MUCILAGE 371 



wrinkles or furrows which run across the surface of every slice act upon the reflected 

 light in such a way as to produce the chromatic effect ; for Sir David Brewster has 

 shown that if we take with very fine black wax, or with the fusible alloy of D'Arcet, 

 an impression of mother-of-pearl, it will possess the iridescent appearance. Mother- 

 of-pearl is very delicate to work, but it may be fashioned by saws, files, and drills, 

 with the aid sometimes of a corrosive acid, such as the dilute sulphuric or muriatic ; 

 und it is polished by colcothar of vitriol. 



MOTHER-WATER is the name of the liquid which remains after all the salts 

 that will regularly crystallise have been extracted, by evaporation and cooling, from 

 any saline solution. 



MOUXiDS, ELASTIC. Being much engaged in taking casts -from anatomical 

 preparations, Mr. Douglas Fox, surgeon, Derby, found great difficulty, principally 

 with hard bodies, which, when undercut, or having considerable overlaps, did not 

 admit of the removal of moulds of the ordinary kind, except with injury. These diffi- 

 culties suggested to him the use of elastic moulds, which, giving way as they were 

 withdrawn from complicated pai-ts would return to their proper shape ; and he ulti- 

 mately succeeded in making such moulds of glue, which not only relieved him from 

 all his difficulties, but were attended with great advantages, in consequence of the 

 small number of pieces into which it was necessary to divide the mould. 



The body to be moulded, previously oiled, must be secured one inch above the 

 surface of a board, and then surrounded by a wall of clay, about an inch distant from 

 its sides. The clay must also extend rather higher than the contained body : into 

 this warm melted glue, as thick as possible so that it will run, is to be poured so as to 

 completely cover the body to be moulded : the glue is to remain till cold, when it will 

 have set into an elastic mass, just such as is required. 



Having removed the clay, the glue is to be cut into as many pieces as may be 

 necessary for its removal, either by a sharp-pointed knife, or by having placed threads 

 in the requisite situations of the body to be moulded, which may be drawn away 

 when the glue is set, so as to cut it out in any direction. 



The portions of the glue-mould having been removed from the original, are to be 

 placed together and bound round by tape. 



In some instances it is well to run small wooden pegs through the portions of glue, 

 so as to keep them exactly in their proper positions. If the mould bo of considerable 

 size, it is better to let it be bound with moderate tightness upon a board to prevent 

 it bending whilst in use; having done as above described, the plaster-of-Paris, as 

 in common casting, is to be poured into the mould, and left to set. 



In many instances wax may also be cast in glue, if it is not poured in whilst too 

 hot ; as the wax cools so rapidly when applied to the cold glue, that the sharpness 

 of the impression is not injured. 



Glue has been described as succeeding well where the elastic mould is alone ap- 

 plicable; but many modifications are admissible. When the moulds are not used 

 soon after being made, treacle should be previously mixed with the glue (as employed 

 by printers), to prevent it becoming hard. 



The description thus given is with reference to moulding those bodies which cannot 

 be so done by any other than an elastic mould ; but glue moulds will be found greatly 

 to facilitate casting in many departments, as a mould may be frequently taken by this 

 method in two or three pieces, which would, on any other principle, require many. 



MOUNTAIN 1 BXiTTE. Blue copper ore. See COPPEH. 



MOUNTAIN 1 CORK. A form of asbestus. See ASBESTUS. 



MOUNTAIN GREEN. Malachite, or green carbonate of copper. See COPPER. 



MOUNTAIN XiEATKER. Asbestus is so called when it is so interlaced that the 

 fibrous structure is not apparent. See ASBESTUS. 



MOUNTAIN XilMESTONE. A term commonly applied to the carboniferous 

 limestone, on account of its masses forming some of our finest mountain scenery. It 

 may be regarded as the boundary rock of nearly all our coal-formations. See CARBO- 

 NIFEROUS LIMESTONE. 



MOUNTAIN SOAP (Savon de montagne, Fr. ; Bergscife, Gor.) is a tender 

 mineral, soft to the touch, which assumes a greasy lustre when rubbed, and falls to 

 pieces in water. It consists of silica 44, alumina 26'5, water 20*5, oxide of iron 

 8, lime 0'5. It occurs in beds, alternating with different sorts of clay, in the Isle of 

 Skye, at Billin in Bohemia, &c. It has been often, but improperly, confounded with 

 steatite. 



MUCIC ACID (Acid muciqiie, Fr. ; ScMeimsdure, Ger.) is the same as the sac- 

 lactic acid of Scheele, and may be obtained by digesting one part of gum arabic, 

 sugar-of-milk, or pec.tic acid, -with twice or thrice their weight of nitric acid. It forms 

 white granular crystals, and has not been applied to any use in the arts. 



JMCUCIfiAGE is a solution in water of gummy matter of any kind. 



