DE. JOrLE ON SOME THEEMO-DYNAMIC PEOPEETIES OF SOLIDS. 
95 
occupied, might be got rid of by the following arrangement : — A rim a, fig. 4, contains 
pitch or other cement to secure the joint between the 
chimney and top plate glass ; a rim at h contains pitch 
to secure the orifices where the wires pass through 
the top plate. The bottom of the chimney rests upon 
a round metallic plate, into which a metal pipe c is 
screwed, which is attached by india-rubber tube to the 
glass tube d. This tube is hermetically sealed after the 
air of the receiver has been exhausted through it. All 
the lower joints are then rendered permanently tight, by 
putting the instrument in the shallow dish e filled with L 
melted pitch. 
Thermo-electricity of Iron in different states. 
13. In my earliest experiments on the thermal etfect of stretching a steel bar, I 
placed a copper wu'e in contact with the steel, and completed the circuit by an iron whe 
in contact with another part of the steel bar not under tension. I found anomalous 
results which I was ultimately able to refer to the strong thermo-electric relation 
between hard steel and iron. It was at once obvious that the existence of such maiked 
differences between ferruginous metals in various states of aggregation or purity might 
render the thermo-multiplier a valuable test in the hands of practical men. I theiefoie 
allowed myself to be diverted awhile from the main object of inquiry in the endeavour 
to throw some light on so interesting a question. 
14. Professor Thomson has described^ the changes in thermo-electric position which 
are produced by the various conditions under which metals are placed. He has shown 
that the process of hardening by plunging into cold water brings copper and most other 
metals nearer antimony in the thermo-electric series, but that iron is brought nearer 
bismuth : I find that in steel the change is in the same direction as in iron, but of 
enormously greater magnitude. In a softened state, the position of steel is about 
midway between copper and iron, but after hardening it by plunging it at a brij^ht red 
heat into water, I have in some instances found it to be on the bismuth side of coppei, 
the alteration of the thermo-electric position of the same specimen amounting to as 
much as i^th of the entire range between bismuth and antimony. In all the speci- 
mens of wrought and cast iron I have examined, there is a notable effect in the same 
direction produced by plunging at bright red heat into water; but although a gieat 
change in the molecular state was thus occasioned, evinced by the iron bending with 
twice the difficulty it did when annealed, and the cast iron resisting the action of the 
file, either metal was only brought nearer bismuth by of the inteival between 
bismuth and antimony. A fresh illustration of the extraordinary physical change 
produced in iron by its conversion into steel is thus afforded ; and I believe that the 
* Philosophical Transactions, 1856, Part III. p. 722. 
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