NO. III. PHARMACEUTICAL PREPARATIONS. 477 



The proportion of herbs or flowers required to afford a gallon of distilled 

 fluid will vary greatly according to the nature and qualities of the sub- 

 stance : of delicate flowers two-thh'ds the weight will be required, and 

 of strong aromatic herbs not more than one-eighth; and of aromatic 

 seeds about one-tenth. The plants to be distilled should be allowed to 

 macerate in the water for a few hours ; and some of the tougher vegetables 

 require a much longer time. Care should be taken that the water and 

 the ingredients do not occupy more than two-thirds of the still ; and the 

 fire should be quickly raised, and kept up during the whole operation. 



Distilled waters when recently prepared have a disagreeable empy- 

 reumatic odour, commonly called " smelling of the still" which they lose 

 by exposure to the air as long as any of the unpleasant odour remains ; 

 but they should immediately afterwards be put into glass vessels and 

 closely corked or stopped. 



After being long kept, many distilled waters become ropy and sour ; to 

 prevent which a little proof spirit is generally directed to be added to them, 

 but it is preferable to re-distil them, after which they will keep good for 

 several years. 



Common distilled water is sometimes required for pharmaceutical prepa- 

 rations. It may be obtained by means of the common still or by the more 

 simple method of having a pewter tube fitted to the spout of a common tea- 

 kettle, which may be kept cool, when in use, by being wrapped round with 

 wet rags. 



DISTILLED SPIRITS. 



The directions for distilling spirits are nearly the same as for the waters: 

 as much water must be put into the still as will prevent the vegetables from 

 burning, and the quantity of spirit intended to be drawn off should then be 

 added. The general proportion is a pound and a half of the vegetable sub- 

 stance to a gallon of spirit, drawing off a gallon. Proof or distilled spirit is 

 to be employed, because alcohol, in its rectified state, is more volatile than 

 many of the essential oils, which therefore do not rise with it in distillation. 



Mr. Waller observes, that those who wish to have their cordials very 

 agreeable to the taste, should use good French brandy ; it should only be 

 employed, however, when the plant to be distilled is not of a very volatile 

 nature. 



EXTRACTS. 



Extracts are formed by evaporating solutions of vegetable substances, 

 until a firm tenacious mass is obtained. They ought to contain all the 

 active principles of the vegetable from which they are prepared, but too 

 frequently the volatile matter is dissipated and the more fixed parts de- 

 composed by the process. An extract prepared from an infusion or decoc- 

 tion is termed an aqueous or watery extract; from a tincture, a spirituous 

 or alcoholic extract. When water is employed, the substance should be 

 coarsely powdered, or if tough, bruised. 



