330 
ON THE PURIFICATION OF CHLOROFORM. 
of such chloroform, which was the best anywhere made. I 
must add, however, that the quantity of oils in the chloro- 
form of the best Edinburgh manufacturers although variable 
within certain limits, was always so small, that that product 
was fit for use, and only caused headache, &c, in a few pe- 
culiarly sensitive persons. 
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 inferior in quality to that prepared in 
Edinburgh. One very delicate test is, that of oil of vitriol, 
which should be quite colourless, pure, and of the full den- 
sity of 1.840 at least, as it may be obtained by Mr. Kemp's 
process, lately read to the Royal Society; when agitated 
with the chloroform, it becomes yellow or brown, from its 
action on the oils, which it chars and destroys. Any change 
of colour is easily seen by contrast with the colourless chlo- 
roform which floats above. Pure chloroform gives no co- 
lour 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 on its colour ; and if below the 
proper density, that is too weak, it is not much coloured by 
a chloroform which will render dark brown the acid of pro- 
per strength. 
9. Another test, still more delicate, I find to be the smell 
of the oils. When chloroform is poured on the hand or on 
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 spe- 
cific gravity 1.494, and even 1.497. I have found that chlo- 
roform of 1.480, when once more acted on by oil of vitriol, 
