for meafurirg the higher Degrees of Heat , &c. 319 
Mr. alchorne has been fo obliging as to try the neceffary 
experiments with the pure metals at the Tower, to afeertain at 
what degrees of this thermometer they go into fnfion ; and it 
appears, that Swedifh copper melts at 27? filver at 28, and 
gold at 32. 
Brafs is in fufion at 21. Neverthelefs, in the brafs and cop- 
per founderies, the workmen carry their fires to 140 ana up - 
wards : for what purpofe they fo far exceed the melting heat, 
or whether fo great an additional heat be really necehaiy, 1 
have not learnt. 
The welding heat of iron is from 90 to 95 ; and the greatefb 
heat that could be produced in a common fmith’s forge 125. 
Caff iron was found to melt at 130°, both in a crucible in my 
own furnace, and at the foundery ; but could not be brought into 
fufion in the fmith’s forge, though that heat is only 5 0 lower. 
The heat by which iron is run down among the fuel for calling 
is 150°. 
As the welding {fate of iron is a foftening or beginning 
fufion of the furface, it has been generally thought that call 
iron would melt with much lefs heat than what is neceflary foi 
producing this effedl upon the forged; whereas, on the con- 
trary, call iron appears to require, for its fufion, a heat exceed- 
ing the welding heat 35 or 40°, which is much more than the 
heat of melted copper exceeds the lowefi vilible rednefs. 
Thus we find, that though the heat for melting copper is by 
fome called a white heat, it is only 2 f of this thermometer. 
The welding heat of iron, or qo% is likewife a white heat; 
even 1 30°, at which call iron is in fufion, is no more than a- 
white heat ; and fo on to 1 6o° and upwards is all a white heat 
{fill. This {hews abundantly how vague fuch a denomination muff 
be,, and how inadequate to the purpofe of giving us any clear 
ideas- 
