478 APPENDIX. 



The following may be observed as a general rule for the preparation of 

 extracts : — The vegetable matter should be boiled in eight times its weight 

 of water down to one half; the liquor is then to be pressed out carefully 

 through cloth, and when the faeces have subsided, to be filtered without 

 being allowed to grow cold. The evaporation of the fluid is best performed 

 in a broad shallow vessel, for the broader the evaporating surface is, the 

 more quickly will the process be performed, and the quicker it is performed 

 the better. This, however, must by no means be done by increasing the 

 heat, for in no stage of the process must the temperature exceed that 

 of boiling water ; therefore it must be accomplished by means of a water 

 bath, that is, by placing the evaporating vessel in another containing boil- 

 ing water. This is a tedious process, but it is the only one that can 

 be depended on, as an increased heat would carry off all the active prin- 

 ciples of the plant. The process may be assisted by shaking the vessel, 

 and stirring up the fluid from time to time. When the matter begins to 

 thicken, great care is to be taken to prevent it from burning, and a con- 

 stant stirring with a wooden spoon becomes necessary to the end of the 

 process, which is when the matter acquires the consistence of thick honey. 

 The water used for the bath is best saturated with salt. 



The inspissated juices of plants are also called extracts, and are usually 

 prepared as follows : — The leaves are to be bruised in a marble mortar, 

 sprinkling a little water on them ; the juice is then to be expressed as it 

 is, without being cleansed, and evaporated as above to a proper consistence. 



The following method of preparing narcotic extracts is recommended by 

 Mr. Battley, (London Med. Repos. vol. iv.) " The fresh plants are to be 

 bruised and pressed, and the juice from them passed through a fine hair 

 sieve and immediately placed on the fire. Some time before it is raised to 

 the boiling temperature, a quantity of green-coloured matter begins to float 

 on the surface, which must be carefully removed as it rises by means of a 

 thin perforated tin dish, and preserved. The boiling is to be continued 

 until rather more than one half the fluid is evaporated, when the decoction 

 is to be put into a conical pan, and suffered to stand until cold. A large 

 precipitation of dark-green feculent matter will be discovered, from which 

 the supernatant fluid is to be poured off and again exposed to evaporation 

 until one half of it is consumed, when it is to stand for precipitation. The 

 remaining fluid is now to be suffered to boil till it acquires the consistence of 

 syrup, when the matter which had been collected at the commencement by 

 filtration and precipitation is to be mixed with it, and placed in a metallic 

 pan in a water bath, and further evaporated till of the consistence of an 

 extract. The operator must now give his constant attention ; and although 

 it is not necessary that the matter should be constantly stirred, it should 

 never be suffered to stick or become hard on the sides of the pan, as thereby 

 it loses its green colour and medicinal virtues." 



When alcohol is employed in the preparation of extracts, a tincture of the 

 substance is first obtained, and the evaporation is usually conducted in a 

 still, which should be heated by steam, and the spirit thus drawn off; the 

 process may then be finished as directed for aqueous extracts. 



