1817.] Collet-Descotils. 419 
new metal, remarkable for the variety of colours which its combina- 
tions assume, and they would be sufficient alone to transmit the 
name of Descotils to posterity. 
In the Memoirs of the Society of Arcueil (i. 370) Descotils has 
given a note on the purification of platinum, which has contributed 
to lower the price of this precious metal. He propases to begin by 
alloying crude platina with zinc, and to digest the alloy in a state of 
powder in sulphuric acid to separate the zinc. The platinum then 
dissolves very readily in aqua regia. It presents the remarkable 
property of burning at a very gentle heat, and even of detonating 
like gunpowder when the proportion of zine employed has not been 
considerable. 
Mr. Chenevix had observed that platinum, precipitated from its 
solution by nitrate of mercury, and reduced in a crucible with a 
little borax, gives a well-fused button of metal about 17 times 
heavier than water. Descotils, on repeating this experiment, ob- 
served that platinum may be fused by means of borax without the 
assistance of mercury, and that, when it was dissolved in acids, 
boracic acid was obtained. This fusible platinum is a true boruret, 
very brittle, and having a crystalline texture. Other metals fused 
with borax presented the same phenomena as platinum. Hence we 
ought to consider Descotils as the first person that formed borurets, 
While making these experiments on platinum, he observed that 
charcoal likewise has the property of combining with platinum in 
the proportion of two or three per cent., and of diminishing its 
density. (Ann. de Chim. Ixvii. 86.) 
We were ignorant of the cause of the infusibility of some varieties 
of sparry iron ore, and of the theory of the processes put in prac- 
tice to render them fusible. Descotils showed by an exact analysis 
that sparry iron ore is not always the same, and that the refractory 
quality of some varieties of it is owing to the great proportion of 
Magnesia which they contain. When these last are left for a long 
time exposed to the air, either before or after being roasted, sulphate 
of iron is formed, the acid of which combines with the magnesia, 
and the new formed salt is washed away by the rain-water to which 
the ore is exposed. From this theory he advised, in order to acce- 
lerate the separation of the magnesia, to water the heaps of roasted 
‘ore with water holding sulphate of iron in solution, a salt which 
may be easily procured by gently roasting, and then exposing to the 
air the pyrites which usually accompany sparry iron ore. ‘The 
‘advantages of this mode are obvious, as it enables us to remove the 
> in a much shorter time than usual. (Jour. de Min. xxi. 
277. 
There exist certain kinds of iron ore, which different mineralo- 
gists have united under the name of clay-iron-stone. Descotils has 
proved that this ore is an earthy carbonate of iron, the situation of 
which is remarkable, as it almost always accompanies coal, and as 
in the places where it occurs alone the beds possess the characters of 
2p 2 
