285 



LIGHTS AT SEA. 



LIME. 



also produces nearly three pounds of carbonic acid, and a pound of gas 

 two and a half pounds of carbonic acid. For every cubic foot of gas 

 burned, rather more than a cubic foot of carbonic acid is produced." 

 As the water produced deadens the effect of the flame, and as the 

 carbonic acid is very deleterious to the lungs, Dr. Faraday contrived a 

 mode of carrying both off without allowing them to mix with the air 

 of the room. Air is admitted to feed the flame, nearly in the usual 

 way ; but when the products of combustion have arrived at the top of 

 the glass chimney, their progress is arrested by a covering of talc, and 

 they are compelled to pass down between the chimney and another 

 larger glass chimney concentric with it. The open space between* the 

 two chimneys communicates with a pipe which is conducted in any 

 convenient way into the open air; the carbonic acid, aqueous vapour, 

 smoke, and other emanations from the Same have no means of escape 

 except through this tube, and they are thus wholly cut off from con- 

 tact with the air of the room. The mode of carrying out the 

 arrangement may be varied in its details ; but the general result is said 

 to be that the light is brighter, the space around the lamp cooler, and 

 the air of the room less vitiated than when common open burners are 

 mad. 



Many other ingenious arrangements have since been adopted by 

 different inventors ; either to lessen the production of smoke, or to 

 carry off the products of combustion without allowing them to mix 

 with the air of the room. 



LIGHTS AT SEA. So much attention has been already given to 

 this subject under the heading COLLISIONS AT SEA in this work, that 

 little remains to be noticed here. The suggestions therein made have 

 been well received by officers of the navy and merchant services, and 

 the question is by no means dormant with the authorities; a perfect 

 system of lighting our coaBte seems to be not distant. 

 LIGHTS, FLOATING. [TRINITY HOUSE.] 

 LIGHTS, NORTHERN. [POLAR LIGHTS.] 



LIGNIN. From the Latin lignum, wood. The structure of wood 

 is determined by the superposition of a number of little cells or vessels, 

 more varied in shape but somewhat resembling those of the honeycomb. 

 The material composing this structure is cellulose [CELLS ; TISSUES, 

 VEGETABLE, in NAT. HIST. Div.], but the chief substance which fills 

 up the cell, which incrusts and even penetrates the walls, and which 

 gives firmness and hardness to the whole, is liynin. The harder and 

 tougher a piece of wood, the more lignin does it contain. 



The purification of lignin, so as to obtain it in a state sufficiently 

 free from other matter to admit of a determination of its composition 

 being made, is exceedingly difficult. Like cellulose it is insoluble in 

 water, alcohol, ether, or dilute acids, and may therefore be freed from 

 many other matters by successively treating it with these agents. Its 

 chief characteristic is, however, a greater solubility in alkaline liquids 

 than is possessed by cellulose. 



Lignin contains a greater per centage of hydrogen than is necessary 

 to form water with its oxygen, whereas cellulose contains these two 

 elements in exactly the required proportions, cellulose being represented 

 by the formula C., 4 H. 0., , whilst ligniu has been described as C 3= H., 4 O., . 

 Submitted to destructive distillation liguin yields acetic acid, hence the 

 source of that acid, when wood is strongly heated in iron cylinders, as 

 described in treating of pyruHgneont acitl [ACETIC ACID]. That it is 

 the lignin which chiefly furnishes the acid is proved by the fact that 

 the hardest varieties of wood those containing most incrusting matter, 

 or lignin yield the largest amount of acid, when equal weights of the 

 wood are operated upon. 



Lignin is slowly acted upon by chlorine, and is dissolved by an 

 aqueous solution of that gas. Sulphuric acid abstracts water from it, 

 and sets free carbon. Iodine does not colour it. It is tasteless and 

 odourless, and in insoluble in water and alcohol. 



Lignin is identical with the substance noticed by Payen as Jfaliire 

 incritfitante. 



In its isolated condition lignin has no practical value, but the appli- 

 cation of it as ligneoui fibre in the manufacture of linen, cotton, hemp, 

 Ac., Ac., is obviously of the highest importance. 

 See also LIGNIN, in NAT. HIST. Div. 



LIGNOHB, a volatile liquid obtained from crude wood spirit. It is 

 probably a mixture of several substances, as analyses of this body made 

 !<y diiterrnt chemists exhibit great discrepancies. 



LIGU8TRIN, a bitter solid substance, of unknown composition, 

 found in the Liguttrnm rulgare. 



LILAC1N a crystalline substance found in the buds and 



bark of the common lilac. It possesses a nauseous bitter-sweet taste, 

 is soluble in 8 to 10 parts of water, or the same amount of alcohol, but 

 insoluble in ether. Dissolved in concentrated sulphuric acid, the 

 solution first assumes a greenish-yellow tint, passing gradually to a 

 vi6*let-blue, which becomes amethyst-red when diluted with water, 

 l.ilacin does not contain nitrogen, but its exact coinpositi'm is 

 unknown. 



1. 1 MB. (Astronomy.) The edge of a planet is called its limb ; also 

 the edge of any circle which forms part of an astronomical instrument. 

 LIME. In building operations limt, the dehydrised oxide of calcium, 

 in its various modifications is used for the purpose of forming the 

 material by means of which the small materials used in masonry or 

 brickwork, are bound or cemented together; and the precise word 

 lime is uaed in contradistinction to platter (or the sulphates of lime), 



or of cement (or the highly silicated carbonates of lime and alumina), 

 to designate the materials obtained from the calcination of carbonates 

 of lime of comparatively pure and simple composition. The various 

 descriptions of limes, technically considered, are those which are known 

 by the names of the rich, the poor, the moderately hydraulic, the 

 hydraulic, and the eminently hydraulic limes ; and the application of 

 these names depends exclusively upon the manner in which the re- 

 spective limes pass through the stages ofj slaking, or of setting. Very 

 little attention is paid in practical building operations to the mechan- 

 ical structure of the stones from which the various limes are obtained, 

 and the qualities of the caustic limes themselves constitute the only 

 recognised elements of the classification. 



The materials obtained from the calcination of limestones contain- 

 ing less than 6 per cent, of the silicate of lime, and otherwise composed 

 of the pure carbonate, are those called the rich limet, on account of the 

 remarkable increase of volume they assume when water is added to them 

 (or when they are ilakcd), for the purpose of being reduced to the state 

 of the plastic material, to be subsequently mixed with sand, for the for- 

 mation of mortar. They increase, in fact, as mxich as 3 4 or 4 J of their 

 original volume when measured in the lump, and about | of their 

 original weight ; they absorb in so doing about 1 4 times their bulk of 

 water. Naturally contractors prefer limes of this description ; for, to use 

 one of their own phrases, " they carry more sand ;" but such pure rich 

 limes never set (or harden by crystallisation), when in large bodies, or 

 large masses of work, and they are very soluble in frequently renewed 

 water. It follows, therefore, that pure rich limes should never be 

 used for external walling, or for works likely to be exposed to the 

 action of running or of tidal water. In sea water another source 

 of danger arises from the tendency of the lime to pass into the state of 

 the sulphate of that base. Some curious illustrations of the length of 

 time during which large bodies of slaked rich lime will remain in a 

 plastic state are to be found recorded in Vicat's ' Recherches sur les 

 Chaux." 



When the limestones operated upon contain from 1 to 30 per cent, 

 of impurities, such as the oxides of iron, manganese, magnesia, and 

 sand in the form of insoluble silica, they yield limes which do not 

 increase in bulk when slaked (in any notable manner) ; and are there- 

 fore known as the poor limes. The hydraulic limes, to be noticed 

 hereafter, are also poor, in so far as their expansion is concerned ; but 

 they differ from the class usually known by that name in this respect, 

 namely, that the poor limes, containing impurities such as are 

 above-named, do not set under water within any reasonable time, if 

 at all ; whereas, the hydraulic limes possess that faculty in variable 

 degrees. 



The hydraulic limes are those which are obtained from the calcina- 

 tion of limestones containing proportions of the silicate of alumina, in 

 combination with the pure oxide of calcium, varying within the limits 

 of from 6 to 30 per cent, of the silicate of alumina in the whole mass ; 

 and it appears that it is upon the greater or less rapidity of formation, 

 and of the stability of the hydrated silicate of lime and alumina 

 thus formed by the addition of water to the caustic lime, that this 

 class of materials owes the power of setting under water, and of 

 resisting the solvent action of the latter, from which circumstance its 

 name is derived. When the proportion of the silicate of alumina 

 ranges between the limits of from 6 to 8 or 12 per cent., the lime 

 becomes simply moderately hydraulic ; when the proportion ranges 

 between 12 and 20 per cent., the lime is hydraulic; and when it 

 ranges between 20 and 30 per cent., the lime becomes cmim-nt/// 

 hydraulic ; and at last closely approaches the character of the cements. 

 According also to the proportion of the silicate of alumina present in 

 the limestone is the lime obtained from it more or less rich, for the 

 moderately hydraulic limes swell nearly as much as the rich limes in 

 slaking, and with nearly equal rapidity and evolution of heat ; whereas 

 the hydraulic limes only increase from If to 24 of their original 

 volume, they slake slowly, and give out comparatively little heat. In 

 contradistinction to the rich limes, however, they set rapidly in the 

 open air, and permanently under water ; for which reasons they alone 

 should be used for exposed or submerged walls. Artificial hydraulic 

 limes are made by the addition of clay, containing soluble silicate of 

 alumina, to the pure carbonate of lime, and by calcining those mate- 

 rials together ; or it is made by the addition of pounded and rather 

 under-burnt brick or tile-dust to the mortar of rich limes. The arti- 

 ficial hydraulic limes obtained by the simultaneous calcination of the 

 lime and clay are, it may be observed, much more fitted to resist the 

 solvent action of running waters, than those in which no pyrogeuous 

 combination takes place between those elements. 



The common chalk lime of the neighbourhood of London may be 

 considered to represent the type of the rich limes ; some of the impure 

 oolitic stones yield the decidedly poor limei ; and the blue lias lime 

 maybe taken to represent the type of the hydraulic limes; the so- 

 called yraij stone lime of London is simply a moderately hydraulic 

 lime ; whilst strictly speaking, the Portland cement ought to be con- 

 sidered an eminently hydraulic artificial lime [PORTLAND CEMENT]. 

 The gray stone lime is obtained from the basement beds of the chalk ; 

 and the blue lias lime from the formation of that name. The Romans 

 seem to have used pounded brick dust for the purpose of making 

 artificial hydraulic limes, whenever they could not obtain puzzuolanos, 

 or similar volcanic silicates of alumina; and the modern engineers 



