COAL-TAR COLOURS IN GENERAL       105

CHAPTER XIII.
COAL-TAR COLOURS IN GENERAL.
to    134. The following "Classified List of the chief Anilin
of Dyes, with their Solubilities in Water and in Spirit" (page
a 106) is taken from    a paper by Dr V. Harris in 'Quart.
r Journ. Mic. Sci.' (N.S.) xc (1883), p. 301.
' 135. Coal-tar Colouring      Matters.   Anilin   Stains.-It
would be out of place here to attempt an exposition of the
extremely complicated chemistry of the coal-tar colours, and
the reader is referred for information on that subject to the
of treatises on the chemistry of dyeing and of the carbon coni-
(LJ  pounds in general. (The following books are recommended:
4   Bolley, ' Die chemische Technologie der Spinnfasern, &c.,
,ii  Fortgesetzt von Kopp and Meyer,' and Schultz, 'Die Chemie
des Steinkohlentheers,' &c., Braunschweig.)
It is more important for us to note those general proper-
1   ties of the anilin dyes that have relation to their applicability
to histological staining processes.   The great advantages
offered by the majority of these dyes are that they stain most
1   animal tissues almost instantaneously and with great bril-
liancy, whilst the stain readily takes effect on tissues
hardened in chromic acid, which latter is, as we shall see, in
certain cases a very important point. A decided disadvantage
attaching to the whole group is the doubtful permanence of
the stain, and a further disadvantage of most of them is that
the stain is extracted by alcohol, or by the clearing media,
4",~