asserts that he has conquered this difficulty, and additionally perfected a machine for measuring the current used in the electric light. He states that it consists of an apparatus placed in every house lighted by electricity, which registers the quantity of electricity consumed, and uses for the purpose 1000th part of the quantity employed in the building.
Dr Siemens, no mean authority, doubts the practicability of applying electric lighting to household illumination.
A matter of primary importance in connection with the successful working of the electric light is the quality of the carbon points. In their manufacture gas carbon obtained from the necks of the retorts used in gas-making, as being the hardest and purest, is employed.
Superior, however, as this form of carbon is to every other description of the substance, it is never chemically pure, and as any foreign substance imparts to the light the irregularity or flickering that sometimes accompanies it, it is necessary the impurities should be removed. To effect their separation the carbon has to undergo several processes, such as soaking in caustic potash to remove the silica, treatment with strong acids, several washings, grinding, &c. It is then kneaded and put into moulds, in which it is subjected to a pressure as high as 12 tons to the square foot. Subsequently the points so made are baked.
LIGHTNING. See Accidents.
LIG′NIN. C6H10O5. Syn. Cellulose. This is woody fibre deprived of all foreign matter. It forms about 95 per cent. of baked wood, and constitutes the woody portion of all vegetable substances. Fine linen and cotton are almost entirely composed of lignin, the associated vegetable principles having been removed by the treatment the fibres have been subjected to during the process of their manufacture.
Pure lignin is tasteless, inodorous, insoluble in water and alcohol, and absolutely innutritious; dilute acids and alkaline solutions scarcely affect it, even when hot; oil of vitriol converts it into dextrin or grape sugar, according to the mode of treatment. When concentrated sulphuric acid is added very gradually to about half its weight of lint, linen rag, or any similar substance shredded small, and contained in a glass vessel, with constant trituration, the fibres gradually swell up and disappear, without the disengagement of any gas, and a tenacious mucilage is formed, which is entirely soluble in water. If, after a few hours, the mixture be diluted with water, the acid neutralised by the addition of chalk, and, after filtration, any excess of lime thrown down by the cautious addition of a solution of oxalic acid, the liquid yields, after a second filtration, and the addition of alcohol in considerable excess, a gummy mass, which possesses
all the characters of pure dextrin. If, instead of at once saturating the diluted acid solution with chalk, we boil it for 4 or 5 hours, the dextrin is entirely converted into grape sugar, which, by the addition of chalk and filtration, as before, and evaporation by a gentle heat to the consistence of a syrup, will, after repose for a few days, furnish a concrete mass of crystallised sugar. By strong pressure between folds of porous paper or linen, redissolving it in water, agitation with animal charcoal, and recrystallisation, brilliant colourless crystals of grape sugar may be obtained. Hemp, linen, or cotton, thus treated, yield fully their own weight of gum, and 1 per cent. of their weight of grape sugar. During the above transformation, the sulphuric acid is converted into sulpholignic acid, and may be procured in a separate state. A solution of oxide of copper in ammonia, or solution of basic carbonate of copper in strong ammonia, dissolves cotton, which may then be precipitated by acids in colourless flakes.
LIG′NITE. Syn. Brown coal. Wood and other matter more or less mineralised and converted into coal. The lignites are generally dark brown, and of obvious woody structure. They are distinguished from true coals by burning with little flame and much smoke. Those of Germany are largely used as a source of paraffin and burning oils.
LIG′NUM VI′TÆ. See Guaiacum Wood.