200 Mr. Daniell on a New Register- Pifvometer 



termination of the total expansion to the fusing points, to 

 determine previously the expansion of each to the points of 

 boiling water and boiling mercury; that any alteration in the 

 rates of expansion between these points might be detected. 



I must, however, make a few observations upon the general 

 method which 1 adopted to insure an accurate determination 

 of the former. 



Exp. 26. — Judging from the action of the pyrometer at 

 lower heats, I expected that the index would continue to be 

 thrust forward by the progressive expansion of any bar of 

 metal, till its cohesion gave way and it assumed the fluid form ; 

 and consequently that a register would be obtained of its maxi- 

 mum dilatation : but the difficulty consisted in applying the 

 heat so equally that one part should not melt before another. 

 The arrangement which I finally adopted to secure this pur- 

 pose, and which was found to answer perfectly, was as follows. 

 In the laboratory of the Royal Institution there is an excellent 

 wind-furnance, from which proceeds a lateral horizontal flue, 

 along which a flame may be drawn with any recjuired degree 

 of force. Into this flue open two muffle-holes, which give a 

 complete view and command of the interior. From the equa- 

 lity of the draught, regulated by a register, the whole of this 

 chamber may be kept at a low red, or an intense white, heat, 

 by a proper management of the fuel in the body of the fur- 

 nace. 



The registers of the pyrometer were prepared for the ex- 

 periment by drilling three holes on their under sides, commu- 

 nicating with the cavities in which the bars were placed ; one 

 at each extremity, and one in the centre. This was done for 

 the purpose of allowing a vent for the melted metal, and to af- 

 ford some criterion of the equality of the heat, by the time at 

 which the metal ran from the different apertures. When the bar 

 was properly adjusted in the register, it was carefully placed in 

 the hot air-chamber, in a horizontal position, supported at each 

 end by a small i)iece of brick, at a proper distance from the 

 body of the fuel, accordingly as a greater or less degree of 

 heat was required. The muffle-holes were then closed with 

 their stoppers; all but a narrow slit, through which the pro- 

 gress of the heating and the flow of the metal could be ob- 

 served. The e(|uality of the heat could be very accurately 

 ascertained by the uniform colour of the register as it became 

 red; and any irregularity could easily be corrected by ad- 

 vancing one or other end more towards the fuel. In this 

 manner I succeeded in obtaining very satisfactory results; 

 except in the case of gold ; and this metal requiring for its 

 fusion rather more heat than I could at the time command in 



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