PHARMACY. 



in no reed of maceration, but are eveo in- 

 jured by it. The fermentation which was 

 formerly prescribed in some instances, is 

 always hurtful. 



With regard to the fire, the operator 

 ought to be expeditious in raising 1 it at 

 first, and to keep it up during the whole 

 process, to such a degree only, that the 

 oil may freely distil ; otherwise the oil 

 will be exposed to an unnecessary heat ; 

 a circumstance which ought as much as 

 possible to be avoided. Fire communi- 

 cates to all these oils a disagreeable im- 

 pregnation, as is evident from their being 

 much less grateful when newly distilled, 

 than after they have stood for some time 

 in a cool place : and the longer the heat 

 is continued, the greater alteration it pro- 

 duces in them. 



The greater number of oils require for 

 their distillation the heat of water strongly 

 boiling : but there are many also which 

 rise with a heat considerably less ; such 

 as those of lemon and citron peel ; of the 

 flowers of lavender and rosemary, and of 

 almost all the more odoriferous kinds of 

 flowers. We have already observed, that 

 these flowers have their fragrance much 

 injured, or even destroyed, by beating or 

 bruising them ; it is impaired also by the 

 immersion in water in the present pro- 

 cess, and the more so in proportion to the 

 continuance of the immersion and the 

 heat; hence oils, distilled in the common 

 manner, prove much less agreeable in 

 smell than the subjects themselves. For 

 the distillation of substances of this class, 

 another method has been contrived ; in- 

 stead of being immersed in water, they 

 are exposed only to its vapour. A pro- 

 per quantity of water being put into the 

 bottom of the still, the odoriferous herbs 

 or flowers are laid lightly in a basket, of 

 such a size that it may enter into the still, 

 and rest against its sides just above the 

 water. The head being then fitted on, 

 and the water made to boil, the steam, 

 percolating through the subject, imbibes 

 the oil, without impairing its fragrance, 

 and carries it over into the receiver. Oils 

 thus obtained, possess the odour of the 

 subject in an exquisite degree, and have 

 nothing of the disagreeable scent per- 

 ceivable in those distilled by boiling them 

 in water in the common manner. 



Plants differ so much, according to the 

 soil and season of which they are the pro- 

 duce, and likewise according to their own 

 ages, that it is impossible to fix the quan- 

 tity of water to be drawn from a certain 

 weight of them to any invariable stand- 

 ard. The distillation may always be con. 



tinned as long as the liquor runs well 

 flavoured oft i he subject, but no longer. 



In the distillation of essential oils, the 

 water, as was observed in the foregoing- 

 section, imbibes always a part of the oil. 

 'The distilled liquors here treated of, are 

 no other than water thus impregnated 

 with the essential oil of the subject ; 

 whatever smell, taste, or virtue, is com- 

 municated to the water, or obtained in 

 the form of watery liquor, being found in 

 a concentrated state in the oil. 



All those vegetables, therefore, which 

 contain an essential oil, will give over 

 some virtue to water by distillation : but 

 the degree of the impregnation of the 

 water, or the quantity of water which the 

 plant is capable of saturating with its vir- 

 tue, are by no means in proportion to 

 the quantity of its oil. The oil saturates 

 only the water that comes over at the 

 same time with it : if there be more oil 

 than is sufficient for this saturation, the 

 surplus separates, and concretes in its 

 proper form, not miscible with the water 

 that arises afterwards. Some odoriferous 

 flowers, whose oil is in so small quantity 

 that scarcely any visible mark of it ap- 

 pears, unless fifty or an hundred pounds 

 or more are distilled at once, give never- 

 theless as strong an impregnation to wa- 

 ter as those plants which abound most 

 with oil. 



Many^ have been of opinion, that dis- 

 tilled waters may be more and more im- 

 pregnated with the virtues of the subject, 

 and their strength increased to an)- as- 

 signed degree, by cohobation, that is, by 

 re-distilling them repeatedly from fresh 

 parcels of the plant ; experience, how- 

 ever, shews the contrary. A water, skil- 

 fully drawn in the first distillation, proves, 

 on every repeated one, not stronger, but 

 more disagreeable. Aqueous liquors are 

 not capable of imbibing above a certain 

 quantity of the volatile oil of vegetables ; 

 and this they maybe made to take up by 

 one, as well as by any number of distilla- 

 tions : the oftener the process is repeat- 

 ed, the ungrateful impression which they 

 generally receive from the fire, even 

 at the first time, becomes greater and 

 greater. 



Those plants which do not yield at first 

 waters sufficiently strong, are not proper 

 subjects for this process. 



The mixture of water and oil which 

 comes over, may either be separated im- 

 mediately, by means of a separatory, or 

 after it has been put into large narrow- 

 necked bottles, and placed in a cool place, 

 that the portion of oil which is not dis- 



