§ 106. =Caustic Soda--Sodium Hydrate= (NaHO).--This substance is a white solid, very similar in appearance to potassium hydrate; it absorbs moisture from the air, and afterwards carbon dioxide, becoming solid again, for the carbonate is not deliquescent. In this respect, then, there is a great difference between potash and soda, for the former is deliquescent both as hydrate and carbonate; a stick of potash in a semi-liquid state, by exposure to the air, continues liquid, although saturated with carbon dioxide. Pure sodium hydrate has a specific gravity of 2·0; it dissolves in water with evolution of heat, and the solution gives all the reactions of sodium hydrate, and absorbs carbon dioxide as readily as the corresponding solution of potash. The _liquor sodæ_ of the B.P. should contain 4·1 per cent. of NaHO. § 107. =Sodæ Carbonas--Carbonate of Soda=--(Na₂CO₃10H₂O).--The pure carbonate of soda for medicinal use is in colourless and transparent rhombic octahedrons; when exposed to air, the crystals effloresce and crumble. The _sodæ carbonas exsiccata_, or dried carbonate of soda, is simply the ordinary carbonate, deprived of its water of crystallisation, which amounts to 62·93 per cent. § 108. =Bicarbonate of Soda= (NaHCO₃) occurs in the form of minute crystals, or, more commonly, as a white powder. The _liquor sodæ effervescens_ of the B.P. is a solution of the bicarbonate, 30 grains of the salt in 20 ozs. of water (3·45 grms. per litre), the water being charged with as much carbonic acid as it will hold under a pressure of seven atmospheres. _The bicarbonate of soda lozenges_ (_trochisci sodæ bicarbonatis_) contain in each lozenge 5 grains (327 mgrms.) of the bicarbonate. The carbonate of soda sold for household purposes is of two kinds--the one, “seconds,” of a dirty white colour and somewhat impure; the other, “best,” is a white mass of much greater purity. _Javelle water_ (_Eau de Javelle_) is a solution of hypochlorite of soda; its action is poisonous, more from the caustic alkali than from the chlorine, and may, therefore, be here included. § 109. =Statistics.=--Poisoning by the fixed alkalies is not so frequent as poisoning by ammonia. Falck has collected, from medical literature, 27 cases, 2 of which were the criminal administering of _Eau de Javelle_, and 5 were suicidal; 22, or 81·5 per cent., died--in 1 of the cases after twenty-four hours; in the others, life was prolonged for days, weeks, or months--in 1 case for twenty-seven months. In the ten years 1883-1892, in England and Wales, there were 27 deaths from poisoning by the fixed alkalies; 2 were suicidal (1 from potash, the other from soda); the remaining 25 were due to accident; of these, 7 (3 males and 4 females) were from caustic soda, and 18 (8 males and 10 females) from caustic potash.