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LEFT CRYPT 211 CRYSTAL been worked since 1857, and are appar- ently inexhaustible. None of the finest specimens, however, reach the United States, as the mines are owned by the Danish government and the best of their product is taken to Copenhagen. Among the resulting products are soap, baking soda, washing soda, aluminum sulphate, and a kind of glass which resembles porcelain. CRYPT, originally a subterranean cell or cave, especially one constructed for sepulture. From the usage of these by the early Christians crypt came to signify a church underground or the lower story of a cathedral or church. It is usually set apart for monumental pur- poses, and is sometimes used as a chapel. The crypt is a common feature of cathe- drals, being always at the east end, under the chancel or apse. The largest in England is that of Canterbury Cathe- dral. CRYPTOGRAPHY, the art of writing in secret characters or cipher, or with sympathetic ink. The simplest method consists in choosing for every letter of the alphabet some sign, or another letter or group of letters. Even the more complex, however, present, as a rule, only temporary difficulty to an expert. The fact that the most frequently recur- ring letter in the English language is the letter e, that the most common double vowels are ea and ou, that r, 8, and t are the most frequent terminal letters, etc., are of no small assistance in forming a key to any given cryptogram. See Cipher Writing. CRYPTOPROCTA, a fierce carnivorous animal of Madagascar, forming a genus and species by itself. It is plantigrade^ but resembles a weasel, three feet long, and attacks the largest animals with great ferocity. CRYSTAL (ice), in chemistry and mineralogy, a clear transparent body, which, by the mutual attracti'^n of its particles, has assumed the form of some one of the regular geometric solids, being bounded by a certain number of plane surfaces. A crystal consists of three parts. First, plane surfaces, called faces, which are said to be similar when they are equal to each other and are similarly situated; dissimilar, when they are unequal or have a different position. Second, edges, formed by the meeting of two faces. They are said to be similar ■when formed by similar faces; dissimi- lar, by dissimilar faces. Equal edges are formed when the faces are inclined at the same angle to one another; un- equal, when they are inclined at different angles. Third, solid angles, formed by the meeting of three or more faces; and in this case also they are similar and dis- similar, equal and unequal angled edges. The chemist procures crystals either by fusing the bodies by heat and then allow- ing them gradually to cool, or by dis- solving them in a fluid and then ab- stracting the fluid by slow evaporation. The method of describing and classifying crystals (now universally adopted) is based upon certain imaginary lines drawn through the crystal, and called its axes. There are seven of these systems, six of which refer to three axes and one to four, and they are subdivided accord- ing as the axes are at right angles (orchometric) or not (chinometric). When the axes are equal and at right angles the system is called isometric. When the angles are right angles, but only two are equal, the system is called tetragonal. When the three axes are at right angles but all unequal, the system is called orthorhombic. The classes are as follows: First, the monometric, regu- lar, or cubic system, in which the axes are equal and at right angles to one another; second, the square prismatic or dimetric system, in which the axes are at right angles to each other, and while two are equal, the third is longer or shorter; third, the right prismatic, rhombic, or trimetric system, in which the axes are at right angles to each other, but all are of different lengths; fourth, the hexagonal or rhombohedral system, which has four axes, three in one plane inclined to each other at 60 degrees, the fourth perpendicular to this plane; fifth, the monoclinic or oblique system, in which two axes are at right ar.j-les and the third is inclined to their plane; sixth, the diclinic or doubly oblique system, in which two axes are at right angles, the third oblique to both; seventh, the triclinic system, in which the three axes are inclined to each other at any an^'ie other than a right angle. The power of forming crystals is pos- sessed by a great majority of inorganic combinations whether natural or artifi- cial, and also by a large number of organic chemical bodies. The decree of this capacity varies greatly in different substances, so that certain chemical com- binations are found only in crystals, others rarely. Bodies which entirely lack the power of forming crystals or crystalline aggregates are called amor- phic. The size of crystals also varies greatly. Some are very large, others are only aggregations of microscopic crys- tals. The infinitesimally small crystals are called microliths. Crystals grow by the deposit of new horizontal layers