THE MICROTOMIST 'S VADE-MECrUM

Take of carmine and of picric acid equal parts by
weight.
Dissolve the picric acid in one hundred times its weight of
water (using heat if necessary).
Dissolve the carmine in fifty times its weight of strong
ammonia.
Mix the two solutions. Use porcelain evaporators and
glass funnels.
The best results were obtained when the solutions were made
at the ordinary temperature of the laboratory, 17' C., and
then evaporated three-fourths at a temperature of 40-450 C.
The solution should be allowed to cool, and be filtered through
two thicknesses of filter paper. The filtered liquid is then
evaporated to dryness at 400 C. or at the ordinary tempera-
ture. The residue, dissolved in one hundred times its weight
of water, should give a clear solution after filtering.
Make 50 c.c. of such a solution and filter it through two
thicknesses of filter paper and a fine cotton filter moistened
well and crowded into the neck of the funnel. Filter the
solution four or five times through the same filter, and a clear
solution will probably be obtained. (Sic. I am here copying
verbatim from the ' Journ. Roy. Mic. Soc.' If it should appear
difficult to understand why 50 c.c. of a clear solution should
be subjected to all this filtering in view of " probably " obtain-
ing " a clear solution," it may be well to suppose that in
directing us to take 50 c.c. " of such a solution " the writer
means simply to direct us to take a watery solution, not neces-
sarily clear, and to filter it t us if not clear.) The writer
continues :-In case a clear saltion cannot be obtained by
repeated filtering the whole of the powder may be dissolved
in the proportion given above and allowed to stand a few days
in a tall narrow vessel.   If the finely-suspended particles
settle, the top will be clear and may be decanted, but if the
fluid remains cloudy a quantity of ammonia equal to that
originally used should be added to it, and the evaporation of

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