Assuming now that we desire to transfer the dissolved matter equally to all portions of the liquid, we most easily accomplish the object by stirring the contents of the vessel until the menstruum above and the solution within are thoroughly incorporated. When allowed to rest, solution as before proceeds; and when we again stir the contents of the vessel, we transfer a certain proportion of dissolved matter to the overlying fluid. Each operation depletes the powder to an extent of soluble matters, and tends to produce an equilibrium between menstruum and material. The process of solution becomes gradually less active and at last ceases to any perceptible degree, at which point we find the liquid above the powder and the liquid within identical. However long we may allow them to remain together, and however violently they may be agitated, we cannot further deplete the powder without increase of temperature. This is maceration, and thus it is we cannot by maceration represent the powder operated upon, for when the supernatant liquid is filtered from the powder, soluble matters in proportion to the liquid within the powder must remain with it.
As the liquid obtained is to the entire menstruum, so must the material in the liquid obtained be to the material dissolved by the entire menstruum.
Other inconveniences attend the practical application of this mode of extracting the soluble substances from our plants. A very serious objection is the time required - generally 2 weeks. This, perhaps, more than any other cause, interested pharmacists in a general endeavour to improve. Another desideratum was an increase of strength in the product. We will consider briefly a slight modification of this process of maceration. Let us carefully moisten 2 oz. of powdered buchu with alcohol, press firmly into a container, and cover with the same menstruum. The operation of solution will be repeated exactly as in the other example. At length the liquid within the powder, and that in the cavities between its particles will be identical. When this state arrives, we remove the material to a press, and obtain all the liquid possible by pressure.
The residual material is again finely comminuted, macerated with fresh alcohol, and again submitted to pressure; the operation being repeated as many times as is considered necessary. It at first strikes us with reference to this process, that as we constantly remove saturated liquid from the powder, and substitute perfectly pure in its place, we must soon perfectly deplete the powder. But by any ordinary means we cannot remove all the liquid, and certainly that held within the powder must contain its full proportion of dissolved matters. Therefore, assuming that it required 4 oz. of alcohol, and the liquid within the powder and that between the particles had become identical in composition, and 3 oz. of liquid were obtained (a liberal allowance), 1/4 of the strength must remain in the residuum; consequently the 3 fl. oz. obtained containing 3/4 of the extractive matter represent 1 1/2 oz. of buchu, or 1/2 oz. of powder to each fl. oz., and each of the following operations dilutes this. At each successive step the powder, preceding and following maceration and expression, contains the same amount of liquid, and for every 4 oz. of alcohol applied, 4 oz. of solution are obtained, excepting loss by evaporation, which will not be considered here.
Decrease in quantity of powder by having a portion of its extractive matter removed by each maceration is also disregarded. The second expressed liquid we find represents but 4/5 of the extractive matters remaining in the powder, that is, 4/5 of 1/4, which is 1/5 of the whole, or original quantity, winch, added to the 3/4 obtained by the first operation, make the sum of 1/2 9/0 contained in 7 fl. oz. of solution, a little less than 3/20 to the fl. oz. The first operation produced 5/20 to the fl. oz., therefore there is a reduction of a little more than 3/20 to the fl. oz. by the second maceration. Theoretically this procedure may be carried to infinity before entirely exhausting the material. Practically the exhaustion will not be as thorough as our example represents. From considerations yet to be named, the writer believes it is impossible to obtain an expressed liquid containing substances of the plant capable of being dissolved by the menstruum, in the great proportion between successive percolates indicated by this ideal example. It is invariably found that a tenth maceration will produce an appreciable amount of extractive matter, and when we come to study the constituents of plants and their relations to menstruum, it will be doubtless accepted that such must be the case.
As the matter stands, those that favour this process cannot well object to the argument and table, inasmuch as it admits of the greatest possible depletion of the powder. Others may, perhaps, with good cause, argue that theoretical proportion of soluble matter extracted will be less than the above upon the assumption that the menstruum and the inert portion of the powder are alike impregnated with soluble matter, and that the actual proportion should be between menstruum squeezed from the mixture and entire residuum. Another trouble attending this process in practice is the necessity of finely dividing or pulverising each residue before rema-ceration, an operation tedious and difficult to accomplish in the majority of cases, especially when large amounts of material are worked. Lloyd never succeeded to his satisfaction in a general way, without passing the residuum through a sieve after each expression, an operation not easily accomplished, especially with substances which agglutinate, although in certain instances the process is preferable to any other. Our aim we understand to be the transference of soluble matter from material to liquid, if possible representing a grain of the material with a minim of the solution.
This latter result we have not yet accomplished, and cannot by either process of maceration examined. In the first case we operate directly against the laws of nature. We are continually transferring a dense solution upward. In the latter example we neglect to take advantage of nature's greatest force. We use manual labour to accomplish, in the way of separating the liquid, what gravitation will do for us to any extent, and better in every particular. Now let us modify the operation by repeating the experiment of maceration exactly as heretofore, but in a vessel with a layer of cotton at the bottom, and an exit below, care being taken to avoid stirring the powder. After the usual maceration, cautiously open the exit and allow the liquid to escape at the very bottom of the powder. As a consequence we obtain the densest liquid at first, and substitute in its stead at the surface perfectly fresh menstruum, with the advantage that the liquid extracted has always passed through the entire material. Thus we find the product is constantly decreasing in colour and flavour, and the powder is continually submitted to the action of a moving menstruum.