552 
NOTES ON PRESCKIBING. 
In preparing this medicine, the iodide and bicarbonate were dissolved in a 
portion of the water, to which the tincture was then added. The citrate was 
dissolved in the remainder of the water and the two solutions were mixed. The 
result as might be expected, was that a frothy white precipitate of quina was 
instantly formed which in a few minutes collected into a coherent mass, suffi¬ 
ciently hard and tough to be rolled into pills. 
It may be observed that in compounds such as this, the quina is not subject 
to the remarkable influence which citric or tartaric acid exerts on peroxide of 
iron,—that of allowing it to be combined with an alkaline bicarbonate or with 
ammonia, but that it is more or less separated when such alkalies are mixed with 
it, a fact very often overlooked. 
A third instance of extremely unsuitable combination occurs to me, which 
from its frequency a few years ago was impressed on my memory, although I 
have no copy of a prescription in which it was ordered. It was the prescribing 
of glacial phosphoric acid in pills, and that in combination with valerianate of 
zinc! 
Formula that give rise to unexpected combinations. A very interesting fact 
bearing on this point has been stated in a recent number of the Journal de Phar- 
macie et de Chimie.^^ M. Melsens has proved by experiment that pure iodide of 
potassium may be administered to dogs in considerable doses without occasion¬ 
ing any ill effects; and that chlorate of potash in somewhat strong doses is also 
tolerated when administered continuously for at least a month. Treated with 
iodate of potash however, dogs die rapidly. If iodide of potassium and chlorate 
of potash in equivalent proportions are given to dogs, such mixture speedily proves 
fatal;—and yet, as is well known, these salts do not under ordinary circum¬ 
stances decompose one another. These experiments have an important prac¬ 
tical bearing on the art of prescribing, 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 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 prescribed 
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 suspected a serioits error 
on the part of the druggist. The physician was consulted, and finally an ana¬ 
lytical chemist was requested to examine and report on the medicine. I'his re¬ 
sulted in an explanation:—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 what colour to 
make a medicine, the colour being dependent on the order in which the ingre¬ 
dients 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 blade: if the chloride of zinc first, it was white. 
Lotions in which both chloride and bichloride of mercury are ordered with 
lime water, are easily made to vary from yellow to brown or black, according to 
the order in which the two mercurials are decomposed. A lotion made according 
to the following formula is either transparent and colourless, or opaque and of a 
brick red, according to the order in which the ingredients are mixed: 
^ I^ovembcr, 1863, page 328. 
