464 PKINCIPLES OF CHEMISTRY 



and hydrochloric acid. Sulphurous anhydride is oxidised by 

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

 by the action of nitric acid: SO 2 + 2H 2 O + Cl a =H 2 SO 4 + 2HCl. 

 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- 

 verted into a colourless substance, but the chlorine afterwards 

 acts on the tissue itself. Bleaching by means of chlorine therefore 

 requires a certain amount of technical skill in order that the chlorine 

 should not act on the fibres themselves, but that its action should be 

 limited to the colouring matter only. The fibre for making writing 

 paper, for instance, is bleached in this manner. The property of 

 chlorine of bleaching was discovered by Berthollet, and forms an 

 important acquisition to the arts, because it has in the majority of 

 cases replaced that which before was the universal method of bleach- 

 ing, namely, exposure to the sun of the fabrics damped with water, 

 which is still employed for linens, <fcc. Time and great trouble, and 

 therefore money also, have been considerably saved by this change. 19 



The power of chlorine for combination is intimately connected with 

 its capacity for substitution, because, according to the law of substitu- 

 tion, if chlorine combines with hydrogen, then it also replaces hydrogen, 

 and furthermore the combination and substitution are accomplished in 

 the same quantities. Therefore the atom of chlorine which combines 

 with the atom of hydrogen is also able to replace the atom of hydrogen. 

 We mention this property of chlorine not only because it illustrates 

 the adaptation of the law of substitution in clear and historically 

 important examples, but more especially because reactions of this kind 

 explain those indirect methods of the formation of many substances 

 which we have often mentioned and to which recourse is had in many 

 cases in chemistry. Thus chlorine does not act on carbon, 20 oxygen, 

 or nitrogen, but nevertheless its compounds with these elements may 

 be obtained by the indirect method of the substitution of hydrogen 

 by chlorine. 



As chlorine easily combines with hydrogen and does not act on 



19 The oxidising property of chlorine shows itself when it destroys the majority of 

 organic tissues, and proves fatal to organisms. This property of chlorine is taken 

 advantage of in quarantine stations. But the simple fumigation by chlorine must !>< 

 carried on with great care in dwelling places, because chlorine disengaged into the 

 atmosphere renders it harmful to the health by attacking the respiratory organs and the 

 tissues of the lungs. 



20 A certain propensity of carbon to attract chlorine must be seen in the immense 

 absorption of chlorine by charcoal (Note 7), but, as far as is at present known (no one 

 has tried, if I do not mistake, to have recourse to the aid of light), no combination thjen 

 takes place between the chlorine and carbon. 



