4 ,o8 
Dr. Pearson's Observations 
7. The celt. No. 3. after melting — 
Ditto, another piece — 
§ 4. Experiments with Fire. 
8,834 
8,600 
(a) These old instruments melted at a lower temperature 
than that at which copper, or even some kinds of brass melt. 
Although I did not succeed in determining precisely the 
temperature at which each of them fuses ; it may be useful 
to relate the experiment made with that view. 
( b ) 100 grains of each of the above seven ancient metallic 
instruments, and the same quantity of copper, of pure silver, of 
allay of copper with one-eighth of its weight of tin, of allay of 
copper with one-tenth of its weight of tin, of allay of copper 
with one-twentieth of its weight of tin, of allay of three parts 
of copper with one of zinc, and of gun-metal, were exposed 
each in separate coppels, under a muffle, to the greatest degree 
of fire which I could produce in the best assay furnace. 
A pyrometer clay piece of Wedgwood’s instrument was 
also put into each coppel. 
During forty minutes exposure to fire, not one of the metals 
melted, except the pure silver,* and the allay with zinc : nor 
did any of them emit visible vapour, or inflame, except the 
allay with zinc ; nor did any matter ooze out of any of the 
metals. 
* In Wedgwood’s scale it is stated, that pure silver melts at 28°, and Swedish 
copper at 27 0 . But every part of the furnace in the above experiments might noc be of 
the same temperature, for the same space of time : and perhaps the state of cohesion 
and figure of the metal exposed to fire may account for the difference in the degree 
noted by the pyrometer in my experiment, from that stated in the scale. For I am 
assured, by Mr. Thomas Wedgwood, that the degree of contraction is uniform 
among a number of pyrometer pieces, exposed in the same part of the furnace at the 
same time. 
