4 grains of nitrates containing 17 per cent. of nitrogen; no
chlorides, or the merest trace; no sulphates; no sodium salts; a little
of potassium salts; much phosphate and organic salts of calcium; and
some similar magnesian compounds. These calcareous and magnesian
substances yield an ash when the sap is evaporated to dryness and the
sugar and other organic matter burnt away, the amount of this residual
matter being exactly 50 grains per gallon. The sap contained no peroxide
of hydrogen. It was faintly if at all acid. It held in solution a
ferment capable of converting starch into sugar. Exposed to the air it
soon swarmed with bacteria, its sugar being changed to alcohol.
A teaspoonful or two of, say, apple juice, and a tablespoonful of sugar
put into a gallon of such rather hard well-water as we have in our
chalky district, would very fairly represent this specimen of the sap of
the silver birch. Indeed, in the phraseology of a water-analyst, I may
say that the sap itself has 25 degrees of total, permanent hardness.
How long the tree would continue to yield such a flow of sap I cannot
say; probably until the store of sugar it manufactured last summer to
feed its young buds this spring was exhausted.
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