ANTHRACITE 191 



form resembles that of a pear, rounded at ono extremity, and tapering to a very 

 slender tail at the other. If a part of tho tail be broken off, the whole drop flies to 

 pieces with a loud explosion ; and yet the tail of a drop may be cut away by a glass- 

 cutter's wheel, or the thick end may bo struck smartly with a hammer, without the fear 

 of sustaining any injury. When heated to redness, and permitted to cool gradually in 

 the open air, they lose these peculiarities, and do not differ sensibly from common glass. 



Tho peculiar brittleness of unannealed glass is, by many manufacturers, referred to 

 the following conditions. The exterior surface of the glass cooling quicker than the 

 layers of glass beneath, the two portions of glass are supposed to be in different 

 degrees of tension ; as they technically express it, a stretched skin of glass is formed ; 

 and as the arrangement of the particles is different in this film from their disposition 

 in those parts which have cooled more slowly, there is a constant tendency to fracture, 

 the slightest scratch upon this ' skin ' disturbing the entire molecular arrangement. 



If any mass of glass or of metal cools rapidly, there will be, according to the 

 thickness of the mass, a greater or less difference between the arrangement of the 

 constituent particles on the outer and inner sections. The process of annealing 

 secures an equal arrangement throughout the mass. 



"When metals have been extended to a certain degree under the hammer, they 

 become brittle, and incapable of being further extended without cracking. In this 

 case the workman restores their malleability, sometimes by annealing, or, in other 

 cases, by heating them red-hot and allowing them to cool slowly. The rationale of 

 this process seems to be, that the hammering and extension of the metal destroys 

 the kind of arrangement which tho particles of the metal had previous to the ham- 

 mering; and that the annealing, by softening the metal, enables it to recover its 

 original structure. 



Of late years a mode has been discovered of rendering cast-iron malleable, without 

 subjecting^ it to the action of puddling. The process is somewhat similar to that 

 employed in annealing glass. The metal is kept imbedded in ground charcoal, or in 

 powdered haematite, for several hours at a high temperature, and then allowed to cool 

 slowly. In this manner vessels are made of cast-iron which can sustain considerable 

 violence without being broken. See IKON, MALLEABLE. 



ANNOTTO or ANATTO. See ARNATTO. 



ANORTHITE. A lime felspar. See FELSPAR. 



ANTELOPE HORN is used occasionally for ornamental knife-handles. See 

 HORN. 



ANTHRACENE. C 28 H 10 (C 14 H">). A hydrocarbon, known also as paranaphtha- 

 line, discovered by J. Dumas in 1831. It has become of considerable commercial 

 importance since Messrs. Graebe and Liebermann discovered, in 1869, that anthracene 

 could be converted into a valuable colouring-matter identical with the natural alizarine 

 of the madder-root. 



Anthracene is produced in the dry distillation of coal, bituminous shale, or wood ; 

 and is found in the heavy semi-fluid portion of the tar which comes over towards the 

 close of the distillation. The substance known as 'green grease,' obtained by dis- 

 tilling coal-tar, and used as a common lubricating agent for machinery, contains about 

 20 per cent, of anthracene associated with naphthaline and other hydrocarbons. From 

 this product, crude anthracene may bo obtained by the use of tho hydro-extractor, 

 and by submitting the raw product to strong pressure. The crude anthracene is 

 purified by solution in hot coal-tar naphtha and repeated recrystallisation. A yellow 

 tint, due to the presence of chrysogen, may be expelled by exposure to sunlight, and 

 the^ anthracene is finally purified from any other hydrocarbons by boiling with alco- 

 holic picric acid. 



Thus obtained, the pure anthracene appears in small, well-defined, lustrous crystalline 

 laminae of a clear white colour, and exhibiting, when pure, a beautiful violet fluo- 

 rescence^ The specific gravity of anthracene is 1-149. It melts at about 415 F., 

 and sublimes at higher temperatures. Anthracene is insoluble in water, but readily 

 soluble in boiling alcohol, in ether, benzole, volatile oils, and bisulphide of carbon. 

 By prolonged exposure to light it passes into an isomeric modification known as 

 paranthracene. Under the influence of oxidising agents it is converted into anthra- 

 quinone, from which artificial alizarine may be prepared. See ALIZABINE. 



ANTHRACENE-RED. A name for artificial alizarine. See ALIZARINE. 



ANTHRACITE. (&v6pa, coal.) A variety of coal containing a larger propor- 

 tion of carbon and less bituminous matter than common coal. De la Seche. 



'"We see the same series of coal-beds becoming so altered in their horizontal 

 range, that a set of beds bituminous in ono locality is observed gradually to change 

 into anthracitic in another. Taking the coal-measuros of South Wales and Monmouth- 

 shire, wo have a series of accumulations in which the coal-beds become not only more 

 anthracitic towards the west, but also exhibit this change in a piano which may 



