; 3 20 An Attempt to make a Thermometer 
ideas or the extent of what we have been accuffomed to con- 
iider as one of the three divifions of heat in ignited bodies. 
A Hefiian crucible, in the iron foundery, viz* about i ^o°, 
melted into a flag-like fu bifan ce. Soft iron nails, in a Hef- 
lian crucible in my own furnace, melted into one mafs with 
the bottom of the crucible, at 154 0 : the part of the crucible 
above the iron was little injured. 
Th e finding heat of the glafs furnaces I examined, or that by 
which the pei fe£t vitrification of the materials is produced, was 
at one of them 1 1 4 0 for flint-glafs, and 124° for plate-glafs ; 
at another it was only yo° for the former, which Ihews the 
inequality of heat, perhaps unknown to the workmen them- 
felves, made ule of for the lame purpofe. After complete 
vitrification, the heat is abated for fome hours to 28 or 29°, 
which is called the fettling heat ; and this heat is fufficient for 
keeping the glals in fufion. The fire is afterwards increafed, 
for working the glals, to what is called the working heat; and 
this I found, in plate-glafs, to be 57 0 . 
Delft waie is fired by a heat of 40 or 41 0 ; cream-coloured, 
or Queen’s ware, by 86° ; and Hone ware, called by the French 
pots de gres , by 102°: by this ftrong heat, it is changed to a 
true porcelain texture. The thermometer-pieces begin to 
acquire a porcelain texture about no°. 
The above degrees of heat were afcertained by thermometer- 
pieces fired along with the ware in the refpeftive kilns. But 
tins thermometer affords means of doing much more, and 
going funner in thefe meafures than I could at firft even have 
expedfed ; it will enable us to alcertain the heats by which 
many of tne porcelains and earthen wares of diffant nations 
and different ages have been fired : for as burnt clay, and com- 
petitions in which clay is a prevailing ingredient, fuffer no 
diminution 
