4th. Tincture of kino changes so with time, that it passes from the liquid to the gelatinized state. This change even affords an excellent test when it is suspected that catechu may have been substituted for kino in this preparation.—(Dorvault, Officine, 1850, 3d. ed.)
In general, pharmacologists consider that tinctures only deteriorate by the evaporation of the alcohol used in their preparation, and that this evaporation has the effect of concentrating them too much, and of giving rise to the precipitation of a part of the principles which were held in solution.
I do not entirely concur in this opinion; on the contrary, I {203} believe that, in many cases, the precipitates which are formed in the tinctures, do not arise from the evaporation of a part of the vehicle, but from a modification which takes place in a part of the principles held in solution, and which, becoming less soluble, or even insoluble, are precipitated.
Amongst these precipitates I shall place that which is almost uniformly found in tincture of ipecacuanha.
Druggists generally are aware that this tincture, shortly after its preparation, throws down a deposite of a yellowish white color, very light, and increasing daily; that when separated by filtration a new deposit immediately commences, and recourse must again be had to filtering.
It is only after three or four filterings, at intervals of five or six weeks, that the formation of this deposit can be arrested. In the course of July of this year, I prepared from the Belgian Pharmacopœia, some tincture of ipecacuanha, to be used in the preparation of some syrup of the same.
Desiring to follow the different phases which it presents, and to study, as far as possible, the nature of the precipitate formed in it, (for as yet I believe that no research has been directed to this subject.) I took advantage of the opportunity which this preparation afforded me.
About six weeks after its preparation, this tincture contained a deposit which was yellowish white, tolerably abundant, very light, and rising on being shaken.
I again suffered the precipitate to form, and after some days, I decanted the clear liquor, and threw the deposit on a filter. I afterwards mixed the decanted liquors and that which was filtered, in a bottle.
The precipitate remaining on the filter, I repeatedly washed. I put it to dry spontaneously, but perceiving, after twenty-four hours, that it was becoming the prey of a number of little cryptogami, formed in the same manner as in animal gelatine which dries slowly in the air, I hastened the desication by carrying the filter into a medium of from 30° to 35° centigrade. {204}