Full resolution (JPEG) - On this page / på denna sida - II. The Protein Substances - I. Simple Proteins - C. Cleavage Products of Simple Proteins - 1. Albuminates
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126 THE PROTEIN SUBSTANCES.
concentrated protekl solution, such as blood-serum or egg-albumin, the
alkali albuminate may be obtained as a solid jelly which dissolves in
water on heating, and which is called " Lieberkuhn’s solid alkali
albuminate." By the action of dilute caustic alkali solutions on dilute
proteid solutions we have alkali albuminates formed slowly at the ordinary
temperature, but more rapidly on heating. These solutions may vary
with the nature of the proteid acted upon, and also with the intensity
of the action of the alkali, but still they have certain reactions in common.
If proteid is dissolved in an excess of concentrated hydrochloric acid,
or if we digest a proteid solution acidified with 1-2 p. m. hydrochloric
acid in the thermostat, or digest the proteid for a short time with
pepsin-hydrochloric acid, we obtain new modifications of proteid which
may show somewhat varying properties, but have certain reactions in
common. These modifications, which may be obtained in a solid gelat-
inous condition on sufficient concentration, are called acid albuminates
or acid albumins, and sometimes syntonin, though we perfer to apply
the term syntonin to the acid albuminate, which is obtained by extract-
ing muscles with hydrochloric acid of 1 p. m.
The alkali and acid albuminates have the following reactions in
common: They are almost insoluble in water and dilute common-salt
solution (see page 104), but they dissolve readily in water on the addi-
tion of a very small quantity of acid or alkali. Such a solution as nearly
neutral as possible does not coagulate on boiling but is precipitated at
the normal temperature on neutralizing the solvent by an alkali or an
acid. A solution of an alkali or acid albuminate in acid is easily pre-
cipitated on saturating with NaCl, but a solution in alkali is precipitated
with difficulty or not at all, according to the amount of alkali it contains.
Mineral acids in excess precipitate solutions of acid as well as alkali
albuminates. The nearly neutral solutions of these bodies are also pre-
cipitated by many metallic salts.
Notwithstanding this agreement in the reactions, the acid and alkali
albuminates are essentially different, for by dissolving an alkali albumi-
nate in some acid no acid, albuminate solution is obtained, nor is an alkali
albuminate formed on dissolving an acid albuminate in water by the
aid of a little alkali. In the first case we obtain a combination of the
alkali albuminate and the acid, soluble in water, and in the other case a
soluble combination of the acid albuminate with the alkali added. The
chemical process in the modification of proteids with an acid is essentially
different from the modification with an alkali, hence the products are
of a different kind. The alkali albuminates are relatively strong acids.
They may be dissolved in water with the aid of CaC03, with the elimina-
tion of ( ’<>_>. which floes not occur with typical acid albuminates, and
they show in opposition to the acid albuminates also other variations
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