ORPIMENT 461 



Any convenient quantity of the orchella weed may be cut into very small pieces, 

 and then macerated with milk of lime, till the colouring-matter is extracted. Three 

 or four macerations are quite sufficient for this purpose, if the lichen has been suffi- 

 ciently comminuted. The clear liquors should be filtered and mixed together. A 

 solution of bleaching-powder of known strength should then be poured into the lime 

 solution from a graduated alkalimeter. The moment the bleaching-liquor comes in 

 contact with the lime solution of the lichen, a blood-red colour is produced, which 

 disappears in a minute or two, and the liquid has only a deep yellow colour. A new 

 quantity of the bleaching-liquid should then be poured into the lime solution, and the 

 mixture carefully stirred. This operation should be repeated so long as the addition 

 of the hypochlorite of lime causes the production of the red colour, for this shows that 

 the lime solution still contains unoxidised colorific principle. Towards the end of the 

 process, the bleaching-solution should bo added by only a few drops at a time, the 

 mixture being carefully stirred between each addition. We have only to note how 

 many measures of the bleaching-liquid have been required to destroy the colouring- 

 matter in the solution, to determine the amount of the colorific principle it contained. 

 Dr. Stenhouse suggests the following method for extracting the colorific principle for 

 transport : Cut the lichens into small pieces, macerate them in wooden vats with 

 milk of lime, and saturate the solution with either muriatic or acetic acid. The gela- 

 tinous principle is then to be collected on cloths and dried by a gentle heat. In this 

 way the whole of the heat can be easily extracted, and the dried extract transported 

 from the most distant localities. See ARCHIL ; LICHENS. 



ORCHIL. See ARCHIL. 



ORCXXT is the name of the colouring-principle of several of the lichens. The 

 lichen dried and pulverised is to be exhausted by boiling alcohol. The solution 

 filtered hot lets fall, in the cooling, crystalline flocks, which do not belong to the 

 colouring-matter. The supernatant alcohol is to bo distilled off, the residuum is to 

 be evaporated to the consistence of an extract, and triturated with water till this 

 liquid will dissolve no more. The aqueous solution, reduced to the consistence of 

 syrup, and left to itself in a cool place, lets fall, at the end of a few days, long brown 

 brittle needles, which are to be freed by pressure from the mother-water, and dried. 

 That water being treated with animal charcoal, filtered and evaporated, will yield a 

 second crop of crystals. These are orcin. See LICHEN ; LITMUS. See also Watts's 

 ' Dictionary of Chemistry.' 



OH.DE.ai. BEAN. The Calabar bean ; the seeds of Physostigma venatum, Balf. 



ORE. The natural chemical compound of a metal with some other element, such 

 as oxygen, sulphur, arsenic, &c. These elements have been sometimes termed 

 mincralisers ; and when metals are found free from them they are called native metals, 

 and not ores. 



OREXDE is the name given by MSI. Meurier and Valient, of Paris, to an alloy 

 which has a golden brilliancy. It is composed of copper 100, zinc 17, magnesia 6, 

 sal-ammoniac 3'6, quicklime 1'80, and tartar of commerce 9. 



The copper is first melted, and then the other things are added by small portions at 

 a time, skimming, and keeping in fusion for about half an hour. 



The oreide, which is a brass, has a fine grain, is malleable, takes a most brilliant 

 polish, and, if it tarnishes, its lustre is restored by acidulated water. 



OREXiIiIN*. A yellow colouring-matter contained in arnatto. It is soluble in 

 water, in alcohol, and ether. It dyes alumed goods yellow. 



ORES, DRESSING OF. See DRESSING OF ORES. 



ORICHAXiCUXK. An old alloy, called also false silver. 



ORIENTAL EMERAXiX). The name given to green sapphire. 



ORXEXTTAXi TOPAZ. The name given to yellow sapphire. 



OR-IMCOIiV. A brass, in which there is less zinc and more copper than in the 

 ordinary brass ; the object being to obtain a nearer imitation of gold than ordinary 

 brass affords. In many of its applications the colour is heightened by means of a 

 gold lacquer, but in some cases, and, as we think, with very great advantage, the true 

 colour ot the alloy is preserved after it has been properly developed by means of dilute 

 eulphuric acid. 



ORPIMEirT (Eng. and Fr. ; Operment, Eauschgelb, Ger. ; Yellow sulphide of ar- 

 senic) is found native in many parts of the world, as in Hungary, Turkey, China, &c. ; 

 the finest specimens being brought from Persia, in brilliant yellow masses, of a lamellar 

 texture, called ' golden orpiment.' 



Native orpiment is the auripigmentum, or paint of gold, of the ancients. It was so 

 called in allusion to its use and its colour, and also because it was supposed to con- 

 tain gold. From this term the common name of ' orpiment,' or ' gold paint,' has been 

 derived. 



In nature it is found most generally in amorphous masses of a bright yellow colour, 



