I. SOUUri-.ri. 219 



and carrying with it incandescent particles of powder. The supply and exit 

 air pasages are under and over a series of screens. Air, to support combus- 

 tion, enters the lamp under an inverted outer edge, and then passes through 

 the holes made in the casing to a narrow space formed by an inner lining, so 

 that the air must first pass up to reach the holes in the casing, then down the 

 inner space, and finally up a narrow space between. The top part of the lamp 

 is constructed on substantially the same principle that is, the exit air 

 passages are made zig-zag, two out of three parts which form the passages are 

 hinged to the casing, and are secured by a spring lock. When these parts are 

 unbolted they can be turned back on their hinges, and easily cleared of any 

 soot that may have become deposited in them. The bottom and sides of the 

 lamp are immovable, and the burner is dropped in through the top of the 

 lamp, which is secured with a spring lock, as already mentioned,! Every 

 detail of the outer casing has been carefully considered, and there are no 

 projecting parts where dust can settle and accumulate. The lamp has a bull's- 

 eye in front ; the side lights are glazed with glass one-eighth of an inch thick, 

 protected by strong copper wire. The handle moves on a pivot. The burner 

 is a three-quarter inch flat wick, and a reflector is added to increase the 

 brilliancy. The lamp and lantern are made of copper, bright tin, or tin 

 japanned. The highest temperature ever observed on the outside of the 

 lantern has been 126-, the exploding temperature of gunpowder being 600. 



995. Gas Furnaces. System Perrot. 



Geneva Association for Constructing Scientific Instru- 

 ments. 



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 attaining 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. 3 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 Avaste gases obtained from the top of the 

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

 other is being heated. 



