168 Description of a Portable Chamber Blast -Furnace. 



which is also seen in its proper place in fig. 2. supporting i 

 crucible. 



As the construction of this furnace (exclusive of the bel- 

 lows and its stool) is easy to any one at all used to these 

 little manual operations, I trust that the uvrki/ig chemist 

 will allow me to add a few vords on the method which I 

 have found the most convenient and cecononiical. Almost 

 any broken pot of the.proper width will furnish the lower 

 piece A ; and often the middle and vippcr pieces may be 

 contrived out of the same refuse matter. Dr. Lewis ad- 

 vises a saw to cut these pots : but most saws are too thick ; 

 and when a little used, the teeth get rounded oft', which 

 makes them work intolerably slow. I have found bv far 

 the best tool to be an old table knife (or rather two of 

 them) worn thin by use, and hacked and jagged as deeplv as 

 possible by striking the edges strongly against each other. 

 These work well and expeditiously, and when they become 

 dull are again roughened by the same simple means. The 

 holes may be drilled with a common gimlet of the largest 

 size, and a little steadiness of hand will easily enable the 

 operator to give them the oblique direction with sufficient 

 accuracy ; for much is not required. To make a smooth 

 surface to the parts intended to adapt to each other, first 

 ♦ear them down a little with the soft fire-brick, and then 

 grind them with. water on a flat free-stone (a sink-stone for 

 exainple), and lastly make them entirely fit by rubbing one 

 surface on the other. 



No luting of any kind is ever required ; so that the whole 

 may be set up and taken down immediately. Nor is it ne- 

 cessary to bind the pots with metal hoops; for they are 

 thick enough to endure considerable blows without break- 

 ing; and yet they will bear, without cracking, to be heated 

 as suddenly and intensely as possible. In short, the black- 

 lead crucible seems to be the best material that could pos- 

 sibly be devised for these purposes. 



The heat which this little hirnacc will afford is so intense, 

 and so much more than would at first sight be expected from 

 so trifling an apparatus, that it was only the accidental fusion 

 of a thick piece of cast iron in it that led us to suspect its 

 power. The utmost heat which w'c have procured in this 

 furnace has been one hundred and sixty-seven dciirees of" a 

 Wedgwood pyrometer piece, which was withdrawn from a 

 very small Jlessian crucible when actually sinking down in 

 a state of p(;rcellanous. fusion. A steady heat of 150° to 

 l.io" may be usually depended on, if the fire be properly 

 nsansged and the bellows worked with vigour. This is svit- 



1 fie ie fit 



