164 



resin is red-yellow, fuses at 50°, dissolves in alcohol, ethei', and 

 alkalies, and has the formula C40 H25 O14. 



Orcill— Ci4 Hg O4 +2 HO. Peculiar, sweet substance; occurs in 

 Lecanora, Roccella, and Variolaria, lichens used for the preparatio 

 of archil and litmus. To obtain it, draw out with alcohol, evapo- 

 rate the solution, keep cold, pour off from the resin which will 

 have formed, evaporate the liquid to honey-consistence, draw oi^t 

 with water, evaporate the aqueous solution to the consistence of 

 syrup, keep cold, and purify the crystals which will have formed, 

 by recrystallising. — Forms colourless crystals, which become 

 anhydrous when diied in a vacuum and reciystallised in anhy- 

 drous ether ; of a very sweet but disagreeable taste, of neutral 

 reaction ; fuses with a gentle heat, losing its water; boils at about 

 280°, and distils undecomposed ; dissolves most readily in water, 

 alcohol and in ether. The aqueous solution yields, with chloride 

 of iron, a dark-red precipitate, from which the Orcin is dissolved 

 by ammonia ; sub-acetate of lead gives a white precipitate, turning 

 quickly red at the air. The solution, mixed with a little ammonia, 

 liecomes slowly brown-red when exposed to the air, under forma- 

 tion of Orcein =:Ci4 H7 NOß. Nitrate of silver, chloride of 

 mercury and sulphate of coppei' produce no precipitates with 

 Orcin. When mixed with nitrate of silver, and afterwards with 

 ammonia, a flocky precipitate is formed; on boiling the silver is 

 deposited as a mirror, and the liquid turns red. 



Oreoseloii. See Peucedanin. 



Otol)a-fat, from Myristica Otoba, is similar to nutmeg-balsam. 



Oxalic Aci(l=C2 O3 -\- HO -1- 2 eq. water. It occurs as an 

 acid Oxalate of alkalies in the stalks and leaves of Oxalidete, 

 Polygonece, and Chenopodese, and is widely distributed as Oxa- 

 late of lime, especially in roots and woods. The Oxalate of lime, 

 being insoluble in water and in vegetable acids (acetic acid, tfec), 

 does not pass into the aqueous vegetable extract. Oxalic acid was 

 formerly produced from species of Oxalis and Rumex, these herbs 

 containing a large quantity of the acid ; but at present it is pro- 

 duced more economically by the action of nitric acid on sugar, or 

 by treating certain organic substances (sawdust, &c.) with caustic 

 alkalies at rather high temperatures. — The pure Oxalic acid 

 crystallises in colourless and inodorous klinorhombic piisms and 

 needles of a strongly acid taste ; it loses in a gentle heat its 

 water of crystallisation (2 eq.), and volatilizes in a stronger heat 

 (at 1.50°) mostly imdecomposed in white, pungent vapours; on 

 rapidly heating it fuses at 98°, and is completely decomposed at 

 155° into formic acid, water, oxyd of carbon, and carbonic acid. 

 It dissolves in 10 parts cold, and in equal parts boiling water ; in 

 2.V parts cold, and in 2 parts boiling alcohol; little in ether. 



