in this country, and has 

 been extensively employed by the Government on the extensive works at 

 Portsmouth Dockyard, where five of the kilns have been working at a great 

 saving to the country. About l millions of bricks are daily burnt in them 

 in England alone. Taking coal at an average price of 10s. per ton, this in- 

 vention will give a saving of at least 60,0007. per annum. In burning lime 

 equally favourable results have been realised as in burning bricks. 



