Mars Marrone

: ON THE SEMI-NEUTRAL, GRAY.

Under the heading of a New Marrone Pigment there appeared some months

back in a chemical journal the following:--"The blood-red compound

obtained by adding a soluble sulphocyanide to a salt of iron in solution

can be made (apparently at least) to combine with resin thus: To a

concentrated solution of sesquichloride of iron and sulphocyanide of

potassium in ether, an etherial solution of common resin is added, and

the w ole well shaken together. There is then mixed with it a

sufficiency of water to cause a precipitate, when it will be found,

after the mixture has stood a few hours, that the whole or nearly the

whole of the red-coloured iron compound has united with the precipitated

resin, forming the marrone-coloured pigment in question. When this

coloured substance is finely powdered and mixed with water, the liquid

is not the least coloured; whence it is inferred that the red iron

compound has chemically united itself with the resin."



The foregoing account is rather to be regarded as of scientific interest

than of practical utility. The blood-red solution of sulphocyanide of

iron is in itself not stable: when the red solution of this salt is so

exposed to the sun, that the rays pass through the glass jar containing

it, it is rendered colourless, but the colour is retained or restored

when the rays pass directly from the air into the fluid; so that when a

properly diluted solution is placed in a cylindrical glass vessel in

direct sunshine, it loses colour in the morning till about eleven in the

forenoon, when the rays beginning to fall upon the surface exposed to

the air, gradually restore the colour, which attains its maximum about

two o'clock. Moreover, the solution is immediately decolourised by

sulphuretted hydrogen and other deoxidizing agents, as well as by

alkalies and many acids. It is scarcely probable that the union of the

red colouring matter with the resin would suffice to secure it from

change; and there is little doubt that the new marrone pigment would be

a chameleon colour.



* * * * *



Failures in the process of burning carmines, and preparing the purple of

gold, frequently afford good marrones. Compounds more or less of that

hue are likewise furnished by copper, mercury, &c. Some ochres incline

to marrone when calcined: indeed we have remarked in many instances that

the action of fire anticipates the effects of long continued time; and

that several of the primary and secondary colours may, by different

degrees of burning, be converted into their analogous secondary,

tertiary, or semi-neutral colours.



The one marrone or brown-marrone pigment at present employed, brown

madder, is permanent.












TTITLE SEMI NEUTRAL GRAY



Of the tribe of semi-neutral colours, GRAY is third and last, being

nearest in relation to black. In its common acceptation, and that in

which we here use it, gray, as was observed in the third chapter,

denotes a class of cool cinereous colours faint of hue; whence we have

blue grays, olive grays, green grays, purple grays, and grays of all

hues, in which blue predominates; but no yellow or red grays, the

prevalence of such hues carrying the compounds into the classes of brown

and marrone, of which gray is the natural opposite. In this sense the