ON THE PREP Alt ATION OF TINCTURES. 
537 
liand, there is a constant change of particles, caused by the manner in 
which the liquid is made to pass through the solid mass, from particle to 
particle, and from mass to mas3, so that the action is here much more com¬ 
plete and efficient than it is in the other case. 
But the process is not merely one of percolation, it is also a process of dis¬ 
placement, and much of its value depends upon the means it affords, after the 
soluble matter has been dissolved or extracted by percolation, of separating 
this from the solid mass. It may sometimes happen that all that is required 
to be separated from the solid substance can be dissolved by the quantity of 
liquid absorbed and retained by capillary attraction in the pores of the mass. 
In such a case, in operating by the process of maceration, we can only get at 
the product by expression, and as this effects the separation of only a part, the 
remainder of the concentrated and it may be valuable solution is lost; but in 
the process of percolation the product is separated by displacement, and by 
this means we obtain the whole or nearly the whole of it. The displacement 
is effected by continuing the percolation with fresh portions of the liquid after 
the quantity required for solution has been used. It rarely occurs, however, 
in cases such as I am contemplating, that complete exhaustion of everything 
soluble is effected within the limits of a practical operation. We do not find 
that the liquid first used dissolves all that is soluble, and that a further addi¬ 
tion of the same liquid displaces the first solution without becoming itself 
charged with any soluble matter. The first may contain the principal part 
of the soluble matter, and that which follows may have comparatively little, 
but there will be no well-defined line of demarcation between the solution 
and the liquid used for its displacement, the one will gradually merge by 
successive shading into the other, and there will not generally be an entire 
absence of soluble matter from the percolating liquid even to the last. In 
operations in which water, either cold or hot, is used as the solvent, and in 
which the product is afterwards concentrated by evaporation, the percolation 
may be continued until nothing more is extracted worth separating, and the 
liquor then remaining in the marc will be left as worthless. If spirit be used 
as the solvent, and the solution is not required to be produced in a concen¬ 
trated state and of definite strength, the percolation can be carried on, as in 
the previous case, until nothing more worth getting is extracted, and spirit 
alone will then be left in the marc; but in the preparation of tinctures the 
case is different, and here it is necessary to use a definite quantity of the 
solvent, and to limit the product without reference to the complete or incom¬ 
plete exhaustion of the substances operated upon. It is with reference to its 
application for the preparation of tinctures that I am now considering this 
process, and the most important object, next, or indeed equal, to that of getting 
a perfectly efficient preparation, is the production of definite results that shall 
not be liable to variation when obtained at different times and by different 
operators. 
It is not easy, even in this process, to avoid slight variations in the details 
which may affect the results. Thus, if there should be differences in the state 
of comminution of the solid substances, this would be a possible source of 
variation in the product; but even if the solid ingredients were always reduced 
to the same state of comminution, there may stiff be differences in the results, 
arising from the different amounts of pressure applied in packing or produced 
by the weight of the ingredients themselves according to the quantity con¬ 
tained in the percolator. 
But there is a source of variation in the products, as frequently obtained, of 
a far more serious character, arising from the use of water for displacing the 
tincture first formed with spirit. There is a strong inducement for the use of 
water as a displacing liquid to save the employment of spirit, for if the dis- 
