Glucosides, (the important pharmacopoeial examples are, Digitalin, 

 Salicin, Santonin) active principles which may be readily broken up by 

 acids or alkalies in the presence of water setting free glucose. 



Alkaloids, (e.g. Morphine and Strychnine) nitrogenous organic bases 

 usually pyridine derivatives which are generally crystalline though some 

 are liquid. They are usually sparingly soluble in water, but readily in 

 alcohol, chloroform, benzene, and ether. Like alkalies they form salts 

 with acids. Those with inorganic acids are usually soluble in water, 

 those with organic acids much less so. 



Tannins or Tannic Acids, These are weak acids containing a benzene 

 ring, astringent in taste, freely soluble in alcohol and water. They occur 

 very commonly in barks and roots and hence in pharmaceutical prepara- 

 tions of these they give precipitates with iron salts and some alkaloids. 

 Their presence must be remembered when such preparations are prescribed. 



In the following paragraphs the methods of preparation employed in 

 galenical pharmacy are denned. 



Solution, the physico-chemical process by which a solid or fluid (the 

 solute) disappears in a liquid (the solvent). The solute can usually be 

 re-obtained chemically unchanged by any process which will remove the 

 solvent. 



There are a few solutions in the pharmacopoeia in which a solid under- 

 goes a chemical change by the action of the solvent during the process of 

 solution, e.g. iron wire is dissolved in dilute acid to produce the Solution of 

 the Perchloride of Iron. 



Extraction, the process by which a solvent (or menstruum) removes 

 from a drug one or more of its soluble constituents. Four types of ex- 

 traction are made use of by the pharmacist. 



(i) Infusion In this process a suitably finally divided drug is treated 

 with either hot or cold water for a certain length of time, after which the 

 fluid portion is strained off and retained and the solid portion rejected. 



(ii) Decoction. In this process the active principle is extracted by boiling 

 in water. 



(iii) Maceration. In this process the drug is placed in a vessel, the sol- 

 vent poured upon it, and left to stand for a suitable length of time with 

 occasional agitation. The fluid is then filtered off; the marc or solid por- 

 tion pressed out, the fluid thus obtained being added to the filtrate and 

 the marc rejected. 



(iv) Percolation. In this process the drug is packed in a conical vessel 

 (a percolator) with a small outlet at its lower end and moistened with the 

 solvent which is added from time to time, and allowed to run off slowly 

 from the lower outlet until a certain quantity of solvent has passed through. 

 The marc is usually pressed out and the fluid obtained added to the per- 

 colate. 



Expression. In this process the drug is subjected to pressure and thus 

 its juices are obtained. 



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