FORMATION OF INDIGO-BLUE. 193 



believe that the oxygen of the atmosphere has any influence 

 in producing decomposition, at least at the usual tempera- 

 ture, and though I have generally in the last instance eva- 

 porated in vacuo, I think the evaporation may just as well 

 be conducted in the aiN Notwithstanding all precautions, 

 however, it is difficult to avoid some portion of the substance 

 becoming changed during evaporation. 



The body, the preparation of which I have just described, 

 I propose to call Indican* By evaporation of its watery 

 solution it is obtained in the form of a yellow transparent 

 glutinous residue, which can only be rendered dry by spread- 

 ing it out in thin layers and leaving it for some time in 

 vacuo over sulphuric acid. On attempting to dry it in the 

 waterbath, it immediately undergoes a complete alteration. 

 Its taste is slightly bitter and nauseous. Its solutions have 

 always an acid reaction, but whether this reaction is peculiar 

 to it in an absolutely pure state, I am unable to say. When 

 heated in a tube it swells up and gives fumes which condense 

 to a brown oily sublimate, in which after some time a white 

 crystalline substance is formed. When boiled with caustic 

 alkali it evolves ammonia. Its compounds have a yellow 

 colour. With caustic alkalies, baryta, and lime water, the 

 watery solution turns of a bright yellow. The alcoholic 

 solution gives with sugar of lead a bright sulphur-yellow 

 precipitate, which is increased by the addition of ammonia. 

 The watery solution gives no precipitate with acetate ot 

 lead, until ammonia is also added. Its most remarkable and 

 interesting property, is that of yielding indigo-blue when 



• Ab the termination an has not yet been applied by chemists to designate 

 any peculiar class of bodies, I propose to restrict it to the names of such sub- 

 stances of a complex constitution, like rubian, as are direct products of the 

 vital energy of plants or animals, and which by their decomposition give ris« 

 to one or more series of organic compounds of a simpler constitution. In 

 applying it, it will of course be necessary, carefully to ascertain, that the sub- 

 stance to be named is really a proximate constituent of some organism and not 

 itself the result of any process of decomposition either within or out of th« 

 organism, that it is an educt and not a product. 



2 B 



