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8. It was desirable to have a test for these impurities, as well as 

 an easy and effectual mode of removing the last traces of them ; 

 especially as many sorts of chloroform, not made here, were far in- 

 ferior in quality to that prepared in Edinburgh. One very deli- 

 cate test is, that oil of vitriol, which should be quite colourless and 

 pure (as it may be rendered by Mr Kemp's process, lately read to 

 the Society), when agitated with the chloroform, becomes yellow or 

 brown, from its action on the oils, which it chars and destroys. Any 

 change of colour is easily seen by the contrast with the colourless 

 chloroform which floats above. Pure chloroform gives no colour to 

 the acid. It is essential that the oil of vitriol be colourless, and 

 also of full density ; for, if coloured, it is not easy to see a slight 

 change in its colour ; and if below the proper density, that is, too 

 weak, it is not much coloured by a chloroform which will render 

 brown the acid of proper strength. 



9. Another test, still more delicate, I find to be the smell of the 

 oils. When chloroform is poured on the hand or a handkerchief it 

 rapidly evaporates ; but the oils, being less volatile, are left behind, 

 and their smell, previously covered by that of the chloroform, is 

 easily recognised. Until very lately, no chloroform was sold, or, 

 indeed, known, which would stand this test, or even the former. 



10. Up to 1849, the best commercial chloroform had a specific 

 gravity of 1"480, which was considered a guarantee of its purity. 

 But it had been obtained, by chemists, of specific gravity 1-494 and 

 even 1'497. I have found that chloroform of 1480, when once 

 more acted on by oil of vitriol, which destroys the oils and becomes 

 brown, may be obtained, after removing the sulphurous acid, of spe- 

 cific gravity 1-500 at 60°. This I take to be the specific gravity 

 of pure chloroform. Our best makers have lately, much to their 

 credit, pushed the purification so far as to furnish chloroform even 

 of this highest density, and also, in other respects, such as it ought 

 to be. 



11. There are still, however, many makers, in other places, 

 whose chloroform is not so pure ; and I shall now describe the 

 method which, with Mr Kemp, I have employed for purifying, per- 

 fectly and easily, any commercial chloroform (except one remarkable 

 specimen, of which more hereafter), a process which will enable any 

 medical man to purify it for himself with the greatest facility. 



12. The chloroform, having been tested as above, and found more 



