470 PRINCIPLES OF CHEMISTRY 



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 bleaching 

 property of chlorine 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, &c. 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 application 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 

 carbon, it decomposes hydrocarbons (and many of their derivatives) at 

 a high temperature, depriving them of their hydrogen and liberating 

 the carbon, as, for example, is clearly seen when a lighted candle is 

 placed in a vessel containing chlorine. The flame becomes smaller, but 



19 Ozone and peroxide of hydrogen also bleach tissues. As the action of peroxide ol 

 hydrogen is easily controlled by taking a weak solution, and as it has hardly any action 

 upon the tissues themselves, it is replacing chlorine more and more as a bleaching agent. 

 The oxidising property of chlorine is apparent in destroying the majority of organic 

 tissues, and proves fatal to organisms. This action of chlorine is taken advantage of in 

 quarantine stations. But the simple fumigation by chlorine must be 'carried on with 

 great care in dwelling places, because chlorine disengaged into the atmosphere renders 

 it harmful to the health. 



20 A certain propensity of carbon to attract chlorine is evidenced in the immense 

 absorption of chlorine by charcoal (Note 7), 'but, so far as is at present known (if I am 

 not mistaken, no one has tried the aid of light), no combination takes place between the 

 chlorine and carbon. 



