April 6,1872.] 
THE PHARMACEUTICAL JOURNAL AND TRANSACTIONS. 
801 
THE INTRODUCTION OF THE METRICAL 
SYSTEM OF WEIGHTS AND MEASURES 
INTO THE PHARMACOPOEIA.* 
BY C. H. WOOD, F.C.S. 
Since the publication of the present British Phar¬ 
macopoeia, two papers have been brought before this 
society by Professor Redwood, pointing out the de¬ 
sirability of promoting and facilitating the substitu¬ 
tion of the metrical system of weights and measures 
for those at present employed in English pharmacy. 
The arguments in favour of such a change are so 
numerous and powerful that it is unnecessary to 
urge them further. In the discussions which 
followed the reading of those papers, the advantages 
which would result from the introduction of the 
metrical system were generally appreciated and 
admitted. The practical difficulties, however, attend¬ 
ing a transition of this kind are very considerable ; 
and it is obvious that so important an alteration can 
only be brought about by very gradual means. 
It is in the Pharmacopoeia! processes that the 
practical defects of the present weights and measures 
are most apparent, and it is through the medium of 
the national Pharmacopoeia that the first steps 
towards the initiation of a more perfect system 
should be taken. 
But in dealing with authoritative formulae which 
so intimately concern the every-day detail of all 
pharmaceutical work, it is of great importance that 
nothing should be done which might occasion imme¬ 
diate inconvenience to those who have been long 
accustomed to the existing state of things, and who 
are unprepared for any material change. To afford 
facilities for the use of the metrical system in phar¬ 
macopoeia! processes by those who recognize its 
advantages, without interposing any obstacle to the 
employment by others of the weights and measures 
to which long usage has accustomed them, is the 
utmost which it would be wise to attempt in the first 
instance. It was avowedly considerations of this 
nature which induced Professor Redwood in his last 
paper to advocate the use of proportional numbers, 
instead of specified weights .and measures, for the 
description of processes in the next edition of the 
Pharmacopoeia. 
To express only the proportional relation of the 
ingredients to each other, admits of the employment 
of any system of weights, or the preparation of any 
quantity of product, at the option of each individual, 
and is, therefore, in many cases the most convenient 
method of arranging a formula. It applies most 
unexceptionably in the case of those preparations, 
the ingredients for which are taken entirely by 
weight, or entirely by measure. The Pharmaco¬ 
poeia includes a number of such formulae ; and if the 
Continental system of weighing liquids as well as 
solids prevailed in this country, no difficulty would 
be experienced in at once treating the entire work 
upon this principle. But Professor Redwood has 
very clearly shown that it is also quite possible to 
express, in proportional numbers, formulae involving 
both weighing and measuring, by simply indicating 
the fluids in parts by volume, or some word possess¬ 
ing that special meaning. This method of descrip¬ 
tion might be applied with the utmost ease to the 
* Read at the Evening Meeting of the Pharmaceutical 
Society of Great Britain, April 3, 1872. 
Third Series, No. 93. 
larger number of pharmacopoeial preparations, and 
no inconvenience or misapprehension could result. 
Most of the simple tinctures, for example, are in the 
proportion of 2| ounces to a pint, or 1 to 8, and a 
formula ordering 1 part of a drug to 8 fluid parts of 
menstruum, could equally well be rendered into 
ounces and fluid ounces, or grammes and cubic cen¬ 
timetres. It is evident, therefore, that the use of 
proportional numbers in all such cases would per¬ 
fectly answer the purpose of affording every facility 
for the metrical system without opposing any diffi¬ 
culty to those who prefer the existing weights and 
measures. 
But there are a considerable number of processes 
in the Pharmacopeia in which the quantities of in¬ 
gredients do not bear any simple numerical relation 
to each other; and it would be necessary to make 
some alteration in these before they could be ex¬ 
pressed in whole proportional numbers. This results 
from the grain having no relationship to the ounce, 
the minim, and the fluid drachm. Thus the present 
process for compound infusion of gentian, if described 
in parts, would require the use of fractions, unless 
the quantities of gentian and orange-peel were some¬ 
what reduced. In short, almost all those prepara¬ 
tions where the grain occurs are in the same position; 
the ingredients cannot be represented in any simple 
proportions without alteration. But if these prepa¬ 
rations are altered so as to represent the relative 
proportions of the constituents by whole numbers, 
another difficulty arises, namely, that it is no longer 
so easy to apply the existing weights and measures 
to the resulting formulae without somewhat intricate 
and troublesome calculations. 
Now it would be unadvisable to throw upon the 
pharmaceutist the labour of making such calcula¬ 
tions, with the attendant risk of error, whenever he 
requires to resort to these processes. In all those 
cases, therefore, where the use of the grain becomes 
necessary, I would suggest that the quantities of in¬ 
gredients, in the terms of our weight and measure, 
should be given in the Pharmacopoeia side by side 
with the proportional numbers. The adoption of 
tliis course would obviate the necessity for requiring 
pharmaceutists to provide themselves with large mea¬ 
sure-glasses graduated to grains instead of ounces, 
as proposed in Dr. Redwood’s paper. It would 
leave those who prefer it free to make all the prepa¬ 
rations of the pharmacopoeia with the same weights 
and measures which they have been hitherto using, 
while it would not interfere with any modification of 
the existing proportions which may be found neces¬ 
sary. 
Wherever such an alteration of the present quan¬ 
tities must be effected, it would be very desirable, as 
far as possible, to make the change in the direction 
of decimal or centesimal proportions, in order to de- 
velope to the fullest practicable extent the simplicity 
of the metrical system. Dr. Redwood has already 
proposed to convert a number of the liquors, which 
at present have a strength of 4 grains per fluid 
ounce, into one per cent, solutions. Such an altera¬ 
tion of strength would be so slight as to cause no 
practical inconvenience in the use of these prepara¬ 
tions, while it would greatly simplify the numerical 
relation of the ingredients. 
Of these liquors, three of them are simply' aqueous 
solutions of salts ; namely, Liquor Atropiie Sulplia- 
tis, Liquid Sodae Arseniatis, and Liquor Potassae 
Permanganatis. The two first would be written, 
