THE HALOGENS 469 



spending quantity of chlorine. Thus CCTC1 2 , NOC1, N0 2 C1, S0 2 C1. 4 , 

 fec., are obtained. They correspond with the hydrates CO(OH) 2 , 

 NO(OH), N0 2 (OH), S0 2 (OH) 2 , &c., and to the anhyhrides CO 2 , 

 N 2 3 , N 2 5 , S0 3 , &c. Here we should notice two aspects of the 

 matter : (1) chlorine combines with that with which oxygen is able to 

 combine, because it is in many respects equally if not more energetic 

 than oxygen and replaces it in the proportion Cl 2 : O ; (2) that highest 

 limit of possible combination which is proper to a given element or 

 grouping of elements is very easily and often attained by combination 

 with chlorine. If phosphorus gives PC1 3 and PC1 5 , it is evident that 

 PC1 5 is the higher form of combination compared with PC1 3 . To the 

 form PC1 5 , or in general PX 5 , correspond PH 4 I, PO(OH) 3 , POC1 3 , &c. 

 If chlorine does not always directly give compounds of the highest 

 possible forms for a given element, then generally the lower forms 

 combine with it in order to reach or approach the limit. This is 

 particularly clear in hydrocarbons, where we see the limit C w H 2n+a 

 very distinctly. The unsatu rated hydrocarbons are sometimes able to 

 combine with chlorine with the greatest ease and thus reach the limit. 

 Thus ethylene, C 2 H 4 , combines with C1 2 , forming the so-called Dutch 

 liquid or ethylene chloride, C 2 H 4 C1 2 , because it then reaches the limit 

 C n X 2n+ .2*. In this and all similar cases the combined chlorine is able by 

 reactions of substitution to give a hydroxide and a whole series of other 

 derivatives. Thus a hydroxide called glycol, C 2 H 4 (OH) 2 , is obtained 

 from C 2 H 4 C1 2 . 



Chlorine in the presence of water very often acts directly as an 

 oxidising agent. A substance A combines with chlorine and gives, for 

 example, AG1 2 , and this in turn a hydroxide, A(OH) 2 , which on losing 

 water forms AC. Here the chlorine has oxidised the substance A. This 

 frequently happens in the simultaneous action of water and chlorine : 

 A + H 2 O + C1 2 = 2HC1 4- AO. Examples of this oxidising action of 

 chlorine may frequently be observed both in practical chemistry and 

 technical processes. Thus, for instance, chlorine in the presence of 

 water oxidises sulphur and metallic sulphides. In this case the 

 sulphur is converted into sulphuric acid, and the chlorine into hydro- 

 chloric acid, or a metallic chloride if a metallic sulphide be taken. A 

 mixture of carbonic oxide and chlorine passed into water gives carbonic 

 anhydride and hydrochloric acid. Sulphurous anhydride is oxidised 

 by chlorine in the presence of water into sulphuric acid, just as it ia 

 by the action of nitric acid : S0 2 + 2H 2 O + C1 2 = H 2 SO 4 + 2HC1. 



The oxidising action of chlorine in the presence of water is taken 

 advantage of in practice for the rapid bleaching of tissues and fibres. 

 The colouring matter of the fibres is altered by oxidation and con- 



