of the Elements. 437 



The four simple chlorides are all well known to chemists. 

 BCl^ is a dense gas. SiCl^, TiCl^, and SnCl^ are volatile fuming 

 liquids. These chlorides are obtainable by the direct action of 

 chlorine upon the elements, or upon a heated mixture of charcoal 

 and the anhydrides*. They are all soluble in excess of water, 

 undergoing a more or less complete decomposition. They all 

 combine directly with ammonia, to form, in all probability, chlo- 

 ride of ammonium, together with certain compounds of which 

 the formulae are not established. They all unite with alkaline 

 chlorides, forming double salts, such as — 



2NH'*C1 . BCl-* . Boro-chloride of ammonium. 

 2NH4C1 . SiCl" . Silico-chloride of ammonium. 

 2NH'*C1 . TiCl"* . Titano-chloride of ammonium. 

 2NH'*C1 . SnCl* . Stanno-chloride of ammonium. 

 2KC1 . SuCl'* . Stanno-chloride of potassium. 



The above formulfe of the tin salts are well established. The 

 other formulse are extremely probable from their analogy to those 

 of the fluorine compounds. 



The anhydrous boric, silicic, titanic, and stannic acids have 

 corresponding formulae, BO^ SiO^, TiO^, SnO^. The boric 

 compound is fusible at a full red heat into a transparent glass. 

 Silica, in the flame of the oxyhydrogen blowpipe, yields a trans- 

 parent glass. Titanic acid also requires the oxyhydrogen blow- 

 pipe to efi"ect its fusion. Stannic acid is an extremely refractory 

 body. All four compounds are very fixed ; that of boron, how- 

 ever, volatilizes slowly at an intense heat. Boric and silicic acids 

 volatilize i-eadily in the vapour of water. The anhydrides of 

 silicon, titanium and tin, are known to exist in several isomeric 

 modifications, distinguishable chiefly by their difi"erent behaviour 

 with solvents. Each of the four anhydrides, when fused with an 

 excess of carbonate of soda, displaces one atom of carbonic acid. 

 All four acids form anhydrosalts, those of silica being extremely 

 numerous and varied. Boric anhydride is always ready to assume 

 water and to dissolve in excess thereof. The other three anhy- 

 drides cannot be directly hydrated. Anhydrous stannic acid is 

 isomorphous with titanic acid or rutilc. Boric acid is soluble 

 in water, in acids, and in alkalies. One modification only of 

 silicic acid is, under certain conditions, soluble in all the above 



* When an excess of clilorine gas is passed over a heated mixture of 

 charcoal and stannic anhydride, chloride of tin and phosgene gas are 

 formed, according to the equation 



SnO'+2C + 8Cl=SnCl' + 2C CPO. 

 The pliosgene gas is always mixed with carhonic oxide, or with a great 

 excess of chlorine. The process is a very good one for the preparation of 

 chloride of tin. 



