May 13,1S71.] 
THE PHARMACEUTICAL JOURNAL AND TRANSACTIONS. 
905 
indefinite!} 7 , and can be added to any desired vehicle 
at the time of taking; and ice-water appears to be 
about as good a vehicle for this, as for all saline 
substances, as any yet devised. When given to 
patients who have been long fasting it is often found 
to disagree with them, or at best to affect them less 
favourably than when given near a meal, or when 
the gastric secretions are not in the condition of long 
fasting. Hence, the syrup of orange-peel, or the 
mucilage, etc., with which it is common to give it, 
may not be without useful effect, and those physicians 
who have now abandoned these mixtures for the 
simple solution, often if not generally, advise their 
patients to eat a cracker, or take some other light 
food in small quantity, before or immediately after 
a hypnotic dose. When the medicine affects per¬ 
sons unfavourably, it should always be examined for 
hydrochloric acid by smelling and tasting, and by 
litmus paper. Nitrate of silver is too sensitive a 
test, for if the solution have been some time made, 
and especially when water containing organic matter 
is used, a cloudiness may be produced with this test 
which it is quite safe to disregard.— Proc. Am. Ph. 
Association, 1870. 
FILTERING-PAPERS AND FILTERS, 
With General Remarks on the Important Branch of 
Practical Pharmacy in which they are employed. 
BY JOSEPH M. HIRSH, OE CHICAGO. 
Original suggestions are almost impossible upon this 
practical topic, which, for we know not how many cen¬ 
turies, has busied not only the master minds occupying 
themselves with the sacred healing art, but everybody 
almost in all vocations of life; and the excellent sug¬ 
gestions regarding filters, laid down in all works on 
practical pharmacy, will be a sufficient apology for con¬ 
fining the present essay to a few observations on the fil¬ 
tering-paper and filters in general use. The main object 
of filtration, with especial reference to pharmacy, being 
the separation of a clear liquid from a solid residue, we 
must demand as of prime importance of the filtering- 
medium, that it offers a dense, uniform, unbroken sur¬ 
face to the liquid passing through it, so that no solid 
particles may pass through the same, the complete sepa¬ 
ration of which from the liquid is aimed at. 
The most ordinary objects of filtration at the pharma¬ 
cist’s are the preparations of clear tinctures, and the 
restoration of such liquid preparations as have grown 
turbid or deposited a sediment by standing, respectively 
by decomposition ; these latter instances being, a pity to 
say, by no means exceptional. For this object paper is 
mainly employed as a cheap and convenient medium. 
The general characteristics of good filtering-paper, like 
complete dense felting, uniformity, poverty in soluble 
salts, constituting its ashes, are well known, and your 
reporter can only repeat the experience of many who 
have found good Swedish filtering-paper to fulfil all 
claims of prime quality made upon it. But it was always 
selected with some partiality, because upon repeated tests 
of the ordinary filtering-paper, obtainable in our back- 
woods town of Chicago, a sad deficiency was found. 
Three qualities were chiefly obtainable. 
The French grey filters, coming in round sheets, ready 
for folding; square grey sheets, sometimes of lighter 
colour and white; square sheets, so-called Swedish filter¬ 
ing-paper, which it might be, although the coolness with 
which it keeps its name is the only sign of its northern 
homb. It is not felted evenly, some spots being quite 
heavy, while others are so thin as to be semi-transparent, 
and others again permit not only the passage of light, 
but of solid tangible substance. In fact I could never 
obtain any Swedish filtering-paper here but what had 
at least some pinholes. Of the grey filtering-paper, the 
round French, as also the square, twenty sheets in each 
hundred examined contained pinholes. Such paper is 
perfectly useless for the separation of some precipitates, 
while it may answer for the separation of others, such as 
would fill up even the gigantic pores of imperfect filters. 
In this case the first turbid filtrate would have to be re¬ 
turned upon the filter, upon which the deposition of the 
first precipitate then forms the true filtering medium. 
The safest way in using such filtering-paper is to use 
a double filter, when the dense, unbroken sheet of the 
one, upon being moistened, will closely press against the 
sides of the second filter, thus closing up any imperfec¬ 
tions present in the same, although there is one much 
better way, namely, not to use such filtering-paper at all. 
In some cases the use of double or even quadruple filters 
becomes necessary, even if the quality of the paper is 
excellent, as in the filtration of concentrated aqueous 
solutions of oils or carbolic acid, when a clear solution is 
desired. In this case the benefit resulting from the use 
of several layers of paper is not only due to the greater 
depth of the filtering medium through which the liquid 
has to pass, but to the different direction given to the 
liquid dining its passage through each filter, so that it 
pursues a zigzag course through the different strata of 
paper, which is equivalent to a longer and more obstructed 
passage, with which the good effect of filtration increases. 
Paper filters, on account of the feeble strength of the 
material and its limited size, can only be used for opera¬ 
tions upon a small scale; and for such we often find a 
preferable substitute in clean, well-washed cotton batting, 
a small quantity of which is pressed into the neck of a 
common funnel, which then is filled with the liquid to 
be filtered. The cotton plug may be made as loose or 
firm as the filtering liquid demands; its dimensions, re¬ 
spectively to its depth, may also be increased or decreased 
at pleasure, liquids of great fluidity passing readily 
through a dense and deep cotton plug; while syrups 
filter only through a loose plug, unless pressure is ap¬ 
plied. For this purpose, also, cotton is preferable, as 
considerable pressure can be used to increase the speed 
of filtration; while paper would not be strong enough to 
resist that pressure without especial care and precaution, 
such as using at the same time a filter of cotton cloth, which 
sustains the pressure, and upon which the paper filter 
lies, so as to make no folds, while the funnel which sup¬ 
ports the filter must have exactly an angle of 45 degrees, 
so as to ensure the close adherence of the filter to the 
walls of the funnel. A small platinum cone may also be 
slipped over the joint of the filter, having the same angle, 
to add to its strength to sustain the pressure. The fur¬ 
ther construction of pressure-filters has been so fully a 
subject of discussion in the pharmaceutical press, that I 
may safely pass it by with the suggestion that the sim¬ 
plest pressure-filter is a siphon, where filtration would 
take place upward through the short arm of the same. 
To do this successfully, the opening of this short arm 
must be very wide, narrowing down funnel-like to the 
tube, which should be of very small calibre. The differ¬ 
ence in width between the short and the long arm must 
be very great, to render the siphon useful as a filter, for 
the reason that only a large opening closed by the ob¬ 
structing filtering medium will admit through the latter 
a sufficiently large amount of liquid to keep the long 
arm of the siphon-tube filled. Should less than that 
amount of liquid pass through, air will enter and will at 
once disturb the action of the siphon. 
On a large scale the pharmacist rarely has occasion to 
use filters except in percolation, which perhaps hardly 
belongs within the scope of this paper, since filtration 
has simply the object of separating a liquid substance 
from a solid one, while percolation proper, in the cus¬ 
tomary pharmaceutical sense of the term, by means Of 
filtration accomplishes also the extraction of soluble sub. 
