MANUFACTURE OF GLASS FOR OPTICAL PURPOSES. 
57 
alloyed parts, if any such are adhering to it, and then digested in a Florence 
flask, with a mixture of five measures of strong muriatic, one measure of 
strong nitric acid, and three measures of water. But little heat should be 
applied at first until the action diminishes. According to Dr. Wollaston, one 
ounce of platina will be dissolved by about four ounce measures of such acid, 
and it is advantageous to have a considerable excess of platina present. The 
solution obtained is to be precipitated by a strong solution of muriate of am- 
monia ; a bright yellow pulverulent substance will fall, and a mother liquid 
having more or less colour remain. The precipitate being allowed to subside, 
the liquor is to be poured off, and the former then washed with two or three 
portions of water. The washing liquors and the mother water may afterwards 
be concentrated together ; but it is better not to prepare spongy platina for 
this particular use from these fluids, but only from the precipitate which falls 
on adding the muriate of ammonia. 
The yellow precipitate, when washed, is to be dried on a filter, or in a basin, 
and then decomposed by the application of a dull red heat. This may be 
done in a clean white earthenware crucible. The heat should be continued 
until vapours cease to arise ; but this will be found a long operation, in con- 
sequence of the low temperature which is to be applied, and the exceeding- 
bad conducting power of platina for heat when in this spongy state. The 
reduction may also be performed by putting the precipitate upon a piece of 
platina foil in a layer about -Lth of an inch in thickness, and covering it with 
another piece of foil ; a spirit lamp will then suffice to reduce the metal, but 
the foil and powder must be turned occasionally, that both sides may be ex- 
posed to the flame. The platina will appear as a dull grey spongy metallic 
mass. It should be broken up, mingled, and then again heated to insure the 
dissipation of all volatile matter. 
After this is done, the platina should be rubbed to powder by the clean 
finger, or clean paper (83), heated slightly a third time, and then preserved 
in a clean and well stoppered bottle. 
MDCCCXXX. 
I 
