Obfervations on Platind. 1H 
~ The account of eafe-hardening is very unfatisfatory ; and 
although the analogy betwixt it and the cementing of fteél 
be preat, yet it would puzzle any one to make bar ftecl from 
iron by following the procefs deferibed ; and ftill more to 
produce bar fteel from caft-iron, by cementing it in the 
manner mentioned by Mr. Collier. 
T hope Mr. Collier will not feel offended by the freedom 
with which I have examined his obfervations. Great are the 
improvements withed for, and expected, in the manufa@ur- 
ing of iron; and it is only by numerous experiments, and 
‘liberal difcuffions on the fubject, that thefe great defiderata 
are to be obtained. 
Ill, Obferuations on Platina, and its Utility in the Arts, toge- 
ther with fome Remarks on the Advantages which refletting 
have over achromatic Telefcopes. By ALEXIS Rocyon, 
Direstor of the Marine Objervatory at Breft, From the 
~ Journal de Phyfique, 1798. 
P LATINA isa metal exceedingly refractory, unchange- 
able, very compaét, and capable of receiving a fine polith. 
This fingular metal has never yet been found but in the gold 
mines of Choco. The Spaniards gave it the name of juan 
blanca, that is to fay white gold, and platino del Pinto, which 
fignifies little filver of Pinto. It is brought to us from Choco, 
under the form of triangular grains the angles of which are 
rounded. Thefe grains are irregular, du@tile, and fufceptible 
of being attraéted by the loaditone. It is never pure, and 
always contains a black fhining fand, over which an artifi- 
cial magnet has great power. This {and is interfperfed with 
_ gold grains and fragments of fmall coloured cryftals. The 
fpecific gravity of platina is to that of gold as 22 to 19}*. 
Like that precious metal, it refifts the ation of fimple acids, 
* We have feen fome platina where the difference was ftill greater. EIT. 
C2 and 
