182 MEASUREMENT OF HIGH TEMPERATURES. Lbull.1 
This is given in front elevation and longitudinal section in Fig. 37 an 
in side elevation in Fig. 38, respectively, drawn one-fourth and one-ha 
tbe actual size. The body of the furnace is shown at B B B B, a thicl 
walled cylindrical pot, surmounted by a hemispherical dome, A A J 
the lid of the furnace. A central hole at A' and a series of six syrr 
metric lateral holes, a a, a a, . . .in the lid are sufficient for the escap 
of the products of combustion. 
The burners HRHH and G G G G project into the furnace as far a 
the inner surface. Their diagonal position is well shown in the sid 
elevation (Fig. 38) and their internal construction in the longitudim 
section of Fig. 37. Compressed air from a centrifugal blower, run by 
one horse-power gas engine, enters the central tubes li h and gg 1 resped 
ively. The inlets of gas are shown at c and c'. Attached to the boi 
torn of the burners are rectangular slides II and K K, respectively 
which pass through guides L L and ill if. In this way the burners ca 
be easily inserted or withdrawn from the furnace. A little pin, I 
prevents their being inserted too far into the interior, and a simila 
longer pin or roller, e, is so adjusted as to rest the greater part or th 
whole of their weight upon the bed plate S #, instead of on the friabl 
mass of the furnace. The burners shown in the figure were constructe 
entirely of gas pipe, and the disposition of parts is such as suggeste 
itself after many trials. Burners in which back explosion is obviate 
by surrounding tbe mouths with a sieve or net- work of iron wire (as i 
the case in some of Fletcher's apparatus) are thoroughly unsatisfactory 
These sieves obstruct the blast and are not as much a safeguard again^ 
back explosions as is necessary in an apparatus, where constancy, or a 
least very uni?orm variation of temperature, is the requisite. In th 
blower of Fig. 37 the blast tube h h extends to within an inch of the moutS 
of the burner. The column of gas surrounds this tube. With the fuj 
current of air sent through the furnace the gas may therefore be a 
nearly cut off as is at all desirable, or it may be quite cut off withon 
incurring any risk of explosion, either in the blower or in the burne] 
I may add that the tubes c c and & & for gas supply should both pohj 
toward the more accessible side of the furnace, and there coinmiiiiicatj 
with graduated stop-cocks, such as are furnished by the Buffalo Dents 
Company. For the furnace above half-inch supply-cocks are sufficienl 
The centrifugal blower which I used was of rather a smaller form thanl 
usual in tbe market, being only about eleven inches in diameter and whj 
paddles scarcely two and a half inches wide. It was taken from a porl 
able forge. Doubtless even a smaller blower, i. e., a narrower blowei 
would have been desirable, so that the power of the engine may b 
spent in furnishing pressure of blast rather than quantity of air. Th 
smallest form of Boot blower (blacksmith's model) and larger forms! 
centrifugal blower had therefore to be discarded, for with the availabl 
power the blast obtained proved to be too large in quantity and ta 
small in intensity. In the Boot blower, moreover, tbe flame obtains 
(83G) 
