212 
BIIITISH PHARMACEUTICAL CONFERENCE. 
however, it has only been thought worthy of acting as a solvent for the tannin 
in “ Suppositoria Tannici.” The test there given is that it shall have a density 
of 1*26 (the new Pharmacopoeia of the United States gives D25). Price’s is 
almost the only sample I have met with which reaches this standard, the speci¬ 
mens of foreign glycerines I have examined being considerably below the mark, 
and, with one exception, having a disagreeable odour. This odour may easily 
be detected by rubbing a few drops on the back of the hand. One of the worst 
of these importations was advertised as “ equal to Price’s in every respect.” I 
have not detected much inorganic impurities in the foreign glycerines, and the 
presence of water would be of comparatively little import, if it were possible to 
free them from the well-known rancid odour, which renders them totally unfit 
for pharmaceutical uses. The olfactory nerves of that man must indeed be 
torpid, who fails to discover a wide difference between Price’s and the cheaper 
glycerines. Should odour, however, not be sufficient proof, let a little solution 
of nitrate of silver be added to the specimen in a test tube and exposed to the 
light; Price’s will be found to remain nearly colourless, whilst the inferior sam¬ 
ples will rapidly become dark-coloured. When we are able to obtain Price’s* 
glycerine, or glycerine equal to it in every respect, at Is. Gd. per pound, I have 
no doubt but it will find many applications in pharmacy from which it is now 
debarred by its great cost. • 
338, Oxf 07'cl Street , London. 
ON THE APPLICATION OF DIALYSIS IN DETERMINING 
THE NATURE OF THE CRYSTALLINE CONSTITUENTS OF 
PLANTS. 
BY J. ATTFIELD, PH.D., F.C.S., 
DIRECTOR OF THE LABORATORIES OF THE PHARMACEUTICAL SOCIETY OF GREAT BRITAIN. 
(Lead at the Bath Meeting of the British Pharmaceutical Conference , Sept. 1864.) 
Some two years ago (‘ Pharmaceutical Journal ’ for March, 1862) I published 
the results of an examination of the saline efflorescences which are occasionally 
found on medicinal vegetable extracts. These crystalline out-growths were found 
to be chloride of potassium or nitrate of potash. The former salt had often been 
observed, but the latter had not been noticed although it is of common occur¬ 
rence. From that examination, it seemed that nitrate of potash was a more fre¬ 
quent constituent of plants than had been suspected, and I then proposed the 
application of a method whereby the presence of it and of similar salts could be 
detected in the fresh plant. The suggestion was to dialyse expressed juices, con¬ 
centrated decoctions or infusions of plants, and then to evaporate the diffusate 
to a small bulk, when it was to be expected that the nitrate of potash, or any 
other crystalline salt would separate out in a solid and recognizable form. 
Since that time I have submitted a few plant-juices, the first that came to hand, 
to the process, and have obtained results which justify me in recommending the 
method as one likely to be of great service in the study of vegetable physiology. 
Crystalline salts can be thus obtained which would inevitably be destroyed in 
burning a plant for its ash. The following are the details of the experi¬ 
ments :— 
Solanum tuberosum .—A few pounds of potato tops were collected and at once 
crushed and pressed and the juice dialysed for twenty-four hours. On evapo¬ 
rating the diffusate and cooling, small prismatic crystals separated, having all 
the physical and chemical characteristics of nitrate of potash. Under the micro- 
f Mr. Wilson tells me that should the demand increase, the cost of Price’s glycerine 
will be greatly reduced. 
