689 
differences in colour and shape and the erystals also differ in respect 
to other reagents and solvents, as will be further indicated, it may 
be assumed that the phenomenon is connected with differences of a 
chemical nature. 
The action of concentrated sulphuric acid on dried preparations 
shows no trace of the different behaviour of the crystals with regard 
to sulphuric acid. The reaction takes place so quickly that it some- 
times completely escapes observation. The treatment of dried prepar- 
ations with concentrated sulphurie acid is to be deprecated, for such 
a method of working greatly decreases the value of the elegant 
reaction, which is so well suited for microscopical investigation. 
The bright colour which the reaction produces is usually called 
blue, sometimes also blue-violet. It may be called blue, although a 
faint violet shade is sometimes unmistakable (compare KLINCKSIECK 
et VaLerrm, Code des Couleurs, 426 and 451). 
I have found no explanation of the reaction in the literature. 
Husmmann ') states that water causes the blue colour to disappear and 
unchanged carotin remains. If the blue crystals are treated with a 
large quantity of water, then they resume their original colour, 
orange-yellow or red. Sulphuric acid brings the blue colour back again. 
The objects with which I have studied the sulphuric acid reaction 
in the manner described are the same as those with which Morrscn’s 
potash method was investigated (see the list in the first communication). 
Zine chloride and Antimony trichloride. 
It is not only with somewhat diluted sulphurie acid, but also with 
saturated solutions of both zine chloride and antimony trichloride 
in 25°/, hydrochloric acid that the crystais of the carotinoids which 
occur naturally in the cells or are artificially produced there, can 
be given a beautiful dark, persistent, blue colour. These two solutions 
have hitherto not been used as reagents for carotinoids. [ tried them 
in about twenty cases. I allowed the solutions to flow to the prepa- 
rations under a cover-slip. When a solution of zine chloride was 
used, the preparations lay in water, but when I used a solution of 
antimony trichloride I first placed them in dilute hydrochloric acid 
in order to obviate the formation of insolulable antimony oxychloride. 
The reaction did not occur equally quickly in the case of all the 
crystals. The orange-yellow crystals become blue before the red ones. 
When the zine chloride solution was used the red erystals did not 
1) A. HuseMANN, Ueber Carotin und Hydrocarotin, Ann. der Chem. u. Pharm. 
Bd. CXVII, 1861, p. 226. 
