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DYEING AND CALICO PRINTING .

a red flocculent matter is separated, which, on being collected on a filter, iswashed, dried, and next exhausted with boiling alcohol. This solution isevaporated to dryness, and the residue being again treated with alcohol yieldsa beautiful red semi-fluid substance (erythroleine), soluble in ammonia, witha purplish colour. There is besides dissolved in the alcohol another deep redmatter, soluble in ether, and exhibiting a crystalline structure, forming a bluecompound with potassa, and with ammonia a blue but insoluble substance(erythrolitmine). There remains after the first-mentioned treatment withalcohol a brownish red, amorphous body, insoluble in alcohol and ether, butsoluble in water. It forms with ammonia and the alkalies blue solutions.This is the most important constituent of litmus, being the material which inthe state of a blue potassa salt is dissolved in water, when the litmus ofcommerce is treated with that liquid. The body has been named by Dr.Kane, azolitmine, and contains nitrogen, which is not present in erythroleineand erythrolitmine. According to the author just named, the composition ofazolitmine is C 7 H 7 N0 4 , its formation from orcine being according to thefollowing formula: C 7 H60 2 + NH 3 -l-06 = C 7 H 7 N0 4 -f-H20. The adtion ofcarbonate of potassa produces a more energetic oxidation of the orcine.

Dr. Gelis first exhausts litmus with boiling water; the residue is boiledwith a weak solution of potassa. Both liquids are then mixed and pre-ciptated with subacetate of lead. The precipitate, after having been wellwashed and suspended in water, is decomposed by sulphuretted hydrogen;the ensuing precipitate of sulphide of lead containing the colouring matteris exhausted with an ammoniacal water. This solution being adted upon byhydrochloric acid yields a flocculent precipitate of colouring matter, a smallportion of which remains in solution. This flocculent matter being treatedwith ether yields a red, somewhat crystalline body, soluble in alkalineliquids, with a violet colour. The residue insoluble in ether, being treatedwith alcohol, yields a blood-red solution, which, when evaporated to dryness,leaves a purplish red body with a golden refledtion, the main coloured con-stituent of litmus. There remains, moreover, a body insoluble in water,alcohol, and ether, but soluble in alkalies. From this account it is sufficientlyclear that the chemical history of litmus is far from complete.

What is known as tourncsol en drapeaux , litmus on rags, is almost solely usedin Holland to impart to the outer crusts of cheese a red stain, which preservesit to some extent from decay and from the attacks of inserts. It is a colouringmatter obtained from a kind of euphorbiaceous plant, the Croton tinctorium ,purposely cultivated chiefly at Grand-Gallargues, Departement du Gard,France. The juice of the fruits, berries, and the young top shoots ofthis plant is squeezed out, and clean coarse linen or other rags are steepedtherein. When dry the rags are hung up in or over vessels partly filledwith stale human urine, to which alum and lime have been added, orthe rags are simply covered with horse-dung; this operation is locallytermed aluminadou. The rags are inspected, and the adtion of the am-moniacal vapours carefully watched, because excess of that adtion woulddestroy the colour. They are next dried, and are steeped a second time inthe juice of the plant, but now mixed with urine, after which they are againdried in the sun, and exposed as much as possible to wind. The researchesof Dr. Joly,* of Toulouse, have proved that the colouring principle of the

* Joly, “ Ann. de Chim. et de Phys.” [3], vi., in.