Citrine Brown

: ON THE TERTIARY, RUSSET.

From boiling, hot, or cold solutions of bichromate of potash and

hyposulphite of soda in excess, we have obtained an agreeable

citrine-brown colour, varying in hue and tint according to the mode of

preparation and proportions of materials employed. It is a hydrated

oxide of chromium which, when washed and carefully dried, yields a soft

floury powder. Transparent, and affording clear, delicate pale washes,

the oxide has not been introduced as a pigment; partly owing to certain

physical objections, and partly to a tendency to greenness. This

tendency is peculiar to all the brown chrome oxides of whatever hue,

whether hydrated or anhydrous; and indeed distinguishes more or less

nearly all the compounds of chromium. Green, in fact, is the natural

colour of such compounds, the colour which they are constantly

struggling to attain; and hence it is that the green oxides of chromium,

being clothed in their native hue, are of such strict stability. The

inclination to green which the citrine under notice possesses, may be

seen by washing the precipitate with boiling water. It has been

supposed that hydrated brown oxide of chromium is not a distinct

compound of chromium and oxygen, but a feeble union of the green oxide

with chromic acid. If this be the case, the citrine cast of the brown

oxide is easily explained, as well as the gradual addition to its green

by the deoxidation of the chromic acid.



In mixed tints for autumn foliage and the like, the tendency to green of

this citrine brown would be comparatively unimportant; but whether the

oxide be adapted to the palette or not, we believe the colour might be

utilized. In dyeing, for instance, the solutions of bichromate of potash

and hyposulphite of soda would be worth a trial, the liquids of course

being kept separate, and the brown washed with cold water. Various

patterns could be printed with the bichromate on a ground previously

treated with hyposulphite.



* * * * *



Several other browns, and ochrous earths, partake of a citrine hue, such

as Cassel Earth, Bistre, &c. But in the confusion of names, infinity of

tones and tints, and variations of individual pigments, it is impossible

to arrive at an unexceptionable or universally satisfactory arrangement.

We have therefore followed a middle and general course in distributing

pigments under their proper heads.



Of the three citrines in common use, Mars brown and raw umber are

strictly stable; while brown pink, the purest original citrine the

palette possesses, is either semi-stable or fugitive, according to the

colouring substance used in its preparation.










TTITLE TERTIARY RUSSET





Russet, the second or middle tertiary colour, is, like citrine,

constituted ultimately of the three primaries, red, yellow, and blue;

but with this difference--instead of yellow as in citrine, the archeus

or predominating colour in russet is red, to which yellow and blue are