IN USE AT THE ROYAL BOTANIC GARDEN. 233 
II. BY SOAKING BEFORE FINALLY PRESERVING IN SOLUTIONS 
WHICH PREVENT THE FORMATION OF DISCOLOURING 
SUBSTANCES. 
1. Methods which do not render the specimen flaccid. 
a. Acid Alcohol. 
The plants are placed in strong go per cent. alcohol, to which 
has been added 2 per cent. by volume of. hydrochloric acid. 
They are then exposed as much as possible to sunlight. If the 
spirit becomes discoloured it is changed, clean acid alcohol being 
substituted for the discoloured spirit removed. When bleached 
the specimen is left in the acid alcohol permanently or it is trans- 
ferred to ordinary non-acid alcohol. In the latter case some 
specimens exhibit a tendency to darken, but this discolouration 
is not so great as when the preliminary acid alcohol has been 
omitted. 
The acid alcohol has a macerating action on delicate structures, 
and the subsequent handling of such is attended with some risk. 
It should be remembered also, when specimens bleached in this 
way are subsequently mounted, that photoxylin does not hold 
specimens to the mounting glass satisfactorily if any acid is 
present in the final preservative. Specimens, therefore, treated 
with acid alcohol should be washed free from acid in several 
changes of non-acid alcohol before being finally mounted if 
photoxylin is to be employed. Nitric acid and sulphuric acid 
have been used in the same way but with less success. 
6. Potassium Chlorate. 
Crystals of potassium chlorate are placed at the bottom of the 
jar containing the specimen and nitric or hydrochloric acid is 
added in small quantities, only sufficient to cover the crystals, by 
means of a pipette, precautions being taken to keep the acid from 
mixing with the spirit and from coming in direct contact with 
the specimen. 
The chlorine liberated rises through the spirit and has a slight 
bleaching action. The process is not so effective as that given 
above. 
1 Hugo de Vries, Berichte du deutschen botanischen Gesellschaft, vii. 
1889, p. 298. 
