474 
LECTURES ON THE BRITISH PHARMACOPOEIA. 
are conducted by some of our wholesale druggists, and especially whether, if 
applicable, it is necessary. The usual mode of making these extracts is to 
heat the juice to near its boiling-point, and separate the chlorophyll and albu¬ 
men, which at that temperature coagulate together; then to evaporate the 
strained liquor in a steam bath, and when reduced to a syrupy consistence to 
mix in the green colouring-matter, and bring the whole to a pilular consis¬ 
tence, finishing it off at a low temperature. As thus prepared, the extracts are 
not found to be deficient in the qualities that would characterize those 
made by the new process. The separation first of the chlorophyll, and 
afterwards of the albumen, by processes which require a nice regulation of 
temperature, may be thought to involve unnecessary trouble and loss of time 
in an operation in which expedition is of the greatest importance ; and this 
will especially be felt in operating upon the large scale, where a ton or 
two of fresh herb is collected in the morning, and has to be converted into 
extract before the day has passed. All unnecessary delay is here a source of 
deterioration in the product, and this applies also to the means by which the 
evaporation is to be effected. 
We are directed in the process, after separating the chlorophyll and albu¬ 
men, to evaporate the strained liquor to the consistence of a thin syrup by a 
water-bath. Now the question arises here, what is meant by a water-bath ? 
In former Pharmacopoeias terms of this sort have been explained, but in this 
Pharmacopoeia we have no such explanations, excepting with regard to weights 
and measures, and temperature. If we turn to the London Pharmacopoeia, 
we find that “ a water-bath is made when any substance contained in a proper 
vessel is exposed either to hot water or to the vapour of boiling water.” 
This, it is true, is a very imperfect explanation, for it does not indicate the 
temperature of the hot water or of the steam. But it makes the term appli¬ 
cable to a steam-bath as well as a water-bath, and as we are directed to make 
extracts in a water-bath, and in making them are told in parts of the pro¬ 
cesses to boil the liquor, it is obvious that the water or the steam used for 
this purpose must be hotter than 212°, for water at 212° applied to the out¬ 
side of the pan will never cause water inside the pan to boil. 
The usual practice now is to substitute steam-baths for water-baths; and 
this is a most important point in connection with the preparation of extracts, 
for while the process of evaporation may be thus greatly expedited, the 
difference between the rate of evaporation in a steam-bath, where the steam 
is under a pressure of from ten to twenty pounds to the inch, and a water- 
bath, where the temperature of the evaporating liquid never exceeds 200° 
Tahr., being about as two to one, the heat may at the same time be raised, 
and often is raised, to a point very injurious to the substances operated 
upon. This, however, forms part of the subject of evaporation which 
the time will not admit of my entering into, beyond referring you to 
the apparatus and arrangements for the preparation of extracts, by spon¬ 
taneous evaporation, by evaporation in vacuo, and by evaporation in tbe 
water or steam bath. These different forms of apparatus, which I have long 
been accustomed to use practically and for lecture illustration, are before 
you, but I must content myself with stating briefly, that as a Pharmacopoeia 
process, intended for the use of all classes of pharmaceutists, it would be use¬ 
less, or at least unwise, to order any complicated or expensive arrangements; 
and I think it has been rightly decided to direct these and similar operations 
to be effected by the use of the w r ater-bath, although at the same time I 
think it was a mistake to omit to indicate what the water-bath was intended 
to be, as the term is often used in an ambiguous sense. 
Before I leave the subject of extracts, a word or two must be said with 
reference to the new forms introduced among them for what are called liquid 
