Assay of Wild Cherry Bark.
By A. B. Stevens, Ph.C., and J. N. Judy, Ph.C.
Presented to the American Pharmaceutical Association, Denver Meeting, 1895.
Query No. 1.—"Is the thin, green wild cherry bark really more valuable therapeutically than the older and thicker bark?" Make comparative assays.
The therapeutic value of the bark depends upon the amount of the active principles within the bark. This principle is a glucoside, identical with or closely allied to amygdalin. Therefore, the query can be answered only by a comparison of the results obtained by the assays requested.
The thick bark occurs in the market in slightly curved or arched pieces of various sizes, the length being about 25 to 80 mm., and the breadth 13.5 to 50 mm. The thickness of the pieces which consist entirely (or nearly so) of the inner bark is about 3.15 to 4.16 mm. In cases where the outer portion of the bark is attached it is nearly or quite 6 mm. thick.
The thin bark has the principal characteristics of the thick bark, such as odor, fracture and color, which may vary somewhat, also differing in thickness, being about 2 to 2.8 mm. thick. It is also found in the market in somewhat smaller fragments than the thick bark.
Both the thick and thin barks vary in color and other external characteristics according to the size of the pieces, and the presence or absence of the periderm, etc. When the periderm is attached, the pieces are of rougher character, and in such parts of the bark the color is redder, and somewhat spotted at intervals with irregular grayish silver-white or brownish patches. Some of the smaller pieces, particularly the thin bark, presents a uniform reddish-yellow appearance, and is nearly smooth externally. Internally the bark has a deep yellowish or reddish-brown color, the color of the thick bark being the more intense. On the inner surface of the bark occasional portions of wood are found. The longitudinal fracture is close and presents a rough surface of a yellowish-gray color interspersed with reddish spots and stripes. The transverse fracture is close, somewhat rough and fibrous, and of a redder hue than the longitudinal. The texture of the bark is somewhat spongy, particularly the inner layers.
Carefully selected samples of each variety were obtained and the wood and outside rough portions removed, after which the bark was ground into fine powder and each sample placed in a glass-stoppered bottle.
The method of estimation was based upon the conversion of the glucoside into hydrocyanic acid and a volatile oil; second, upon the distillation of the hydrocyanic acid to separate it from the bark; and third, upon the estimation of the hydrocyanic acid. Two methods were used. The details of the operations are as follows:
First method.—Ten grammes of the drug were placed in a small flask, about 100 c.c. of water were added, corked tightly, macerated for twelve hours, and connected with a large condenser. A moderate heat was then applied and the distillate conducted into a solution of potassium hydroxide, the distillation being continued almost to dryness. About 150 c c. more of distilled water were added through a glass-stoppered thistle tube, and distillation continued as before. This operation was repeated not less than four times to secure the absolute removal of all the hydrocyanic acid from the drug, after which the condenser was thoroughly rinsed to remove any adhering hydrocyanic acid. The amount of acid was then estimated volumetrically, by titrating the slightly alkaline solution of potassium cyanide with decinormal silver nitrate solution.
The second method of estimation was as follows: The drug was macerated and distillation continued as in the first method, but this time the distillate was conducted into a solution of silver nitrate. An insoluble silver cyanide was formed. The precipitate was allowed to settle, the supernatant liquid decanted through small counterpoised filters, the precipitate transferred to the filter, washed, dried and weighed.
The glucoside was estimated without decomposition, as follows:
Five grammes of the drug were placed in a Soxhlet's apparatus, extracted with absolute alcohol for six hours, and the alcoholic extract evaporated to a syrupy consistence. An excess of ether was added, precipitating all the glucoside, together with some coloring matter and resin. The precipitate was washed with ether, on the filter, and treated for a short time with 100 c.c. of boiling distilled water. The solution was allowed to cool. The glucoside in solution was filtered, the filter washed with a little hot water, and the washings and filtrate mixed. The solution was evaporated to dryness in a weighed porcelain dish, and again weighed; the increase in weight represented the glucoside.
In order to test the accuracy of the above method, and to ascertain the number of distillations necessary to obtain all of the acid, the distillates were collected separately, and the acid in each estimated with the following results:
|First distillate||17.15 per cent hydrocyanic acid.|
|Second "||11.2 "|
|Third "||5.25 "|
|Fourth "||1.05 "|
|Fifth "||0.00 "|
To verify the above, a number of experiments were made by adding a known quantity of hydrocyanic acid to previously exhausted bark and to other drugs like cinnamon. These were subjected to distillation under exactly the same conditions as in the preceding case, with the following results:
|First distillate||56.0 of total acid added.|
In no case could all of the hydrocyanic acid which was mixed with the powder be recovered. The loss was about 1 per cent.
Assay of Bark.
Average results of several estimations upon each sample of the bark:
|First method, No.||1, .035||per cent. of hydrocyanic acid.|
|Second method, "||1, 0.319||"|
|First method, No.||1, 0.24||per cent. of hydrocyanic acid.|
|Second method, "||1, 0.229||"|
Yield of amygdalin (or allied substance):
Thick bark, average 4.12 per cent.
Thin bark, average 3.16 per cent.
Of the two methods given for the estimation of the acid, the first is the more accurate and satisfactory. Much care is required in manipulating the precipitate of silver cyanide in the second.
The yield of hydrocyanic acid as above stated is more than twice that previously reported. J. S. Perot (Am. Jour. Ph., Vol. 24, 1852, page III) found from 0.0478 to 0.1436 per cent. We believe that the result is due to the improved method of estimation, as numerous experiments proved that only about half of the acid was obtained during the first distillation.
The above results appear to furnish to the query a negative answer.
Ann Arbor, Mich , June 15, 1895.