PHARMACY. 



Such are the directions given in most 

 of Dr. Duncan's editions of the New 

 Edinburgh Dispensatory, for the depura- 

 tion of the decoctions, and we have in- 

 serted them at fall length, because, al- 

 though we doubt very much cf their 

 propriety, our reasons for so doing- are 

 scarcely more than hypothetical. We 

 would advise the decoctions to be evapo- 

 rated after they have been filtered boil- 

 ing hot, without any further depuration ; 

 because some of the most active princi- 

 ples of vegetable substances, such as tan- 

 nin, are much more soluble in boiling 1 than 

 in cold water, and because almost all of 

 them are very quickly affected by expo- 

 sure to the atmosphere. Therefore, if a 

 boiling 1 decoction, saturated with tannin, 

 be allowed to cool, the greatest part of 

 the very principle on which the activity 

 of the substance depends will separate to 

 the bottom, and according to the above 

 directions, will be thrown away as sedi- 

 ment. The same objection applies more 

 strongly to allowing the decoction to 

 cool, and deposit a fresh sediment, after 

 it has been partially evapoi-ated. Besides, 

 by allowing the d'ecoctions to stand se- 

 veral days before we proceed to their 

 evaporation, we are in fact allowing the 

 active principles contained in the decoc- 

 tion to be altered by the action of the 

 air, and to be converted into substances, 

 perhaps inactive, which also are thrown 

 uway as sediment. 



The evaporation is most conveniently 

 performed in broad shallow vessels : the 

 larger the surface of the liquor, the 

 sooner will the aqueous parts exhale. 

 This effect may likewise be promoted by 

 agitation. 



When the matter begins to grow thick, 

 great care is necessary to prevent its 

 burning 1 . This accident, almost unavoida- 

 ble if the quantity be large, ami the fire 

 applied as usual under the evaporating 

 pan, may be effectually prevented, by 

 carrying on the inspissation, after the com- 

 mon manner, no further than the consist- 

 ence of a syrup, when the matter is to 

 be poured into shallow tin or earthen 

 pans, and placed in an oven, with its 

 door open, moderately heated ; which 

 acting uniformly on every part of the li- 

 quid, will soon reduce it to any degree 

 of consistence required. This may like- 

 wise be clone, and more securely, by set- 

 ting the evaporating vessel in boiling- wa- 

 ter : but the evaporation is in this way 

 very tedious. 



Alcohol is much too expensive to be 



employed as a menstruum for obtaining 

 extracts, except in those cases where wa- 

 ter is totally inadequate to the purpose. 

 The cases are, 1. When the nature of the 

 extract is very perishable when dissolved 

 in water, so that it is liable to be decom- 

 posed before the evaporation can be com- 

 pleted, especially if we cannot proceed 

 immediately to the evaporation. 2. When 

 water is totally incapable of dissolving the 

 substance to be extracted ; and, 3. When 

 the substance extracted can bear the heat 

 of boiling alcohol without being evapo- 

 rated, but would be dissipated by that of 

 boiling water ; that is, when it requires a 

 heat greater than 176, and less than 

 212, for its vaporization. 



In the last case, the alcohol must be 

 perfectly free from water, because the 

 heat necessary to evaporate it at the end 

 of the process would frustrate the whole 

 operation. Hence, also, the subject itself 

 ought always to be dry: those substances 

 which lose their virtue by drying, lose it 

 equally on being submitted to this treat- 

 ment with the purest alcohol. 



In this way the alcoholic extract of 

 some aromatic substances, as cinnamon, 

 lavender, rosemary, retain a considerable 

 degree of their fine flavour. In the se- 

 cond case, the alcohol need not be so 

 very strong, because it is still capable of 

 dissolving resinous substances, although 

 diluted with a considerable proportion of 

 water. In the first case, the alcohol may 

 be still much weaker: or rather, the ad- 

 dition of a small proportion of alcohol to 

 water will be sufficient to retard or pre- 

 vent the decomposition of the decoction. 



The alcohol employed in all these cases 

 should be perfectly free from any un- 

 pleasant flavour, lest it be communicated 

 to the extract. 



The inspissation should be performed 

 from the beginning, in the gentle heat of 

 a water-bath. We need not suffer the 

 alcohol to evaporate in the air: the 

 greatest part of it may be recovered by 

 collecting the vapour in common distil- 

 ling vessels. If the distilled spirit be 

 found to have brought over any flavour 

 from the subject, it may be advan- 

 tageously reserved for the same purpose 

 again. 



When diluted alcohol is employed, the 

 distillation should only be continued as 

 long as alcohol comes over ; and the eva- 

 poration should be finished in wide open 

 vessels. 



Pure resins are prepared by adding to 

 spiritous tinctures of resinous vegetables 



