PHARMACEUTIC METHODS 15 



to retain it. A 'percolator is a vessel with a porous diaphragm he- 

 low, into which the drug, in the form of a powder, is introduced 

 and Its soluble portions extracted by the descent of the solvent 

 through it. The menstruum or solvent is the liquid poured on top 

 of the powder. The liquid coming from the percolator, impregnated 

 with the soluble constituents of the drug, is the percolate. 



The first portion of the percolate is always more dense, more 

 highly colored and contains the largest proportion of the soluble 

 principles, because the first proportion of the menstruum, in its de- 

 scent through the powder, has the first opportunity to come in contact 

 with the largest proportion of the soluble principles which are to be 

 found in the finer dust scattered through the powder, and in the 

 thoroughly disintegrated particles, which offer but slight resistance 

 to the passage of the menstruum. When successfully conducted, 

 the first portion of the percolate will be nearly saturated with the 

 soluble constituents of the substance treated; if the quantity of 

 the menstruum be sufficient for its exhaustion, the last portion of 

 the percolate will be destitute of color, odor and taste, other than 

 that possessed by the menstruum itself. 



The general rule in percolation is to moisten the powder. The 

 reason for this is that most drugs are vegetable substances which 

 in their natural state were moist. The process of desiccation has 

 hardened and dried the tissues, so that they do not absorb mois- 

 ture quickly, and when compressed, as they are when packed in a 

 percolator, the resistance is still greater. If a dry powder is tightly 

 packed in a glass percolator and water poured upon it, the water 

 will penetrate the powder but a short distance. Its further passage 

 is prevented by the particles which are immediately in contact with 

 the water, which have become swollen to such a degree that they 

 press tightly against the sides of the percolator, and thus entirely 

 overcome the gravitating force and penetrating power of the 

 water. If, on the other hand, the powder is moistened with suffi- 

 cient water to satisfy its tendency to swell, hefore it is pacJced in 

 the percolator, the addition of water is followed by its slow eolation 

 through the mass without stoppage. A moist powder, like a moist 

 sponge, greedily absorbs moisture, but a dry powder, like a dry 

 sponge, repels attempts to moisten it. 



Care should be used in preparing and packing a percolator, 

 because upon this process largely depends the success of the opera- 

 tion. The powder should be packed firmly or moderately as directed. 

 If packed too firmly the menstruum will not pass through readily, 

 if not packed firmly enough the menstruum will pass through too 

 quickly and the full strength of the drug will not be obtained ;_ if 

 packed unevenly, the menstruum will pass readily through one side 

 of the mass and not come in contact with the other at all. The 

 menstruum should descend uniformly and slowly through the drug. 



