SODIUM CHLORIDE -"BERTH OLLET'S LAWS 457 



temperature^ &c., as was shown in the preceding portions of this chapter, 

 and as will be frequently found hereafter. 



If hydrochloric acid enters into double decomposition with basic 

 oxides and their hydrates, this is only .due to its acid properties ; and 

 for the same reason it rarely enters into double decomposition with 

 acids and acid anhydrides. Sometimes, however, it combines with the 

 latter, as, for instance, with the anhydride of- sulphuric acid, forming 

 the compound S0 3 HC1 ; and in other cases it acts on acids, giving up 

 its hydrogen to their oxygen and forming chlorine, as will be seen in 

 the following chapter. 



Hydrochloric acid, as may already be concluded from the compo- 

 sition of its molecule, belongs to the monobasic acids, and does not, 

 therefore, give true acid salts (like HNaSO 4 or HNaCO 3 ) ; nevertheless 

 many metallic chlorides, formed from powerful bases, are ca'pable o_i 

 combining with hydrochloric acid, just as they combine with water, of 

 with ammonia, or as they give double salts* Compounds have long 

 been known of hydrochloric acid with auric, platinic, and antimonious 

 chlorides, and other similar metallic chlorides corresponding with very 

 feeble bases. But Berthelot, Engel, and others have shown that the 

 capacity of HC1 for combining with M H C1 OT is much more frequently 

 encountered than was previously supposed. Thus, for instance, dry hydro- 

 chloric acid when passed into a solution of zinc. chloride (containing an 

 excess of the salt) gives in the cold (0) a compound HCl,ZnCl 2 ,2H 2 O, 

 and at the ordinary temperature HCI,2ZnCi 2 ,2H 2 O, just as it is able at 

 ,low temperatures to form the crystallo-hydrate ZnCl 2 ,3H 2 O (Engel, 

 1 886). Similar compoundsare obtained with CdCl 2 ,CuCl 2 , HgCl 2 ,Fe 2 Cl 6| 

 <fec. (Berthelot, ,Ditte, Cheltzoff, LachinofF, and others). These com- 

 pounds with hydrochloric acid are generally more soluble in water than 

 the metallic chlorides themselves, so that whilst hydrochloric acid 

 decreases the solubility of M M Cl OT , corresponding with energetic bases (for 

 instance, sodium or barium chlorides), it increases the solubility of the 

 metallic chlorides corresponding with feeble bases (cadmium chloride t 

 ferric chloride, fec.) Silver chloride, which is insoluble in water, is soluble 

 in hydrochloric acid. Hydrochloric acid also combines with certain un- 

 saturated hydrocarbons (for instance, with turpen tine, Ci Hi 6 ,2HCl) and 

 their derivatives. Sal-ammoniac, or ammonia hydrochloride, NH 4 C1 

 a= NH 3 ,HC1, also belongs to this class of compounds. 43 If hydrogen 

 chloride gas be mixed with ammonia gas a solid compound consisting 



45 When an uneaturated hydrocarbon, or, in general, an uiisaturated compound^ 

 assimilates to itself the molecules C1 2 , HC1, S0 3 , H 2 SO 4 , &c., the cause of the reaction 

 is most simple. As nitrogen, besides the type NX 3 to which NH 3 , belongs, gives com- 

 pounds of the type NXy for example, N0 2 (OH) the formation of ths salts cf 



