By R. ROTHER.
If the statement is correct in regard to the yield of cyanhydric acid from wild cherry bark, then the syrup of this drug must be a more potent preparation than is generally granted. It is alleged that the best wild cherry bark, gathered in October, produces .1436 per cent. of cyanhydric acid, and that in addition the bark contains at this period of the year the largest amount of tannin and peculiar bitter principle. The cyanhydric acid, or rather the constituents that produce it are by all means the most essential part of the drug. The bitterness and astringency are, however, also of sufficient importance to demand particular attention. With the stated amount of absolute acid in the bark the syrup would contain .1436 * 50 * .12 = .8616 per cent. of the official acid by weight, or somewhat over one per cent. by volume. This shows that an ordinary teaspoonful of such a preparation represents approximately one minim of official cyanhydric acid. With an appropriately fine powder, of the requisite quality, in a carefully conducted operation that standard could perhaps be uniformly attained. But owing to the fact that syrup of wild cherry is not usually conceded to be anything more than a mere adjuvant, its proper preparation is generally unduly neglected. Under this adverse condition it is probable that syrup of wild cherry is but feebly representative of its most powerful constituent. The keeping qualities of the syrup are ordinarily good during a moderate period of storage. But in the generality of cases, with longer time and frequent exposure deterioration and decomposition become so marked as to call, emphatically, for some preservative.
The decomposition is of several kinds. The first that appears results from the formation of mould over the surface, assuming a more tangible form in the larger storage vessels that are not so often handled. This stage of decomposition is mainly confined to the surface, and hence the lower stratum, when carefully separated from the supernatant fungus, is not materially damaged.
The second stage of change consists in positive fermentation whereby the syrup becomes roiled, soured, and generally stale and worthless.
The third stage of deterioration is characterized by the disappearance of the cyanhydric acid, either by evaporation or positive destruction during the fermentative decay. Another change of a peculiar kind is also often noticeable, although in itself not vicious. It seems to be due to the normal presence in the drug of a chemical ferment which rapidly changes the sugar of the syrup into an amorphous deliquescent form. This action may result from the synaptase, but it is more probably effected through a distinct agency. The objection to this species of alteration is that it renders the syrup more conducive to the positively deleterious influences above noted.
Excepting the last, all of these changes are injurious enough, but although the fermentation renders the syrup wholly unfit for use from an aesthetic point of view, the dissipation of the cyanhydric acid causes almost absolute worthlessness, from a therapeutic point of view.
Knowing the relative amount of cyanhydric that the syrup should contain, an article deteriorated simply in the loss of this agent, can be easily regenerated by the requisite addition of the acid and some oil of bitter almonds. In fact, a very definite and practical method for producing this syrup, de novo, would consist in extracting the astringency and bitterness to the exclusion of the synaptase, and completing the syrup by the addition of the known proportion of cyanhydric acid and oil of bitter almond. Since in such a process it becomes essential to employ a fresh and full strength cyanhydric acid, the writer finds it opportune to interpolate a few remarks on this subject, and finally append a formula for such a preparation.
The first formula of the Pharmacopoeia for cyanhydric acid, however excellent it may be in large operations, is not suited as a process for the shop. The second formula to be used as an alternate process expressly for the counter, is badly defective in a practical aspect, although theoretically splendid. The argentic cyanide is one of the most reluctant substances to manipulate for a body having such a bland appearance. It adheres most obstinately to everything, so that its accurate weighing and admixture with acidified water becomes almost impossible. Furthermore the layer of argentic chloride prevents a perfect decomposition, and hence the liquid ultimately contains an excess of chlorohydric acid, and a corresponding deficiency of cyanhydric acid. It is strange that the Pharmacopoeia embodied the first formula, which is in reality only adaptable to factories, and doubly strange that it did not incorporate such an excellent and simple process as that given in Fownes' chemistry. This process is equally applicable to large and small operations, and yields a definite and permanent product, and is therefore unlike that of either of the official methods. It consists in decomposing pure potassic cyanide with tartaric acid in the presence of water and alcohol, as follows:
KCy + H2T = Hcy + KHT
Pure potassic cyanide is as easily obtainable as argentic cyanide, and is ultimately cheaper. There are, strangely enough, but few among the numerous cyanides that are available for the purpose of generating cyanhydric acid fit for medicinal use. Soluble or insoluble they are mostly indefinite and intractable substances. Mercuric cyanide, which might be so useful for this purpose, is much to be regretted undecomposable by those acids, which would render the complete removal of the mercury possible. Hydric sulphide completely decomposes it, and hence the writer attempted to employ the oxysulphides of antimony for this purpose. Although these methods generated cyanhydric acid abundantly and promptly, they yet failed to precipitate the mercury completely. Owing to the great affinity of mercury for the compounds of carbonic sulphide (also called carbon disulphide), it may be that some such combination could be found to answer the purpose.
The formula for cyanhydric acid transcribed from Fownes' is as follows:
|Potassic cyanide, pure||65||parts|
|Water, sufficient to make||1538||"|
Mix the potassic cyanide and tartaric acid with 500 parts of water, in a well-stopped bottle, or dissolve each separately in 250 parts of water, and mix the solutions; then add the alcohol and sufficient more water to make 1538 parts. The alcohol may also be mixed with 600 parts of water, first the two salts be then added, and enough water to make 1538 parts as before. After the hydropotassic tartrate has subsided as a heavy crystalline powder, the clear supernatant liquid is decanted.
The yield of official acid is 1350 parts, but the generated cream of tartar weighs 188 parts, thus making the 1538 parts as above directed. The solution contains mere traces of the acid tartrate.
The Pharmacopoeia, recognizing the necessity of adding a preservative to the syrup of wild cherry, resorted to glycerin. It is, however, rather late in the day to employ glycerin for that purpose, more especially when so sparingly applied. Five per cent. of glycerin is contained in the new official syrup, but it is safe to say that 20 per cent. would not suffice in any case where there is a well-marked tendency to fermentative decomposition. Alcohol would have been amply sufficient at 4 per cent., and should have been used. The writer in this instance strongly recommends alcohol, not alone for its simple preservative effect, but since it also serves another important purpose with equal efficiency.
Several years since the writer employed an odd looking sample of bark for preparing the syrup, and found that little if any cyanhydric acid was developed. The bark possessed bitterness and astringency in moderate degree, and was therefore kept with a view to employ it in alcoholic mixtures containing wild cherry as one of the ingredients. On employing this bark on such an occasion with a 25 per cent. alcohol, cyanhydric acid was quite freely developed. This rather astonishing result showed that a moderate proportion of alcohol did not only not check the generation of the acid, but even caused its appearance where water alone had been powerless. Whilst glycerin, under such circumstances would have retarded or more or less obstructed the production of cyanhydric acid, it would not have obviated the fermentation. Subsequently the writer applied one-eighth alcohol in preparing the syrup, and found that, primarily, it prevented all deterioration, and secondarily, whilst facilitating the production of cyanhydric acid, also yielded a clearer and generally more satisfactory percolate. Substituting the glycerin in the official process by alcohol, the formula then becomes modified as follows:
|Wild cherry in No. 20 powder,||12||parts|
|Alcohol, sufficient, or||4||"|
|Water, sufficient to make||100||"|
Mix alcohol and water in the proportion of 1 part of the first and 7 parts of the latter and moisten the wild cherry with 6 parts of this mixture. Pack the moistened bark firmly into a glass percolator and pour on of the above mixture until the liquid has slowly penetrated to the bottom of the column. Now check the percolation for 24 hours by closing the exit. On resuming the operation let the current slowly flow so that in the course of 12 hours 40 parts of percolate is obtained. Pour three-fourths to four-fifths of this upon the sugar contained in a bottle and agitate occasionally until no more sugar is dissolved. Decant the clear syrup from the residuary sugar, and pour on this the remainder of the percolate, agitating again as before, until all the sugar has dissolved. Finally mix the two syrupy solutions and strain through a No. 80 sieve.
The American Journal of Pharmacy, Vol. 55, 1883, was edited by John M. Maisch.