REPORT ON THE PREPARATIONS OP GLACIAL ACETIC ACID. 1 S9 
plinric acid directed to be used is larger, being nearly twice tlie quantity. 
The specific gravity is required to be 1*065, 1 drachm requiring 97 measures 
of volumetric solution of soda for complete neutralization. Some minor de¬ 
tails of manipulation are omitted in this formula. 
The monohydrated acid of the United States Pharmacopoeia is prepared in 
a manner somewhat corresponding,—one equivalent of fused acetate of soda, 
with two equivalents of sulphuric acid, being the proportions demanded. 
The Prussian and Hanoverian Pharmacopoeias are the same in effect, but 
the process is slightly different, being performed by the agency of acid sul¬ 
phate of potash and acetate of soda, subjected to distillation, the specific 
gravity of the acid procured being from 1058 to 1080. But the process of 
M. Melsens is that which is now adopted on some parts of the Continent, and 
it appears to be convenient for the preparation of the monohydrated acid on 
a large scale. Melsens observed that when acetate of potash is supersatu¬ 
rated with acetic acid of moderate dilution, and evaporation allowed to take 
place, an acid-salt was the result, and that this on cooling became solid and 
crystalline; at a temperature of 248°P. in vacuo this salt does not part with 
its acid ; at 300° it begins to boil, evolving vapours of crystalline acetic acid, 
and at 572° neutral acetate of potash remains in the retort, being decom¬ 
posed on raising the temperature. This neutral salt combines with fresh 
dilute acid; the salt fixes a part of the acid, whilst another portion more 
dilute passes over in distillation. As the acid increases in concentration, a 
point is attained when the distilling product solidifies, but the temperature 
should be kept low. 
Whatever circumstances may have appeared to justify the estimation of 
the strength of acetic acid from its specific gravity, it is most fallacious,—a 
mere waste of time to adopt it. No reliable determination is given by such 
a mode, and it was long ago observed that the density of mixtures of the 
strongest acetic acid and water were, at a certain point, greater than that of 
the acid itself, and even in the commercial acid Mr. O’Neil observed that 
one sample, marking 6 of Twaddell, corresponding to specific gravity T030, and 
which should contain 22 per cent of real acid, was as good as another sample 
marked 9 of Twaddell, corresponding to specific gravity 1*049, and which 
should contain 38 per cent, of real acid,—both these samples being free from 
impurity. In other cases Mr. O’Neil observed that the contrary was the case. 
So anomalous is the state of matters with regard to this acid, that no ap¬ 
proach can even be made to correctness by taking the specific gravity of the 
stronger acid ; for whilst the specific gravity of the monohydrated acid is re¬ 
garded as about 1*063, and should contain 100 per cent, of aqueous acid, the 
same acid may be diluted with five atoms of water, or 51| per cent., and yet 
possess the same specific gravity of 1*063. Thus an acid containing one atom 
of water has a like specific gravity with one containing six atoms of water. 
Dr. Ure pointed out that a curious analogy exists in this respect with nitric 
acid, which suffers the greatest degree of condensation when one atom of the 
real acid is diluted with seven atoms of water. 
The following Table exhibits some of the relations of specific gravity to 
strength of acetic acid :— 
O 
An acid 
77 
77 
77 
77 
77 
77 
containing 100 per cent, monohydrated acid is 
of 
sp. gr. 1*063. 
77 
05 
79 
77 
' 77 
77 
1-070. 
77 
00 
77 
77 
77 
77 
1*073. 
77 
85 
77 
77 
77 
77 
1-073. 
77 
80 
77 
77 
77 
77 
1-073. 
77 
75 
77 
77 
77 
77 
1-072. ' 
77 
70 
77 
77 
77 
77 
1-070. 
77 
05 
77 
77 
77 
77 
1*068. 
77 
