24 



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 menstrum 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 wliich 

 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 tight- 

 ly 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, before it is packed 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 absorbes 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. 



