NOTES ON PRESCRIBING. 447 



a recent number of tlie Journal de Pharmacie et de Chimie. 1 M. 1867. 

 Melsens has proved by experiment that pure potassium iodide Unexpected 

 may be administered to dogs in considerable doses without oc- 

 casioning any ill effects ; and that potassium chlorate in some- 

 what strong doses is also tolerated when administered continuously 

 for at least a month. Treated with potassium iodate, however, 

 dogs die rapidly. If potassium iodide and potassium chlorate in 

 equivalent proportions are given to dogs, such mixture speedily 

 proves fatal ; and yet, as is well known, these salts do not 

 under ordinary circumstances decompose one another. These ex- 

 periments have an important practical bearing on the art of pre- 

 scribing, showing that medicines, harmless when administered 

 separately, may become highly deleterious when given in com- 

 bination. 



The following case of unexpected change in the composition Rochelle salt 

 of a medicine was of actual occurrence. A prescription was 

 written for a mixture of which the more essential ingredients 

 were rochelle salt and calcined magnesia, the one dissolved, 

 the other diffused in peppermint water. The mixture was pre- 

 scribed and taken without particular remark, until upon one 

 occasion, recourse was had to a bottle which had been prepared 

 some weeks before. The dose was found extremely different 

 from any that had been taken previously ; in fact it had so 

 caustic a taste as to excite the alarm of the patient who sus- 

 pected a serious error on the part of the druggist. The physician 

 was consulted, and finally an analytical chemist was requested 

 to examine and report on the medicine. This resulted in an ex- 

 planation : the calcined magnesia, by prolonged contact with 

 the alkaline tartrates, had gradually abstracted their tartaric acid 

 leaving their alkalies in a free and caustic state. 



The dispenser of prescriptions is sometimes puzzled to know Change of 

 what colour to make the medicinej the colour being dependent on colour * 

 the order in which the ingredients are mixed. For' instance, a 

 lotion was prescribed composed of calomel, lime water, and 

 chloride of zinc. If the calomel were decomposed first, the 

 lotion was Hack : if the chloride of zinc first, it was white. 

 1 November, 1866, page 338. 



