A Comprehensive Treatise on Inorganic and Theoretical Chemistry

402 INORGANIC AND THEORETICAL CHEMISTRY
Some sulphates of what is regarded as tervalent platinum have been investigated.
They are here called the platinosic sulphates. M. Delepine reported that a platinosic
dihydroxyhydrosulphate, Pt(OH)2(HSO4).H2O, can be obtained by boiling platinum
with sulphuric acid for a long time when the liquid gradually darkens in colour
until finally, after 30 hrs., it becomes almost black when it contains about 20 grms.
of platinum per litre. The soln. can be diluted with water, or it can be evaporated
to dryness, the residue taken up with water, and when the soln. is treated with half its
vol. of cone, sulphuric acid, it furnishes black plates. Since at 100° this compound
loses 1*5 mols. of water per atom of platinum, it might be represented by the
formula 0{Pt(OH)(HS04)}2.3H20 ; and since it can be converted into an equimolar
mixture of H2PtCl4 and H2PtCl6, it was inferred that the platinum in the compound
is tervalent. The compound crystallizes from aq. soln. in black, rectangular prisms.
The compound is extremely soluble in water, cone, sulphuric acid, acetic acid,
alcohol, and acetone forming reddish-brown soln. with ether it forms a compound
containing 2 mols. of ether, which is insoluble in ether. Alkali lye precipitates
from the soln. a dark brown oxide.
According to M. Blondel, platinosic hydroxydihydrosulphate, Pt(OH)(HSO4)2.
9|H20, can be represented as Pt2(0H)6(S03)4(0H)2.8£H20, and L.. Wohler and
W. Frey consider it to be a hydrosulphatoplatinosic acid analogous to hydrochloroplatinic
acid. M. Blondel, and M. Delepine showed that when platinum
dissolves in boiling sulphuric acid in an atm. of carbon dioxide, the reaction
2Pt4-7H2S04^3S02+4H204-2(HO)Pt(HS04)2, is reversible ; when air was used,
twice as much platinum 'dissolved, and less sulphur dioxide was evolved, owing to
the oxidation of the sulphur dioxide to trioxide under the influence of the platinum.
With oxygen, four times as much platinum dissolved, and less still sulphur dioxide
was evolved. When a mixture of carbon and sulphur dioxides was used, no soln.
of platinum took place, and, in some cases, platinum was precipitated from soln.
M. Blondel observed that in J. J. Berzelius' process for preparing platinic sulphate,
this compound is in part obtained because platinic oxide is slowly reduced to
platinosic oxide at about 110°. E. Prost reported that Pt8O13SO4.16H2O is precipitated
when a soln. of platinic sulphate, free from nitric acid, is boiled.
M. Blondel prepared this compound by reducing a soln. of platinic sulphate in
sulphuric acid by means of oxalic acid, and L. Wohler and W. Frey employed the
same reducing agent. The orange-red prisms or plates were found by M. Blondel
to be triclinic pinacoids with the axial ratios a : b : c—1-6236 : 1 : 0-5492, and
cx=90° 29', £=101° 53', and y=88° 55' ; the (010)-cleavage is complete. The salt
effloresces in dry air, and when dried over sulphuric acid under reduced press., it
forms the stable Pt(OH)(HS04)2. This compound does not change at 110°, but
at 150° it begins to lose sulphur trioxide, and is partially reduced. When exposed
to moist air for some days it forms a gum-like mass. The aq. soln. decomposes
slowly in the cold, and more quickly when heated, forming a brown precipitate
with a variable composition. An excess of hydrochloric acid produces a mixture
of platinous and platinic chlorides. The acid is dibasic. Although the addition
of the eq. of 2 mols. of sodium hydroxide forms a crystallizable sodium salt, more
alkali can be added because the salt is gradually polymerized with the liberation
of acid in a colloidal form. When an excess of the alkali lye is added to a boiling
soln., a polymerized form of platinum sesquioxide is precipitated. Sodium, potassium,
and barium hydroxides and the oxides of thallium, iron, and silver form
crystallizable salts. Aq. soln. of the acid give no precipitate at first with barium
chloride, but they do so after standing some time. This acid therefore has some
analogies with the complex sulphates of iron and chromium studied by A. Recoura.
Li. Wohler and W. Frey found that the titration with a soln. of potassium permanganate
agrees with the assumption that the compound contains tervalent platinum.
The platinic dihydroxyhexammino-/A-aminodisulphate, [(OH)(NHg)3Pt(NH2)-
Pt(NH3)3(OH)J(S04)2 of P. T. Cleve, obtained in snow-white needles by the action
of dil. sulphuric acid on the corresponding nitrate, has been regarded as platinosic