SODA

Caustic soda ( Hydrate de soude , Fr.; Aetznatron , Germ.); is an alkaline substance, used in chemical researches, in bleaching, and in the manufacture of soap. It is prepared by boiling a solution of crystallized carbonate of soda in 4 or 5 parts of water, with half its weight of recently slaked and sifted lime. At the end of half an hour, the ve el of iron, porcelain, or preferably silver, may be removed from the fire, and covered carefully, till the calcareous matter has settled into a solid magma at the bottom. The clear supernatant lye may be then decanted into bottles for use in the liquid state, or evaporated, out of contact of air, till it a umes an oily appearance, then poured upon an iron or marble slab, broken into pieces, and put up in phials secured with greased stoppers or corks. Caustic soda is a white brittle ma , of a fibrous texture, a specific gravity of 1·536, melting at a heat under redne , having a most corrosive taste and action upon animal matters, di olving readily in both water and alcohol, attracting carbonic acid when exposed to the atmosphere, but hardly any water, and falling thereby into an efflorescent carbonate; it forms soaps with tallow, oils, wax, rosin; di olves wool, hair, silk, horn, alumina, silica, sulphur, and some metallic sulphurets. It consists of 77·66 soda, and 22·34 water. A solution of caustic soda affords no precipitate with solution of chloride of platinum, or tartaric acid, as a solution of caustic potash never fails to do. The following Table of the quantity of Caustic Soda contained in Lyes of different densities, has been given by Richter :— | Spec. grav. | Soda per cent. | | 1·00 | 0·00 | | 1·02 | 2·07 | | 1·04 | 4·02 | | 1·06 | 5·89 | | 1·08 | 7·69 | | 1·10 | 9·43 | | 1·12 | 11·10 | | 1·14 | 12·81 | | 1·16 | 14·73 | | 1·18 | 16·73 | | 1·20 | 18·71 | | 1·22 | 20·66 | | 1·24 | 22·58 | | 1·26 | 24·47 | | 1·28 | 26·33 | | 1·30 | 28·16 | | 1·32 | 29·96 | | 1·34 | 31·67 | | 1·35 | 32·40 | | 1·36 | 33·08 | | 1·38 | 34·41 | Soda free from water, can be obtained only by the combustion of sodium , which see.