Emnuicaty Nous, } History of the Oxides of Manganese. 137
ee ees ee —————O te tr. ————— — ——— — mm ——————, rested
ymmonio-magnesium arsenate from which the percentage flask was now boiled, and yielded, after three-quarters of
of arsenic is calculated. an hour, about .3 c.c, of gas, the precipitate at the same
Analyses made bythe method last described have given time becoming quite black. This gas was certainly not
very good results. Amongst several analyses made by pure oxygen, and as an equal bulk of the distilled water
this method may be mentioned the following :—Two ised in making the solutions yielded, on boiling for the
mixtures of 100 grains of copper and o'25 grain each of 3ame length of time, about the same quantity of gas, there
antimony, lead, bismuth, tin, and iron, to which o's grain seems no reasonable doubt that in both cases the gas was
and o'r grain of arsenic respectively had been added, air dissolved in the water, or which had diffused into the
yielded 0°48 grain and o'10 grain of arsenic respectively. apparatus.
My thanks are due to my assistant, Mr. H. A. Kay, The experiment was next repeated, the flask this time
who has made most of the required analyses, and who has Jeing filled with a solution of about 5 grms. of permanotherwise
 given much valuable help in carrying out this zanate, and 1'02 grms. of the manganous sulphate was
investigation. jissolved in water, and run into it, The same brown
i Contributions to the History of the Oxides of Man. precipitate was observed, but again no gas was given off
ganese.” By J. T. Dunn, M.Sc. Wishing to determine in the cold. On boiling a slow evolution of gas took
sulphurous acid dissolved in oil of vitriol, and casting solace, which ceased after about an hour, during which
about for a method which would not involve the use of ‘ime about 200 c.c. was colleGed. A lighted match
such large bulks of air-free water as are necessary for showed that the gas contained a large quantity of oxygen,
accuracy in titrating with iodine, I tried, amongst other and absorption of a sample by phosphorus showed that
things, solution of permanganate of potassium. I pro- it was practically pure.
nosed to sink the measured quantity of SOz solution A blank experiment, made for precaution’s sake, in
nder excess of standard permanganate solution, and to which the same quautity of permanganate solution was
determine the amount of oxygen used up by excess of ooiled for an hour, without addition of manganous
standard ferrous sulphate solution and back titration with sulphate, and in which only 7 c.c. of gas was given off,
permanganate. Of course, on adding the SO, to excess showed that the gas in the last experiment did not come
of permanganate, a quantity of brown hydrated oxide of from the simple breaking up of the permanganate by heat.
manganese is precipitated, but addition of acidified The experiment was repeated with the same quantities
‘errous sulphate, as is well known, easily reduces and >f the materials, and they were left together in the cold for
dissolves this oxide. five days. No gas was collected in the measuring tube,
It had long been well known that the precipitates pro- out a few minute bubbles appeared hanging on to the
luced by the action of reducing agents on excess of per- precipitate.
manganate, as well as those formed by acing with alkalies It seems, then, that when solutions of permanganate
and oxidising agents on manganous salts, have not, as a ind manganous sulphate are mixed, no evolution (practitule,
 the composition of manganese dioxide, but contain a ally) of gas takes place in the cold, and that, on heating,
sercentage of oxygen falling short more or less of that oxygen is evolved when the permanganate is in excess,
required for the formula MnO, Mr. Francis Jones states but not when the manganous salt is in large excess. I
(our. Chem. Soc., 1878, page os) that he has observed next tried to ascertain whether the action was a deteran
 evolution of oxygen gas in all cases of the action of minate one, or whether, as seemed possible, it was an
reducing agents on permanganate which he has examined, :xample of so-called © catalytic” action—whether the
although he gives us no figures, nor any guide whatever precipitated oxide acted towards the excess of permangaas
 to the amount of gas which he has so noticed. So 1ate in the way that cobaltic hydrate does towards
far as I am aware, no other author who has experimented »oleaching-powder in Fleitmann’s method o preparing
with oxides of manganese makes any mention of oxygen OJxygen.
being given off under these circumstances; but a possible A small quantity of the moist precipitated hydrate from
:onnection between the evolution of oxygen and the :he last experiment, which had been washed in the cold
deficiency in oxygen below the formula MnO, exhibited till free from adhering permanganate, was placed in the
hy the precipitated oxides, at once suggests itself. Jask, which was then filled with permanganate solution
In my work with sulphurous acid, since it wasnecessary, about 5grms. of the salt). The precipitate and the fluid
in order to insure the complete diffusion of the saturated were then boiled together, but, after two hours, only about
acid out of the narrow-necked little bottle in which it was 20 c.c. of gas had colleGted, which was found to be
weighed, to permit the permanganate solution under oxygen. Again, the flask was filled with the same
which it was sunk to stand over night, it is evident that juantity of permanganate, and a solution of o'25 grm.
any such evolution of oxygen as that mentioned by Jones, of manganous sulphate added, and boiled; 46 c.c. of gas
gven if it took place very slowly, would have rendered the was coile@ed, and shown to be oxygen; and it will be
jeterminations useless. 1 endeavoured, therefore, to noticed that the quantity bears roughly the same ratio to
‘epeat some of Mr. Jones's experiments under determinate :he 200 c.c. collected in a former experiment that the
sonditions, to ascertain whether, under these conditions, manganous sulphate used here does to that used in the
evolution of oxygen did take place, and, if so, to what other case.
extent, 1 afterwards, for other reasons, abandoned the The reaction was then apparently definite, and it seemed
use of permanganate in favour of bichromate; but the worth while, if possible, to put it on a quantitative basis.
cesults of the few experiments which I made are perhaps Decinormal solutions of permanganate and of manganous
worth while putting on record. sulphate were prepared, containing 3°16 grms. and 1°51
A small flask was taken, fitted with a two-holed cork, zrms. of the salts respedively per litre. (The permangathrough
 which passed a gas-delivery tube and the tube of nate was rather above decinormal strength, 100 c.C. being
a stoppered funnel, the latter reaching to the bottom of squivalent to 00°4 C.C. decinormal solution.)
the flask, Flask and delivery tube were completely filled Into the flask was introduced 100 c.c. (=100¢) perwith
 a solution of about 15 grms. of manganous sulphate manganate solution, and the air was then displaced by a
(the same sulphate was used in all the experiments, and stream of CO,; 100 c.c. of MnSOy, solution was added
contained 11°32 per cent of water), and a solution of 0'63 through the funnel tube without introducing air, and the
grm. of permanganate, in a small quantity of water, was liquid and precipitate boiled together for two hours, the
added through the funnel tube without admitting any air, gas given off being collected over caustic soda. After
the delivery tube of the flask dipping under water, and allowing for the small quantity of residual air in the flask,
having a graduated tube filled with water inverted over it. 23 c.C. of oxygen remained. The contents of the flask
Immediately on the introduction of the permanganate a were poured on an asbestos filter, and the precipitate
brown flocculent precipitate formed, but, after half an washed. The filtrate was perfectly colourless, and hence
nour, there was no evolution of gas. The fluid in the contained no permanganate. It gave no precipitate with