748 SACCHARINE SUBSTANCES. 



water, and the solution generally filtered hot through a bed of 

 animal charcoal in grains like gunpowder, and about two feet 

 in thickness. The colourless syrup thus obtained is evaporated 

 in vacuo, about 150, in close pans heated by steam, from 

 which the vapour is constantly withdrawn by an air-pump. 

 When sufficiently concentrated, the syrup is run into a cooler, 

 and agitated by an oar to promote its granulation. 



It is then transferred into moulds, which are inverted cones, 

 having an aperture in the apex, and kept in a warm place, while 

 the dark coloured and uncrystallizable syrup drains off; a strong 

 syrup of pure sugar being poured on the upper surface to per- 

 colate downwards and remove the last portions of the former. 

 Instead of the pure syrup, moist pipe-clay was formerly placed 

 on the surface of the sugar for the same purpose, and is still 

 employed in clayed sugars. The loaf sugar from these moulds 

 is a white compact mass, composed of small crystals. A strong 

 solution of it, evaporated slowly, affords large transparent and 

 colourless crystals of sugar-candy, of which the form is an 

 oblique prism of a square base, or a six-sided prism with dihedral 

 summits. The density of pure sugar is 1.5629 (Thomson). 



Loaf sugar diffuses a phosphorescent light when broken in the 

 dark. It is unalterable in dry air, and loses nothing but a trace 

 of hygroscopic water when heated. It fuses at 356 (1 80 cent.) 

 and forms a thick tenacious liquid, which becomes a transparent 

 vitreous mass on cooling (barley- sugar). The latter changes 

 after a time, and rapidly when damp, into an opaque mass, 

 which exhibits when broken, the crystalline facets of ordinary 

 sugar. Sugar is soluble in one third of its weight of cold, and 

 in all proportions of boiling water. Its power to crystallise 

 is destroyed by keeping its solution for some time boiling, and 

 also by the addition of 2 T th of its weight of oxalic, citric, or 

 malic acid, which instantly render a viscid and boiling syrup, 

 very fluid. Sugar dissolves in 80 parts of absolute alcohol at 

 the boiling temperature, very slightly in the same cold, in 

 4 parts of alcohol of density 0.830, and is wholly insoluble in 

 ether, which precipitates sugar from its solutions. Sugar is 

 nutritive when accompanied with other aliments, but is inca- 

 pable alone of supporting life for any length of time, in common 

 with all organic principles destitute of nitrogen. A solution of 

 sugar placed in contact with the stomach of the calf (rennet), 



