THE TAR ACIDS. 
§ 237-1 
191 
ammonium chloride, a few drops of the sample to be tested are added. 
In the presence of carbolic acid, a rose-red, blood-red, or red-brown tint 
is produced, according to the quantity present. Carbolic acid may be 
confounded with cresol or with creasote, but the distinction between pure 
carbolic acid, pure cresol, and creasote is plain. 
.OH 
§ 237. Cresol (Cresylic Acid, Methyl-phenol), C 6 H 4 <( .—There 
X CH 3 
are three cresols—ortho-, meta-, and para-. Ordinary commercial cresol 
is a mixture of the three, but contains little ortho-cresol; the more 
important properties of the pure cresols are set out in the following 
table. Pure ortho-, meta-, and para-cresol have been obtained by syn¬ 
thetical methods ; they cannot be said to be in ordinary commerce. 
Melting-point. 
Boiling-point. 
Converted by fusion 
with Potash into— 
Ortho- 
31-31-5° C. 
188-0° 
Salicylic acid 
(Ortho -0 xy benzoic 
acid). 
Meta- . . 
1 
Fluid at ordinary 
temperature. 
201-0° 
Meta -0 xy benzoic 
acid. 
Para- . . 
36° 
198° 
Para-oxybenzoic acid. 
Commercial cresol is at ordinary temperatures a liquid, and 
cannot be obtained in a crystalline state by freezing. Its boiling-point 
is from 198° to 203° ; it is almost insoluble in strong ammonia, and, 
when 16 volumes are added, it then forms crystalline scales. On the 
other hand, carbolic acid is soluble in an equal volume of ammonia, 
and is then precipitated by the addition of 1J volume of water. Cresol 
is insoluble in small quantities of pure 6 per cent, soda solution ; with 
a large excess, it forms crystalline scales ; while carbolic acid is freely 
soluble in small or large quantities of alkaline solutions. 
Cold petroleum spirit dissolves cresol, but no crystalline scales can 
be separated out by a freezing mixture. Carbolic acid, on the contrary, 
is but sparingly soluble in cold petroleum, and a solution of carbolic 
acid in hot petroleum, when exposed to sudden cold produced by a 
freez : ng mixture, separates out crystals from the upper layer of liquid. 
Cresol is miscible with glycerin of specific gravity 1-258 in all propor¬ 
tions ; 1 measure of glycerin mixed with 1 measure of cresol is com¬ 
pletely precipitated by 1 measure of water. Carbolic acid, under 
the same circumstances, is not precipitated. The density of cresol is 
about 1-044. It forms with bromine a tri-bromo-cresol, but this is 
liquid at ordinary temperatures, while tri-bromo-phenol is solid. On 
