218 M. Oay-Lussac on the Chloride of Lime. [Sept. 



reputation to lose ; responsibility is thus shuffled from both, 

 and rests on neither. Such, however, are the people who by- 

 unaccountable prescription supply the city of London, and the 

 philosophers of England, with the instruments which Mr. 

 Daniell so well describes. 



If common notoriety did not bear Mr. Daniell out in his as- 

 sertions, the shameful disagreement of the thermometers used 

 by Captain Parry in his last voyage, would fully do so. On 

 one occasion this amounted to no less than 13 degrees ; Capt. 

 Parry could do nothing else than give a mean, though in such 

 a case — 48° had as good a chance of being the truth as — 

 35°. X. 



Article XII. 



Instructions for the Assay of Chloride of Lime. 

 By M. Gay-Lussac* 



The uncertainty which has hitherto existed in the modes of 

 ascertaining the quality, and consequently the commercial value 

 of chloride" of lime, and in no small degree retarded its coming 

 into general use, has determined me to publish the following- 

 instructions on the subject. I shall divide the work into two 

 parts ; in the first 1 shall expose the principles on which the 

 assay of the chloride of lime is founded, and in the second I 

 shall describe the instrument which I call a Chlorometer, and the 

 manipulations necessary for making the assay with sufficient 

 accuracy for the purposes of those arts in which chlorine is 

 employed. 



Part I. 



Principles on which the Assay of Chloride of Lime by means of 



Indigo is founded. 



■ It is known that chlorine destroys vegetable colours, by form- 

 ing new compounds with their component principles. It is in 

 consequence of this property which it possesses, whether in the 

 state of gas, in solution in water, or in combination with an 

 alcali, that it is employed in the arts of bleaching, calico print- 

 ing, &c. The same 'quantity of chlorine, in either of those 

 three states, destroys the same quantity of colouring matter ; and 

 since by combination with an alcali, it becomes fixed, has 

 scarcely any smell, keeps better, is more portable, and more 

 capable of concentration, the advantages of preparing it in that 

 form are obvious. 



Caustic potash, soda and lime, and even their carbonates, 

 combine very readily with chlorine. Its combination with the 



* From the Annales de C'himie. 



