'WI

GELATINOUS AND ALBUMINOUS INJECTION-MASSEs 265
400. Soluble Prussian-Blue for Injection-masses (Ranvier's
formula1).-Make a concentrated solution of sulphate of
peroxide of iron in distilled water, and pour it gradually into
a concentrated solution of yellow prussiate of potash. There
is produced a precipitate of insoluble Prussian-blue. (An
excess of prussiate of potash ought to remain in the liquid;
in order to ascertain whether this is the case take a small
quantity of the liquid and observe whether a drop of sulphate
of iron still precipitates it.) Filter the liquid through a felt
strainer, underneath which is arranged a paper filter in a
glass funnel. The liquid at first runs clear and yellowish
into the lower funnel; distilled water is then poured little by
little on to the strainer; gradually the liquid issuing from
the strainer acquires a blue tinge, which, however, is not
visible in that which issues from the lower filter. Distilled
water is continually added to the strainer for some days until
the liquid begins to run off blue from the second filter. The
Prussian-blue has now    become soluble.    The strainer is
turned inside-out and agitated in distilled water; the
Prussian-blue will dissolve if the quantity of water be
sufficient.
The solution may now be injected just as it is, or it may be
kept in bottles till wanted, or the solution may be evaporated
in a stove, and the solid residuum put away in bottles.
For injections, if a simple aqueous solution be taken, it
should be saturated. Such a mass never transudes through
the walls of vessels. Or, it may be combined with one fourth
of glycerin, or with the gelatin vehicle above described.
401. Gelatin Injection-mass (Berlin-Blue) (Hoyer's for-
mula 2).-Mix a small quantity of a very dilute and warm solu-
tion of Berlin-blue with an equally small quantity of a mode-
rately dilute gelatin solution. By this means a clear homo-
1 Ibid., p. 119.
2 ' Biol. Centralbl.,' ii (1882), pp. 19-22. 'Journ. Roy. Mic. Soc.' (N.S.),
iii (1883), p. 142.