520 MATERIA MEDICA 



may be cases, however, in which the spirit may be improper, 

 and then the watery mixture should be preferred. Opium is 

 decomposed by ammonia, potash, and soda, and their sub-car- 

 bonates, morphia being precipitated : also, by most metallic salts 

 and infusion of galls : such combinations should therefore be 

 avoided ; but, in combination with vinegar, the vegetable acids, 

 and oil, its strength or narcotic power is said to be rather in- 

 creased, being thoroughly extracted. 



The mode of purifying opium, prescribed in the London Dis- 

 pensatory, is to dissolve it in proof spirit, then filter the solu- 

 tion, and evaporate in a water bath to the required consistence ; 

 but a more ready way, though not so effectual, is to dry it care- 

 fully by a moderate heat, powder, and sift it. The sieve will 

 keep back many of the impurities, when this is carefully done. 

 Opium is an article of so much importance, that it appeared 

 necessary to notice it particularly, and at some length. There 

 is a vinous tincture of opium sometimes used in diseases of the 

 human eye. I have found it very useful in chronic inflamma- 

 tion of the horse's eye, applied undiluted. If, however, ten 

 parts of distilled water be added to six parts of tincture of 

 opium, the strength of wine of opium will be obtained, and the 

 mixture will be applicable for the same purposes in the horse. 



[Opium contains two peculiar vegetable compounds, in which 

 its power resides ; one of these is an alkaline substance, called 

 morphia ; the other does not possess similar chemical properties, 

 and has received the name of narcotine. Morphia exists in 

 opium, in combination with a peculiar acid, called the meconic 

 acid ; and the salt is termed meconate of morphia. The acid 

 has no narcotic power. 



Morphia may also be obtained by adding a solution of am- 

 monia to one of opium in acetic acid ; the acetate of morphia 

 formed is decomposed, and the morphia is immediately precipi- 

 tated of a brownish colour, which may be removed by boiling in 

 water with animal charcoal. 



Although it seems sufficiently proved that morphia possesses 

 the characteristic properties of opium, yet its strength is not 

 coramensui'ate with its apparent concentration ; and, when un- 

 combined, it exerts but Httle action, in consequence of its 

 insolubility. 



It is supposed that the excitement which opium produces is 

 owing to narcotine, and the subsequent sedative effect more 

 particularly to morphia. — Ed.] 



OPODELDOC. — Linimentum Saponis Compositum. This 

 is made by digesting three ounces of soap in a pint of spirit of 

 rosemary until it be dissolved, and then adding one ounce of 

 camphor. It is either liquid or solid. The former, when made 

 with soft soap ; the latter, when with hard soap. In the solid 



