492 DYEING AND CALICO PRINTING.

with ether; the solution thus obtained yields, on evaporation in vacuo , a porousyellowish mass.

According to Dr. Delfts,* the solution of catechutannic acid becomes, whenexposed to air, deep red, and yields then catechuin; this latter assertion isdenied by M. Neubauer,f who states that the oxidation of the catechuin causedby exposure of its solution to air results in the formation of a tannin pre-cipitable by gelatin.

Alkalies favour the oxidation of the tannin of catechu when in aqueoussolution ; catechutannic acid does not yield glucose when it is boiled withdilute sulphuric acid, and differs in that respett from ordinary tannin, viz.,that of nut-galls.

According to the researches of Dr. Davy and Dr. Nees von Esenbeck, thequantity per cent of catechutannic acid found in the undermentioned varietiesof catechu amounts to :—Bombay cutch, 54*4 ; Bengal, 48*2 ; Gambir, 36 to 40.

Catechuin,J when pure, is a silky crystalline substance, with a peculiarmother-of-pearl-like appearance, containing water of crystallisation, drivenoff at ioo°; fusing at 217 0 , decomposed at a higher temperature, and therebyconverted into a volatile product, pyrocatechuic or oxyphenic acid, C6H6O2.Catechuin is almost devoid of taste, neutral to test-paper; soluble in 1133parts of water at 17 0 , and in from 2 to 3 parts of boiling water, but crystallisingfrom that solution on cooling in acicular-shaped crystals; soluble in from5 to 6 parts of cold, and from 2 to 3 parts of hot, alcohol ; soluble in 120parts of cold, and from 7 to 8 parts of boiling, ether.

Catechuin is best prepared from the yellow catechu met with in cubical-shaped cakes ; this substance, first reduced to powder, is next exhausted withcold water for the purpose of eliminating the tannin ; the residue is thentreated with about eight times its weight of boiling water; the catechuinseparates from this solution after cooling, and the substance is then pressedbetween cloth to separate the mother-liquor; thereupon the crystalline massis re-dissolved in water, and this solution precipitated with subacetate of lead.Care is taken to add this reagent drop by drop, and to stop further addition assoon as a white precipitate begins to appear; the fluid is then filtered, andthe filtrate precipitated with the above reagent. The deposit thus thrown downis washed with some hot distilled water, and next suspended in boilingwater, and decomposed by means of sulphuretted hydrogen. The liquid isagain filtered while yet hot, and on cooling deposits pure catechuin. Thissubstance consists, in the anhydrous state of 61*4 per cent of carbon, and5 per cent of hydrogen, the remainder being oxygen; in the hydrated state itcontains per cent—Carbon, 52*06; hydrogen, 6*o.

In consequence of the importance of catechuin as a dye-stuff, we have toenter into some details here on the different opinions held in reference to thecomposition of this material. M. Zwenger proposes the formula C20H18O8 >M. Neubauer prefers C^HjsOy. According to Dr. Strecker, catechuin is a

* “ Jahresb. fur Prakt. Pharm.,” xii., 162.

t Neubauer, “ Ann. der Chem. und Pharm.,” xcvi., 337.

$ The following are the most important papers on this subjedt, published in the periodicals—Nees von Esenbeck, “ Ann. der Chem. und Pharm.,” i., 343. Zwenger, “Ann. der Chem.und Pharm.” xxxvii.,320. Hagen, “ Ann. der Chem. und Pharm.,”xxxvii., 336. Delfts, loc.cit.Neubauer, Joe. lit. Van Delben and Kraut, “Ann. der Chem. und Pharm.,” cxxviii., 2S5.Schutzenberger and Rack, “ Bullet. Soc. Chimiq. de Paris,” July, 1865, p. 5.