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Selected Articles. 
be discovered in water which has been employed to wash 
common street gas, by saturating it with muriatic acid, and 
dipping into it a stick of fir. A purple red colour is occa- 
sioned. 
Pyrrol forms the principal constituent of empyreumatic 
ammonia, and when its peculiar smell is known, it may be 
distinguished among the odours which are disengaged by the 
distillation of bones and horns. Pyrrol is also contained in 
tobacco oil. 
ACIDS. 
1. Carbolic Acid. 
This acid is a colourless oily substance, sinking in water. 
Its smell is extremely empyreumatic ; it is caustic and burn- 
ing, and has a strong action on the skin. When the skin is 
rubbed with it a feeling of burning is felt, and a white spot is 
produced, which on being touched with water becomes red, 
and in some days desquamates. In this respect it corresponds 
with creosote, but differs in being acid ; in being precipitated 
by acetate of lead, and in not being altered by ammonia or 
the atmosphere, and in being converted by nitric acid even 
diluted into a reddish brown matter. 
Carbolic acid dissolves in water. The solution is colour- 
less and the acid is easily rendered conspicuous with nitric 
acid. The water is at first yellow or orange, and afterwards 
reddish brown ; a stick of fir plunged in dilute carbolic acid, 
takes after being moistened w 7 ith muriatic acid in half an 
hour, a blue colour. The vapour of muriatic acid also 
tinges shavings moistened with carbolic acid of a blue co- 
lour. This tinge withstands the action of chlorine in a high 
degree. 
The salts of carbolic acid are colourless, and many of 
them can be crystallized; their aqueous solutions present the 
same appearances with fir as the solution of carbolic acid. 
Carbolic acid precipitates albumen, prevents organic sub- 
stances from putrefying, and removes the putrid smell of meat 
when digested with an aqueous solution, much better than 
chlorine. The presence of carbolic acid may be detected in 
