THE MICROTOMNIST'S VADE-MECUMT

Objects may be stained either before imbedding or after       peo
cutting. Carmine and heematoxylin both stain well sections          l
that have been cut in this mass.                                (as1,
242. Transparent Soap (Kadyi's formula 1).-Twenty-five        jg I
grammes of shavings of stearate of soda soap (any stearate of   jioed
soda soap will do, but the most to be recommended is the        ispev
sort known in commerce as " weisse Wachskernseife ") are         el
heated in a retort with 100 c.c. of 96 per cent. alcohol over a  ielts
water-bath until the whole is dissolved. Filter if necessary.    Isiert
If a drop of the solution be now poured into a watch-glass it    slliAk
will be seen that it almost immediately solidifies into a white  ard
mass. This is not what is wanted, and is a sign that the solu-   vilebt
tion does not contain water enough. Small quantities of          y.fh
water are therefore added by degrees to the solution, and         ss
the effect tested from time to time by pouring a drop of the     phi
mixture into a watch-glass. The mass will be seen to become      hai
more and more pellucid until a point is reached at which         DOtat
it is almost perfectly transparent, with merely the slightest   tl %
blue opalescence. The preparation of the mass is then com
plete.                                                           soaktio
It is not possible to state a priori the exact proportion of   pR
water that should be added, as this naturally depends on the     bow
amount of water already present in the sample of soap taken.     Mree
In very many cases it will be found that for about 120 g.        compo
soap solution, 5 to 10 g. of water will be required.             Suc
It is necessary to be very cautious in adding the water, as     E14
if too much be taken the mass solidifies more slowly or not at
all. The greatest amount of elasticity and consistency is
possessed by the mass at the moment in which it contains
exactly the minimum amount of water necessary to make it
transparent.
The reasons for this process are explained as follows. Stea-  0l
rate of soda soap is soluble in divers proportions in warm
alcohol. On cooling, the solution    either solidifies into a
' Zoo]. Aiz.,' 37 (1879), vol. ii, p. 477.

180


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