FOR MEASURING THE EXPANSION OF SOLIDS. 
283 
an inch of the same end was found to have been converted into steel, but all 
the rest retained the character of soft iron. 
Exp. 20. I repeated the last experiment with the same platinum bar in the 
register I. The arrangement was precisely the same, with the exception of 
the second register with the iron bar, and the fire was maintained with equal 
intensity for an equal time. 
The iron nails were found perfectly melted, and the porcelain superficially 
fused as before. The ring and wedge, however, were fixed in their places, and 
the index undisturbed, but the measure was unfortunately lost from an acci- 
dent. The texture of the platinum ring was changed, as in the previous expe- 
riment, and the bar tightly fixed in the cavity. By frequent gentle concussions 
it was removed without injury to the black-lead, which had some slight marks 
of fusion upon its surface, but was in a perfectly good condition. The bar was 
in a still rougher state than before, highly crystalline, and exhibited several 
large longitudinal clefts in its substance. It was found, by measurement with 
callipers, to be |>th of an inch larger in diameter at its lower than at its upper 
end, and seemed to be approaching a state of complete disintegration. It was, 
however, perfectly hard and inflexible. My intention was to have again exposed 
it for several hours to the same degree of heat, with the expectation that the 
disintegration would have been complete, and that it would actually have 
fallen in pieces during the operation : in the mean time I chanced to make it 
red hot upon a common charcoal fire ; and upon attempting to lay hold of it 
with a pair of tongs the two ends dropped off, and I only withdrew the small 
portion which I had grasped, and which was flattened and fractured by even 
this slight compression. The two ends were afterwards carefully, but with 
difficulty, raised from the fire, and when cold were perfectly hard and inflex- 
ible. I again heated a portion of the bar to a dull red, and it crumbled to 
powder from a slight blow with a hammer. 
Exp. 21. It being a point of the greatest interest to ascertain the maximum 
of expansion which took place in the platinum previous to this remarkable 
change of structure, I adjusted the original platinum bar, with which the 
greater part of my experiments had been made, and which presented a per- 
fectly smooth surface, and was very soft and ductile, in the register I. A cru- 
cible was placed in the same wind-furnace, containing only a little charcoal 
