REMARKS ON TI1E ACIDS OF THE BRITISH PHARMACOPOEIA. 19 
of potash, whereby a white crystalline magma is obtained. This is dissolved 
in hot water; the oil which rises to the surface is rejected, and the lower alka¬ 
line liquid is neutralized with hydrochloric acid. The carbolic acid separates, 
and is washed, dried, rectified by distillation, and crystallized by freezing. 
This substance melts at 95° and boils at 869° Fahr. By exposure to the air, 
the crystals absorb moisture and liquefy. It closely resembles cresylic acid, an 
allied body obtained from tar, and now found in commerce. It may be distin¬ 
guished by its boiling-point, cresylic acid boiling at 397° Fahr., 28 degrees 
higher. In characters and properties it is very like wood-creasote, for which, 
indeed, it is often substituted. It may be distinguished, however, by the fact 
that it has no action on polarized light, while creasote turns the plane of the 
ray to the right. Moreover creasote cannot be frozen. 
Carbolic acid has no action on litmus. Shaken with \ part of water and 
cooled to 40° Fahr., it forms a crystalline hydrate, 2C 6 H (i O,2HO. Treated 
with strong nitric acid, it yields carbozotic acid (picric acid or trinitrophenic acid). 
C 6 H 6 O+3 H N 0 3 = C 0 H 3 (N Go) 0 3 + 3 H 2 O. 
Carbolic acid. Picric acid. 
Acidttm Citricum.—T his acid is now represented with twice the quantity 
of water of crystallization assigned to it in the previous edition of the Pharma¬ 
copoeia. The present formula, H 3 C () H 5 0 7 , FLO, is undoubtedly the correct 
one, and represents the acid of commerce. When a solution of the acid under¬ 
goes spontaneous evaporation, the well-known right rhombic prisms are ob¬ 
tained, and these crystals have the composition expressed by the formula now 
given. But when crystallization takes place at the boiling temperature, crystals 
of a differerent shape are obtained, containing only half a molecule of water. 
These are represented by 2 (H 3 C 6 H 5 0 7 ),H 2 O, which was the composition as¬ 
signed to the acid in 1864. 
The process for citric acid is retained, but has been modified by omitting the 
fermentation of the lemon-juice by beer-yeast. The juice is at once heated 'to 
the boiling-point, and neutralized with chalk, whereby citrate of lime is preci¬ 
pitated. This salt, being less soluble in hot than in cold water, is more perfectly 
thrown down from a warm solution. 
2H 3 C 0 H 5 O 7 +3 CaC03= = Ca 3 (C, i H 5 0 7 ) 2 +3 H 2 0+3 C0 2 . 
Citrate of lime. 
The citrate of lime having been washed with hot water, .is decomposed with 
dilute sulphuric acid. The sulphate of lime having been removed by filtration, 
the liquid is evaporated to a density of 1-21, then cooled, and a further de¬ 
posit of sulphate of lime removed. The solution is again concentrated, and 
crystallized. 
Ca 3 (C 0 H 5 0 7 ) 2 + 3 H 2 S0 4 = 2 H 3 C g H 5 O r + 3 CaS0 4 . 
The presence of tartaric acid in citric acid may be detected by the addition 
of a solution of acetate of potash, which would give a crystalline precipitate with 
the former, but none with the latter. Citric acid, sparingly added to an excess 
of lime-water gives no precipitate in the cold, but a copious one on boiling. 
Seventy grains of the acid are neutralized by 1000 grain-measures of the 
volumetric solution of soda. Citric acid being tribasic,its atoms require 3 atoms 
of hydrate of soda for its saturation. 1000 grain-measures of the volumetric 
solution contain 1 atom in grains of hydrate of soda, and will therefore neu¬ 
tralize one-third of an atom in grains of citric acid, H 3 C 6 H 5 0 7 , H 2 0 = 210; 
one-third of which is 70. 
Acidum Gallicum.—V ery little change has been made in the description 
of this acid. The process stands unaltered, excepting that we are now told 
to dry the crystals at a “ temperature not exceeding 100°, ’ instead of 212°. 
The water of crystallization is entirely volatilized at the latter temperature, 
c 2 
