~Physical properties.~ Bismuth is a heavy, crystalline, brittle metal nearly the color of silver, but with a slightly rosy tint which distinguishes it from other metals. It melts at a low temperature (270 deg.) and has a density of 9.8. It is not acted upon by the air at ordinary temperatures. ~Chemical properties.~ When heated with the blowpipe on charcoal, bismuth gives a coating of the oxide Bi_{2}O_{3}. This has a yellowish-brown color which easily distinguishes it from the oxides formed by other metals. It combines very readily with the halogen elements, powdered bismuth burning readily in chlorine. It is not very easily acted upon by hydrochloric acid, but nitric and sulphuric acids act upon it in the same way that they do upon copper. ~Uses.~ Bismuth finds its chief use as a constituent of alloys, particularly in those of low melting point. Some of these melt in hot water. For example, Wood's metal, consisting of bismuth, lead, tin, and cadmium, melts at 60.5 deg.. ~Compounds of bismuth.~ Unlike the other elements of this group, bismuth has almost no acid properties. Its chief oxide, Bi_{2}O_{3}, is basic in its properties. It dissolves in strong acids and forms salts of bismuth: Bi_{2}O_{3} + 6HCl = 2BiCl_{3} + 3H_{2}O, Bi_{2}O_{3} + 6HNO_{3} = 2Bi(NO_{3})_{3} + 3H_{2}O. The nitrate and chloride of bismuth can be obtained as well-formed colorless crystals. When treated with water the salts are decomposed in the manner explained in the following paragraph. HYDROLYSIS Many salts such as those of antimony and bismuth form solutions which are somewhat acid in reaction, and must therefore contain hydrogen ions. This is accounted for by the same principle suggested to explain the fact that solutions of potassium cyanide are alkaline in reaction (p. 210). Water forms an appreciable number of hydrogen and hydroxyl ions, and very weak bases such as bismuth hydroxide are dissociated to but a very slight extent. When Bi^{+++} ions from bismuth chloride, which dissociates very readily, are brought in contact with the OH^{-} ions from water, the two come to the equilibrium expressed in the equation Bi^{+++} + 3OH^{-} <--> Bi(OH)_{3}. For every hydroxyl ion removed from the solution in this way a hydrogen ion is left free, and the solution becomes acid in reaction. Reactions of this kind and that described under potassium cyanide are called _hydrolysis_. DEFINITION: _Hydrolysis is the action of water upon a salt to form an acid and a base, one of which is very slightly dissociated._ ~Conditions favoring hydrolysis.~ While hydrolysis is primarily due to the slight extent to which either the acid or the base formed is dissociated, several other factors have an influence upon the extent to which it will take place. 1. _Influence of mass._ Since hydrolysis is a reversible reaction, the relative masses of the reacting substances influence the point at which equilibrium will be reached. In the equilibrium