Ash.—The ash is determined by ignition at the lowest possible temperature, best in a muffle ([28-32]). The ash should be examined qualitively. Where a quantitive analysis is desired, larger quantities of the extract are incinerated and the constituents of the ash determined in the usual way.[389]
Total Nitrogen.—Since nitrates are not present unless added in the manufacture, the total nitrogen is best determined by moist combustion.[390]
Nitric Nitrogen.—The extract should be tested for nitrates and if present they are determined in the manner already described.[391]
Ammoniacal Nitrogen.—When ammonia is present it is determined by distillation with magnesia.[392]
Since boiling with magnesia may cause the distillation of more ammonia than is present as ammonium salts, the plus being due to the decomposition of some other nitrogenous compounds, Stutzer replaces the magnesia with barium carbonate.[393]
Proteid Nitrogen Insoluble in Sixty-Two Per Cent Alcohol.—The aqueous solution is treated with strong alcohol until the mixture contains about sixty-two per cent of the reagent. The precipitate produced is separated by filtration, washed with sixty-two per cent alcohol and the nitrogen therein determined.
Albumose Nitrogen.—This is secured by saturating the aqueous solution with zinc or ammonium sulfate. The separated albumoses are skimmed from the surface, thrown in a filter, washed with a saturated solution of zinc sulfate and the nitrogen determined therein by moist combustion. In the filtrate from the above separation, peptone is detected qualitively by adding a few drops of dilute solution of copper sulfate (biuret reaction).
Kreatin, Kreatinin and Other Flesh Bases.—The clear, aqueous solution of the extract is acidified with sulfuric, mixed with a solution of sodium phosphotungstate and allowed to stand for about six days. The precipitate is collected, washed with a solution of the precipitant, and the nitrogen therein determined. The nitrogen found, less that due to ammonia, represents the total nitrogenous matter precipitated by the phosphotungstic acid. From this quantity is deducted the nitrogen in the proteids, precipitated by sixty-two per cent alcohol and by ammonium or zinc sulfate, and the remainder represents the nitrogen in flesh bases.
The nitrogen thrown out by the phosphotungstic acid is deducted from the total nitrogen, and the remainder represents the nitrogenous bodies not precipitable by the reagent named.
This method of separating the nitrogenous matters in meat extracts is based on the observation that these bodies contain at most only a small quantity of peptones, so small as to be safely negligible.[394]