PREPARATION AND PROPERTIES OF CHLORINE. 89 



ciated together, entering into the composition of different salts, 

 in the waters of the ocean, from which source they are alt 

 [more or less directly] obtained ; Chlorine, on account of the 

 important use of some of its compounds in the arts and manu- 

 factures, Iodine and Bromine, chiefly for the purposes of phi- 

 losophical chemistry. 



" As I purpose to combine a certain degree of systematic 

 arrangement in my present course of lectures on Chemistry, 

 with an endeavour to bring the subjects of science { home to 

 your business and bosoms/ by explaining the chemical history 

 of those substances and processes which are of most import- 

 ance to us all, I shall now introduce the consideration of 

 Chlorine, Iodine, and Bromine, in order to complete our 

 view of the bodies termed by chemists Supporters of Com- 

 bustion." * 



The discovery of CHLORINE and the changes of opinion as 

 to its nature were then briefly related, and a quantity of the gas 

 prepared on the lecture-table from a mixture of oxide of manga- 

 nese and muriatic acid, contained in a retort, and heated by the 

 lamp-furnace ; the chlorine being received, as usual, in vessels 

 standing on the shelf of the pneumatic trough, but over warm 

 water, because cold water absorbs the gas. The theory of this 

 mode of obtaining chlorine being deferred, because it could not 

 well have been understood without a previous knowledge of 

 several subjects not yet examined, the principal properties of 

 the gas were pointed out and exhibited ; especially its greenish 

 colour, its irrespirable nature (in which it so eminently differs 

 from the supporter of combustion previously examined, Oxy- 

 gen), its great weight or specific gravity (2-| times that of atmo- 

 spheric air), and its characters as a supporter of combustion. 

 In illustrating these characters, phosphorus, and the alkaline 

 metal potassium were severally burnt in the gas, the phos- 

 phorus taking fire spontaneously, on immersion in it, and be- 



* It was the wish of the Conductors of the Schools that the attention of 

 their pupils, in the study of Chemistry, should be directed, chiefly, to the 

 chemical history of those principles and processes, both of nature and of the 

 arts, which are of universal interest and notoriety. But as, in the opinion 

 of the Teacher, it was equally important to the success of the Department, 

 as a branch of General Education, to enter upon the consideration of those 

 subjects, in a truly scientific manner, he endeavoured to combine the object 

 of the Conductors with his own, by adopting an arrangement which might 

 admit of the attainment of both. Thus, in the Course above detailed, the 

 subjects of pure science considered, comprising the Supporters of Combus- 

 tion, Pneumatic Chemistry, the Simple Non-metallic Combustibles, and 

 Combustion itself, were blended with the chemical history of atmospheric 

 air, respiration, water, and the different kinds of fuel. A corresponding 

 arrangement was adopted for the Lectures on Organic Chemistry subse- 

 quently delivered. 



