ON THE PREPARATION OF TINCTURES. 
545 
had already been adverted to by Dr. Redwood, who bad gone so fully into 
the subject, as to leave him little* to say on the matter. His experience on 
this subject was somewhat large, having carefully practised it from the time 
be first brought it before the notice of the Society at one of its earliest 
meetings, held at the bouse of the late Jacob Bell. He commenced upon a 
plan recommended in the ‘ American Journal of Pharmacy ’ (vol. x. p. 1), and 
had not proceeded far before he found that there was much to learn before 
he could get at the secrets of the process. The condition and character of 
the dry materials, the amount of moisture to be employed, the packing in the 
cylinder, the rate of percolation, and the correct form of apparatus, had all to 
be studied. Perhaps the first difficulty was the packing in the cylinder; for if 
too tightly packed, the fluid would not pass through, and if too loosely, it would 
run too fast, involving the necessity for a large quantity of fluid to exhaust 
the substance. This led to the use cf a tap to regulate the flow, and which 
was of great assistance. Prom its use was learned the fact that the slower 
the operation, the smaller the quantity of fluid required to exhaust the material. 
This suggested what might be termed a fractional mode of displacement; 
that was, drawing off definite quantities at definite and regular intervals 
of time, and taking the specific gravity of each quantity drawn off. By 
this method the best rate of displacement was in time determined for each 
particular substance. Up to the present time, he had made between three 
thousand and four thousand weighings in a specific gravity bottle, and had 
learned much from it, especially this, that it is not a simple process of dis¬ 
placement or percolation, but both, combined with maceration; for instance, 
oil on the top of water in a cylinder will displace the water, but when a mul¬ 
titude of particles of matter are surrounded with a quantity of fluid denser 
than that which is intended to displace it, the superincumbent fluid does not 
so readily drive it forward as is apt to be imagined. Let this cylinder full of 
marbles represent the case. Every marble wetted with the denser fluid would, 
from the cohesive force exerted, allow the lighter fluid to pass without carrying 
all the soluble matter before it, and that in proportion to the velocity with 
which the liquid was run off; and if these particles represented by the marbles 
were particles of rhubarb, or any other cellular tissue, the cohesive force 
would be complicated with endosmotic and exosmotic action, involving the 
necessity for a considerable amount of maceration at the same time. Hence 
it was found that the interstitial fluid even could not be simply displaced, much 
less that which was intercellular, and the fluid passed away in a constantly de¬ 
creasing ratio of density, as shown in the following illustration :— 
Dry Material, 65 oz. troy weight. Wet with 106 fl. oz. of proof spirit, sp. gr. -923, mace¬ 
rate three days, pack tightly in a percolator, when it was found that a very small 
quantity (T oz.) would just drain from it. Percolate with proof spirit as above, to the 
extent of 16 pints = 320 fl. oz. 
1st 3 oz. had sp. gr. of. 080 
of 1st 40 oz. „ .976 
1st 3 oz. „ . 971-2 
of 2nd 40 oz. „ . 969 - 6 
1st 3 oz. „ . 962 
of 3rd 40 oz. „ . 957-6 
1st 3 oz. „ . 950 
of 4th 40 oz. „ .946 
1st 3 oz. „ . 940 
of 5th 40 oz. ,, . 937 - 2 
1st 3 oz. „ . 934-4 
of 6th 40 oz. „ . 932 - b 
1st 3 oz. „ . 929 6 
of 7th40oz. „ ’...... 930 
