ON SYRUP OF WILD CHERRY BARK. 163 
with twice its weight of sugar, and with the other an equal 
weight was used, and the syrups* which they yielded were 
placed in a warm situation, similar to that of the preceding 
experiments. In twelve days the least concentrated com- 
menced fermenting, and was soon covered with mould, and 
the other underwent the same change shortly after. 
To test whether the tannin in wild cherry bark syrup 
played any part in preventing its fermentation, a syrup was 
made with an infusion of white oak bark, precisely like the 
preceding, and divided into two parts; to one was added 
five drops per ounce of hydrocyanic acid, containing four per 
cent., the other was left without addition. In a few days 
the latter commenced to ferment and soon spoiled, whilst 
that containing the hydrocyanic acid remains unchanged, 
notwithstanding its exposure to the great heat of last sum- 
mer. 
Syrup of Seneka snake root, which is always difficult to 
keep in summer, is entirely freed from a disposition to fer- 
ment by the addition of a little hydrocyanic acid. 
When hydrocyanic acid is added to a mixture of yeast, 
sugar and water, all tendency to fermentative change is 
suspended, and the power of the yeast destroyed during the 
presence of the acid. 
These facts are stated merely to illustrate the position 
that the ready keeping of a syrup of wild cherry bark, made 
without heat, is due solely to the hydrocyanic acid which 
enters into its composition, — and not with a view to this 
acid being used as a preservative agent, which of course its 
deleterious qualities entirely precludes. 
As the above experiments prove conclusively that there 
is no objection to reducing the proportion of sugar in this 
syrup on the score of preservation, and as an excess of sac- 
charine matter is often objectionable, it is recommended 
that the proportion of sugar to the infusion be as five to 
three instead of as six to three, as at present, which will 
increase its strength and render its manufacture more easy. 
