172 Ob/ervations on Platina, 
compofe it are very clofe; but they have only a very feeble’ 
adhefion, like that of an earthen veffel dried in the fhade, 
It is then that the platina muft be expofed to the moft vio- 
lent fire; and when the metal has undergone that operation, 
it reftumes its natural ftate, becomes fonorous, malleable, 
and the ftrongeft heat gives it always new degrees of im- 
provement. 
A little time after I had read this memoir, the learned Dr. 
Ingenhouz begged me to unite into a mafs. for him about 
two ounces of platina, which he had carefully purified by 
means of the nitro-muriatic acid. I was obliged to inclofe 
in a very thin leaf of platina all the fragments of this metal, 
which were too feattered and too minute to be fubjeéted 
feparately to the aétion of the fire and of the ftamper ; 
but, when thus united, I gave them the higheft degree of 
heat poflible to be produced from charcoal excited” by a2’ 
pair of bellows; and I foon ‘obtained, by ftriking them with 
the ftamper, a duétile and malleable mafs. After the fuc- 
cefs of this experiment, I employed myfelf in purifying in 
the fire, and in a crucible, platina in grains, by means of 
‘nitre and fandifer, which muft be afterwards wafhed in the 
nitric acid ; and by ftriking at a white heat thofe grains con- 
tained in the lamine of platina, I procured at a {mall ex- 
pence confiderable maffes of malleable platina. This pro- 
cefs will render unneceffary hereafter the ufe of the oxyd of 
arfenic, unlefs the workman wifhes to obtain, by cafting, 
Jarge crucibles or mufiles of platina. 
~ I was the firft who treated platina in a large mafs in a 
“manner truly ufeful to the arts: and though I have paid a 
‘great deal of attention to this labour, affifted by the informa- 
‘tion'of the learned Ifquierdo and the metallurgic talents of - 
‘Daumy junior, I have employed my chief care in improy- 
ing the mixture of platina with tin and the oxyd of arfenic, 
for the conftrugtion of large fpecula for telefenpes, and, above 
gil, for the fpecula of fextants and other inftruments for de- 
termining 
