And that birch sap contains sugar is known, the peasants of many countries, especially Russia, being well acquainted with the art of making birch wine by fermenting its saccharine juice.
But I find no hourly or daily record of the amount of sugar-bearing sap which can be drawn from the birch, or from any tree, before it has acquired its great digesting or rather developing and transpiring apparatus--its leaf system. And I do not know of any extended chemical analysis of sap either of the birch, or other tree.
Besides sugar, which is present in this sap to the extent of 616 grains--nearly an ounce and a half--per gallon, there are present a mere trace of mucilage; no starch; no tannin; 3½ grains per gallon of ammoniacal salts yielding 10 percent of nitrogen; 3 grains of albuminoid matter yielding 10 percent of nitrogen; a distinct trace of nitrites; 7.4 grains of nitrates containing 17 percent 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.

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