i May 6,1871.] 
THE PHARMACEUTICAL JOURNAL AND TRANSACTIONS. 
881 
PARCHMENT PAPER AS A FILTERING 
MEDIUM. 
BY CHARLES R. C. TICHBORNE, F.C.S., ETC. 
Tke Bunsen filter is now well known and familiar 
to most manipulators. It merely consists of a funnel 
and filter connected with an air-tiglit vessel, in the 
interior of which a partial vacuum can be produced, 
either by a Sprengel or ordinary air pump; in fact, 
by any contrivance by which a downward pressure 
of some considerable power is exerted upon the fluid 
washing some precipitate, or upon a liquid it is 
desirable to filter quickly. 
To give us the opportunity of doing this properly, 
it is necessary to have a nicely prepared support 
beneath the nozzle of the filter, to enable it to bear 
the considerable pressure to which it is exposed; 
the nozzle of the filter being the point of weakness. 
This is generally done by very carefully forming a 
little cone of platinum foil, which must exactly fit 
the bend of the funnel. If the fit is not perfect, it 
generally results in the breaking of the filter and 
the failure of the experiment. This is at once ob¬ 
viated, and the platinum nozzle dispensed with, by 
using parchment paper as a filter. Parchment paper 
bears, under such circumstances, any reasonable 
pressure; and yet it is a perfect filtering medium. 
As regards the strength, Dr. Hofmann sa} r s that it 
becomes five times as strong as the paper before it 
is parclimentized; and I think that, when speaking 
of moist bibulous paper, it is no exaggeration to say 
its strength is increased at least twenty times. 
In making the parchment paper for this purpose, 
the following method should be adopted. It differs 
very little from the ordinary one, except as regards a 
few precautions :—I use one part of pure sulphuric 
acid and one-half part of distilled water well mixed 
in a dish or shallow vessel. Where practical, this 
mixture should be ice cold, and under no circum¬ 
stances must it be used while it is warm. Pieces of 
Swedish filtering-paper should then be dexterously 
floated upon the acid, so as to bring every particle of 
the surface in contact with it. But it is not neces¬ 
sary to parclimentize both sides. The next point of 
importance after the cooling of the acid mixture is 
the quickness used in the washing, which must be 
thorough. 
This paper, which has proved itself so useful to 
us for dialytic purposes, forms the most perfect fil¬ 
tering medium, if properly managed, with which I 
am acquainted. Although, under ordinary circum¬ 
stances, it is nearly impervious to fluids, they pass 
through with perfect facility under pressure. The 
structural change produced by sulphuric acid upon 
cellulose is the converse of most of the other acids. 
Thus in paper converted into pyroxylene by the 
action of nitric acid the fibres are seen, when ex¬ 
amined with the microscope, to be more or less con¬ 
tracted, and the result is a non-contiguous, or friable 
structure, covered with small holes; but in parch- 
mentized paper the fibres are swelled considerably 
in bulk, and are converted into a colloid or gelati¬ 
nous substance, which, although slowly pervious to 
fluids, is very homogeneous in texture, and hence its 
strength. 
In Bunsen’s original paper he speaks of the diffi¬ 
culty of preventing filaments of the paper used from 
becoming mixed with precipitates. “ Thus,” he says, 
“ another and an inestimable advantage springs 
from the peculiar condition of a precipitate filtered 
Third Series, No. 45. 
by this method,—the surface of the filter becomes in¬ 
jured and torn, so that the precipitates become mixed 
with filaments of paper. Gelatinous precipitates 
(when washed under pressure) adhere to the filter 
in a thin coherent layer, and may be removed piece 
after piece so completely that the paper remains 
perfectly clean and white.” Now parchment paper 
is of that nature that it might be scraped with a 
knife or brushed, without invalidating a quantitative 
analysis. 
Parchment paper would be perfection for filtering 
by pressure ; but, alas! it has one drawback. The 
practical difficulty is in making the filter lie close to 
the funnel, so as not to permit atmospheric air to 
pass down by the side, instead of exerting its pres¬ 
sure upon the surface of the liquid in the filter. 
This difficulty is removed by placing an inner filter 
of ordinary filtering-paper larger than the parch¬ 
ment-paper one ; therefore, the latter should be thin, 
and only treated with acid on one side. It is from 
this reason that parchment paper may be used more 
advantageously in a Bunsen filtering-apparatus made 
on the principle of a percolator—the bottoms of the 
upper vessel being covered with good strong paper, 
strengthened with muslin; such an apparatus as 
this is applicable to many purposes, such as quick 
and thorough exhaustion of a powder by any men¬ 
struum, or the separation of crystals from a viscid 
liquid. 
BRISTOL PHARMACOLOGY. 
BY W. W. STODDART, F.C.S., F.G.S. 
(Continued from page 843.) 
Nat. Ord. Valeri an Acer. 
This is another very singular Order of plants, 
most of them having an extremely powerful odour, 
which is due to an extraordinary series of chemical 
products. 
Valeriana officinalis (Linn.). 
This attractive plant is found growing in moist 
places. It is found in the Leigh Woods, Lock’s 
Mills, Bedminster, Baptist Mills and on the banks 
of the Avon. The pink flowers are very conspicuous 
among the grasses and sedges of the water’s edge. 
The leaves are used by the country people, under the 
name of Allheal, as a cooling application to whitlows 
and boils. 
The roots (or rather rhizomes, from which spring 
fibrous roots) are a yellowish-wliite, becoming brown 
when dry. They contain 0 per cent, of resin and 
per cent, of a volatile oil. 
The essential oil of valerian is yellowish-green, 
having a strong odour of the plant, an acid reaction 
and a sp. gr. 0 0. It consists of 70 per cent, of 
valerol (C 6 H 10 O), which is a crystalline principle, 
easily changing into valerianic acid by the absorp¬ 
tion of oxygen. The other constituent is borneine 
(C 10 H 16 ) a liquid hydrocarbon isomeric with oil of 
turpentine. The valerianic acid (C 5 H 10 O 2 ) is, how¬ 
ever, the most important to the chemist. 
It is a colourless, oily liquid, and was first dis¬ 
covered by Chevreul in the fat of the dolphin. It 
occurs in the berries of Viburnum Opulus, and is pro¬ 
duced whenever fatty matters undergo oxidation, or 
albuminous substances putrefy, so that it is frequently 
present in animal secretions. 
