309 



CRAMP. 



CRAYONS. 



310 



employed, whether that expansion arise from heat, or from the mere 

 crystallisation of the mortars, cements, or plasters. (See Eck. ' Traite 1 

 de Construction en Poteries et Fer,' Paris, 1841 ; ' Papers of Royal 

 Inst. of Brit. Architects,' January, 1854. 



CRAMP. [SPASM.] 



CRAMP. A small piece of metal used for tying together the build- 

 ing materials of large dimensions which cannot be bound by the mere 

 adhesion of the cementitious substances with which they are bedded. 

 Cramps are made of iron, of copper, or of gun metal, and they are run 

 with lead or with sulphur, or cement, according to the position they 

 are used in ; their form is either that of a flat piece of metal with the 

 two ends turned downwards, thus r " 1 or it may be simply a flat piece 

 of metal made to present a double wedge on plan thus >- . As iron 

 is liable to absorb moisture, even in the interior of a stone, and then to 

 pass into the state of the hydrous oxide, a process always accompanied 

 by an increase of volume, it is advisable only to use iron cramps 

 when the stones they are intended to connect have a considerable 

 thickness ; and for thin ashlar work copper or gun-metal cramps 

 should alone be used. In marble works copper cramps are preferable, 

 but they must be run with plaster, or sulphur. 



CRANE. A machine used in building, and in ordinary commercial 

 operations for the purpose of hoisting weights. It may be described 

 as consisting of an upright post, bearing a projecting arm or jib, usually 

 stiffened by a bracket ; and a barrel, winch, pinion, and handles, to 

 receive a fall passed over a sheaf at the head of the jib, and reeved 

 into the block which bears the hook on which the load is ultimately 

 brought. The upright post is, generally speaking, made so as to be 

 able to revolve on its centre, and thus an article raised at any one 

 point may be deposited at any other point within the sweep of the jib. 

 Cranes are made either fixed or movable, single or double ; as pit 

 cranea, or those which have their foundations below the ground ; or as 

 derricks, or those which have their framework and stays above the 

 surface. 



Cranes differ from crabs in this respect, namely, that in consequence 

 of their possessing jibs, the former are able to deposit their load where 

 it may be desired; whereas crabs can only deposit their load vertically, 

 under the last block connected with them. 



I; AXIOLOGY. [PHRENOLOGY.] 



CRANK. A portion of machinery used, together with a connecting 

 rod, for the purpose of converting rectilineal into circular motion, or 

 rice vend. Thus, in an ordinary steam-engine the upward and down- 

 ward motion of the piston is made to give a circular motion to the 

 crank, by the interposition of the connecting rod, which bears joints at 



[Front tiew.] 



[Side rievr.] 



its respective ends ; and then the upward motion of the piston causes 

 the crank to pass over half of its circle of revolution, whilst, the down- 

 ward motion carries it over the remainder of its path. Evidently in 

 such an arrangement there must be two points, that is to say, when the 

 piston is respectively at the top and bottom of iU stroke, wherein it 

 exercises no power over the crank ; and when the crank is upon the 

 horizontal line passing through its own axis the power exercised upon 

 it is the greatest. It is for the purpose of carrying the crank over 

 these dead, or weak points that the fly-wheel is introduced into the 



. notion of engines, and numerous other contrivances have been 

 suggested with a view to reduce or annihilate the irregularity of the 



i . without, however, producing any practical improvement ; so that 

 at the present day the constructors of machinery continue to use the 

 crank and connecting rod in the majority of cases wherein they desire 

 to convert jwr-pendicular into circular motion. In the treatise on the 

 Sti-iiin Rngine, by Mr. J. Scott Russell, Edin. 1841, the question of the 

 Hu|.pi>Hc-(l li of power by the use of the crank is very ably discussed. 

 See also Hann and Oenur, ' The Steam Engine,' 8vo, London, 1854 ; 



Moseley's 'Mechanical Principles of Engineering and Architecture,' 

 Svo, Lond. 1843. 



CRAPE is a light transparent fabric composed of silk, from which, 

 by the mode of its preparation, all the gloss has been taken. When 

 dyed, as it usually is, of a black colour, it is worn as a material for 

 mourning dresses. 



The weaving of crape is conducted at a hand-loom, according to the 

 simplest method of the weaver's art : all its peculiarity being given to 

 it in the dressing, which it receives after it is taken from the loom. 

 The silk is used without having been washed or dyed, and consequently 

 with all the natural viscid gum which forms a part of its composition 

 as spun by the worm. For thin crape, the only preparation which the 

 filaments undergo previous to the weaving is the simple twisting, 

 which forms the first process of the throwing mill, and in which state 

 the thread is technically called singles. When it is intended to make a 

 more substantial fabric, the warp is formed of two and sometimes three 

 filaments twisted together, which in that state are called tram : the 

 weft is still composed of singles. After the web is taken from the 

 loom, it is dressed with a viscid solution of gum, which in drying 

 causes the individual threads to resume, as far as the interlacing will 

 admit, the form they originally held previous to then- being twisted in 

 the throwing mill ; it is by this means that is produced the peculiar 

 wrinkled appearance by which crape is distinguished. This fact will 

 be shown if a piece of crape is washed in water hot enough to discharge 

 the gum, when the web will resemble thin gauze. 



CRAYONS (from the French crayon, derived from crate, chalk) are 

 a species of material for drawing. They may be classed in two kinds, 

 native and artificial. The principal native crayons are black, white, 

 and red. The best black is procured from Italy. It is a species 

 of earth, which is soft in the ground, but hardens on exposure to the 

 air. It is of a bright even tint, and of a smooth and moderately hard 

 texture. Admirably adapted to outlining and shading drawings of any 

 size, it is to the artist an excellent tool for study. It will form a large, 

 bold, and strong line, and is at the same time capable of great fineness. 

 The best white is a pure chalk, and is procured in France. It is of a 

 brilliant colour, but very brittle; so that it is difficult to avoid 

 breaking it frequently. There are various modes of correcting its 

 brittleness, such as soaking it in milk, baking it on hot iron, or in the 

 fire; but they all, more or less, injure the brilliancy of its tint. Pipe- 

 clay is sometimes employed as a substitute, as being smoother and less 

 brittle ; but it is of a very inferior tint. White chalk is used on tinted 

 paper to touch on or hatch the high lights. It is also much used by 

 the painter to determine or correct his outline. Red chalk is employed 

 in the place of black chalk on white or tinted paper, because it is freer 

 than the best black chalk, and firmer and smoother than the inferior 

 kinds. It is also of a warmer and more agreeable tone of colour ; but 

 it is by no means capable of the same degree of fineness in small or 

 highly finished drawings; it is a clayey ochreous substance. All these 

 three kinds of native crayons are frequently combined in the same 

 drawing, on tinted papers, which are generally of a neutral gray, of a 

 bluish, greenish, or brownish quality. 



The native crayons are the legitimate materials for the artist in the 

 study of drawing, and in tracing the first thoughts of design. Some 

 of the sketches of Raffaele, Michel Angelo, the Caracci, and others of 

 the great painters, remain to attest the utility of crayons in forming 

 the style of a painter or sculptor, and their capability of expressing 

 the highest qualities of design. 



Artificial crayons are composed of different coloured earths, and 

 other pigments, rolled into solid sticks with some tenacious stuff sueh 

 as milk, common gin, or beer-wort. The beat are procured from 

 Switzerland ; but very excellent academy crayons are made in this 

 country, and in Germany. Those made in Germany are most suited 

 to large works, such as studies for fresco paintings, &c. Artificial 

 crayons are employed in crayon painting upon a ground composed of 

 paper or vellum, stretched upon a canvas, which has been previously 

 extended on a deal frame. It is requisite to paint with cooler tints in 

 crayons than in oils, which is the reason why crayon painters generally 

 fall into such a cold style of colouring when they work in the other 

 material. Great softness and delicacy and great vivacity of tint may 

 be obtained in finished crayon paintings ; but depth, richness, and truth 

 of colour, are not obtainable, nor solidity in the forms. Moreover, the 

 delicacy proper to the substance is tolerably certain to betray the 

 artist who devotes himself solely to its use into a petty and weak 

 style of drawing. For sketches of portraits, in which the form and 

 expression, and a general idea of the complexion, are all tliat is 

 required, crayons are a pleasing and useful material ; but they should 

 be employed only occasionally, and as a variety to other modes of 

 study. 



Considered as a branch of manufacture, crayons, as we have stated 

 above, have been more carefully attended to by the French than the 

 English. There are many recipes for the preparation of them : sper- 

 maceti, bone-ash, and boiling water ; pipeclay, prepared chalk, colouring 

 matter, and pale mild ale ; white soap, rectified spirits of wine, washed 

 clay, chalk, colouring matter, and boiling water ; pure clay, shellac, 

 spirits of wine, oil of turpentine, and colouring matter ; fine pale blue 

 clay, shellac, wood naphtha, and colouring matter : all are recipes in 

 practical use. The colouring matter differs greatly in kind ; mere 

 difference of tint is produced by diluting with washed chalk; but 



