BITUMEN. 
453 
them all under the head of bitumen, giving naph- 
tha the preference, as being the most fluid and the 
least common. 
Naphtha is perfectly fluid and diaphanous ; it 
has a very strong smell, not much unlike the vola- 
tile oil of turpentine. It is rather unctuous to the 
touch, and so very light as to float on water. It 
catches fire very readily, and burns with a blueish 
flame and thick smoke till it is almost entirely con- 
sumed. 
It is the rarest of the bitumens, and is scarcely 
ever found in nature in a state of perfect purity : 
that which is used for commercial purposes is gene- 
rally adulterated with oil of turpentine. We are 
told, that in Persia it is more common than else- 
where, especially on the banks of the Caspian sea 
near Baku. The inhabitants of that neighbour- 
hood take advantage of the volatile and inflamma- 
ble vapour which rises from the earth where the 
naphtha is found, and kindle it to serve them as a 
natural fire for their culinary purposes. It is said 
also, that they employ it to burn their lime ; from 
which we may conclude that the vapour is very ac- 
tive. About six hundred yards round the place 
where these perpetual fires are burning, the people 
dig wells of thirty feet deep, where they collect the 
naphtha, which is not perfectly limpid, but of an 
amber colour. This is distilled, to extract the pure 
naphtha used in medicine. After the bitumen has 
undergone this process, there remains a blackish re- 
siduum, which serves the Persians to burn in their 
