APPENDIX TO TABLE FOR THE ANALYSIS OF GROUP II.,

Exhibiting the general outline of the method of dealing with the metals Pd, Ir, R, Ru, and Os, which, together with some Fe and Cu, are found in platinum ore.

The mineralis dissolved in a retort by means of a mixture of 5 parts of the most concentrated HCI with 1 part of fuming HNO3, and the acid which distils over as the liquid boils, collected in a receiver; the distillate is returned and redistilled.

The distillate will contain the Os as Os2 O Saturate with solution of KHO; add EHO, and warm gently, when a fine red crystalline precipitate forms, which is KOSO2.

The syrupy residue in the retort is then filtered off from certain dark steel-coloured grains, which are not acted upon by the acid.

The insoluble grains are called Osm-iridium, and contain Os,

Ir, and Ru. These are powdered in a steel mortar, and fused with a

mixture of equal parts of KHO

and KCIO. The mass is treated with water.

The concentrated filtrate is mixed with about twice its

bulk of EHO, and then with a warm solution of KC until no more precipitate is formed. It should be allowed to rest for some time, filtered, and washed with weak EHO containing KCl.

The yellow or
red crystalline
precipitate con-
sists of KPtCl
and KIrCl3,
with traces of
K2 R2 Cl, and
KPdCl2.
It is gently
heated with an
equal weight of
Na2CO3 in a
porcelain cru-
cible until the
mass becomes
quite black. It is
then boiled with

water acidified with HCl, and the residual black powder of Pt and Ir2 O washed. It is then digested with dilute nitrohydrochloric acid, in order to extract part of the Pt; and this solution being preserved, the insoluble residue of Pt (yet undissolved) and Ir, O is mixed with NaCl and concentrated nitrohydrochloric acid, and evaporated to dryness. Water is then added, to dissolve the PtCl2, and the solution filtered, the filter being washed with NaCl solution, and finally with NH4Cl, to prevent the Ir2O passing through the pores of the paper.

The examination for acid-radicals is to be conducted in accordance with the plans given on pp. 413, 414.

Suitable mixtures for analysis may easily be made. For instance, at first two salts should be taken containing a common acid-radical and different basic radicals belonging to different groups; then a mixture may be made, the basic constituents of which are four in number, two belonging to one group, and two to another. The student should then exercise himself in effecting the more difficult and delicate methods of separation, gradually increasing the number and variety of the basic and acid-radicals to be detected. Trials should also be made with mixtures of soluble and insoluble salts, with alloys, with salts incapable of remaining dissolved in the same solution, and with some of the substances met with in commerce or in common life.