688 
57 and 47'/,°/,. | have experimented with sulphuric acid of varying 
strength in about forty cases with flowers, leaves and algae. The 
carotinoids, which rarely in nature occur in crystalline form, were 
previously separated out as crystals by means of Morisca’s reagent, 
and were successfully obtained, except in a few cases. | allowed the 
sulphuric acid to flow to the preparations which were in water 
under the cover-slip or I applied it to the preparations which lay 
in a minimal quantity of water on a slide, Mixing therefore always 
took place between the mixture used and the water in which the 
preparations were, and consequently there was a slight dilution of 
the mixture. The result of this series of experiments was that the 
fine blue coloration due to sulphuric acid was always shown. In 
most cases the reaction succeeded already with sulphuric acid of 
65'/, or 76°/,, it was seldom necessary to use sulphuric acid of 
85'/, °/,, and in some cases the blue colour appeared on using sulphuric 
acid of 57°/,, eg., in Narcissus Pseudonarcissus and Cladophora. 
When stronger sulphuric acid, namely, 95°/, is used, various 
subsidiary phenomena generally occur. Sometimes the crystals are 
seen to dissolve, forming blue cloudlets in the fluid, or they lose 
their shape and unite to form blue drops of liquid. Sometimes they 
dissolve and in their vicinity a precipitation of small blue drops is 
seen. Often the blue coloration is observed to become fainter and 
disappear. Commonly some of these phenomena occur together. It is 
difficult to say to what extent the differences in the action of sul- 
phurie acid are caused by accidental circumstances or are connected 
with the chemical nature of the carotinoids, but it is certain that in 
the course of the reaction the latter plays an important part. 
It happens, for example, in many plants, that in the same cells 
two kinds of erystals are separated out, which behave differently with 
regard to sulphurie acid. Before the action of sulphuric acid takes 
place, the two kinds of erystals can already be distinguished by their 
colour and shape, especially by the colour, which is orange-yellow 
or orange, and red or orange-red. The difference is, that the blue 
colour does not appear equally quickly in both kinds of crystals or 
indeed that a different degree of concentration of the sulphuric acid 
is required to produce it. Under the action of sulphuric acid of 66'/, 
or 76°/, the orange-yellow or orange crystals are immediately coloured 
blue and the red or orange-red ones not at all or much later. When 
these different crystals have about the same thickness and are in 
proximity in the same cells, it may be assumed that the action of 
the sulphuric acid takes place under the same conditions. Since the 
different behaviour with regard to sulphuric acid is accompanied by 
