AECHIL 203 



aqua regia are duo to its containing a compound of chlorine, nitrogen, and oxygen, 

 and confirms the generally received view, that its action depends upon free chlorine. 

 From the vapour evolved in the action of nitric upon hydrochloric acid, a liquid 

 may be condensed which is nearly of the composition N0 2 C1 3 (WOC1 2 ), containing, 

 however, no free chlorine : this compound, in the gaseous form, is known as chloro- 

 nitric gas. 



The best proportions for forming aqua regia appear to be about one volume of 

 strong nitric to three of hydrochloric acid. Aqua regia is used for dissolving both 

 gold and platinum. 



AQUA VITJ3G. The name given to alcohol when used as an intoxicating beve- 

 rage. It is derived from the alchemists, who, having obtained in all probability 

 from the Arabian physicians, since Avicenna uses the term the product by distilla- 

 tion of saccharine fermentation, al-kohol (alcohol), gave, upon the same principle as 

 guided them in calling the nitro-muriatic acid aqua regia, the name of aqua vites to 

 several ardent spirits ; and it has been retained especially with reference to whisky 

 and brandy. 



ARABIC, GUM. Gum Arabic exudes from several species of Acacia, as A. vera. 

 It is also found in the roots of the mallow, comfrey, and some other plants. Gum 

 Arabic never crystallises, is transparent, and has a vitreous fracture. 



ARABX1U 1 . The principal constituent of Gum Arabic. If gum is treated with 

 hydrochloric acid and alcohol, the lime, magnesia, and potash, in combination, are 

 decomposed, and the arabin is separated as a gum, exhibiting the properties of an 

 acid. In the moist state it dissolves in cold water, forming mucilage, from which it 

 is precipitated by alcohol. After drying, it no longer dissolves, but swells into a 

 gelatinous mass. Dried at 212 F. it has the composition C 12 H 11 0" (C 12 H 22 O n ). 

 See ACACIA, CKRASINB, DEXTRINE, GUM. 



ARAGOI7XTE. So called from Aragon, in Spain, where it was first discovered. 

 A carbonate of lime, crystallised in rhombic prisms, or in forms derived from the 

 same. Sometimes written ARRAGONITE. See LIME. 



ARBOR VXTJE. Several species of Thuja, found in America and China, are 

 called arbor vit<s. It is a light, soft, and fine-grained wood, which is used in several 

 kinds of carpentry. 



ARCH. As this dictionary is not intended to include articles connected with 

 engineering or with architecture, it would be out of place to describe the conditions 

 required to ensure the stability of the arch, which is manifestly one of great impor- 

 tance to the practical builder. (For the theory of the equilibrium of the arch, Gwilt's 

 treatise on the subject should be consulted, or the article Arch, 'Encyclopaedia 

 Britannica.') It simply remains to define the arch as a structure of stone or brick, 

 supported by its own curve ; or of wood or iron, supported by the mechanical arrange- 

 ments of the work. 



The curvature of an arch may vary very considerably. Where the arch is low, the 

 circle it belongs to becomes very large ; and the strength of arches varies greatly with 

 their forms ; they may be either segments of a circle, a parabola, an ellipse, an 

 hyperbola, or a catenary. 



The arch in architecture is the means of passing from one pillar to another ; and 

 we have the circular form, which was succeeded by the pointed arch, and all its 

 modified forms of foliation, &c. 



ARCHERY BOW. These are divided into the ' single-piece bow ' and the ' back 

 or union bow! 



The single-piece bow is made of one rod of hickory, lance-wood, or yew-tree, which 

 last, if perfectly free from knots, is considered the most suitable wood. 



The union bow is made of two or sometimes three pieces glued together. The 

 back ' piece, or that furthest from the string, is of rectangular section, and always of 

 lance-wood or hickory ; the ' belly,' which is nearly of semicircular section, is made of 

 any hard wood that can be obtained straight and clean, as ruby-wood, rose-wood, 

 green-heart, king-wood, snake-wood, &c. Sometimes the union bow is imitated by 

 one solid piece of straight cocoa-wood of the West Indies (not that of the cocoa-nut 

 palm), in which case the tough fibrous sap is used for the back. The Palmyrea is 

 also used for bows. HoltzapffeL 



ARCHZXi. (OrseUle, Fr. ; Orseille, Ger. ; OriceUo, Ital.) The name of archil is 

 given to a colouring-matter obtained, by the simultaneous action of the air, moisture, 

 and an ammoniacal liquor, from many of the lichens, the most esteemed being the 

 Boccetta. 



It appears in commerce in three forms : 1, as a pasty matter called archil; 2, as a 

 mass of a drier character, named persis ; and 3, as a reddish powder called cudhcar. 



The lichen from which archil is prepared is known also as the canary weed or 

 orchilla weed, It grows in great abundance on some of the islands near the African 



