178 POISONS : THEIR EFFECTS AND DETECTION. [§ 222. 
crystals is given variously by different authors : from our own observa¬ 
tion, the pure crystals melt at 40°-41°, any lower melting-point being 
due to the presence of cresylic acid or other impurity ; the crystals 
again become solid about 15°. Melted carbolic acid forms a colourless, 
limpid fluid, sinking in water. It boils under the ordinary pressure at 
182°, and distils without decomposition ; it is very readily and com¬ 
pletely distilled in a vacuum at about the temperature of 100°. After 
the crystals have been exposed to the air, they absorb water, and a 
hydrate is formed containing 16*07 per cent, of water. The hydrate 
melts at 17°; any greater hydration prevents the crystallisation of the 
acid ; a carbolic acid containing about 27 per cent, of water, and pro¬ 
bably corresponding to the formula C 6 H 6 0,2H 2 0, is obtained by gradually 
adding water to carbolic acid so long as it continues to be dissolved. 
Such a hydrate dissolves in 11*1 times its measure of water, and contains 
8*56 per cent, of real carbolic acid. Carbolic acid does not redden 
litmus, but produces a greasy stain on paper, disappearing on exposure 
to the air; it has a peculiar smell, a burning, numbing taste, and in the 
fluid state it strongly refracts light. Heated to a high temperature it 
takes fire, and burns with a sooty flame. 
When an aqueous solution of carbolic acid is shaken up with ether, 
benzene, carbon disulphide, or chloroform, it is fully dissolved by the 
solvent, and is thus easily separated from most solutions in which it 
exists in the free state. Petroleum ether, on the other hand, only 
slightly dissolves it in the cold, more on warming. Carbolic acid mixes 
in all proportions with glycerin, glacial acetic acid, and alcohol. It 
coagulates albumen, the precipitate being soluble in an excess of albumen ; 
it also dissolves iodine, without changing its properties. It dissolves 
many resins, and also sulphur, but, on boiling, sulphuretted hydrogen is 
disengaged. Indigo blue is soluble in hot carbolic acid, and may be 
obtained in crystals on cooling. Carbolic acid is contained in castoreum, 
a secretion derived from the beaver, but it has not yet been detected in 
the vegetable kingdom. The source of carbolic acid is at present coal- 
tar, from which it is obtained by a process of distillation. There are, 
however, a variety of chemical actions in the course of which carbolic 
acid is formed. 
§ 222. The common disinfecting carbolic acid is a dark reddish 
liquid, with a very strong odour ; at present there is very little phenol 
in it; it is mainly composed of meta- and para-cresol. It is official in 
Germany, and there must contain at least 50 per cent, of the pure 
carbolic acid. The pure crystallised carbolic acid is official in our own 
and all the Continental pharmacopoeias. In the British Pharmacopoeia, 
a solution of carbolic acid in glycerin is official; the proportions are 1 
part of carbolic acid and 4 parts of glycerin, that is, strength by measure = 
20 per cent. The Pharmacopoeia Germanica has a liquor natri carbolici 
