of Indigo and the Fixed Oils, 245 



alcohol • yet the indigo, so purified, when mixed with oil and 

 boiled, was found capable of imparting the crimson colour. I 

 again purified indigo in the dry way, by sublimation, and 

 boiled the crystals ''^ in alcohol, to which they imparted no tinge ; 

 but these, when boiled in oil, produced a similar colour. In- 

 digo, then, is the sole source of this crimson colour. 



My next object naturally was to investigate the immediate 

 cause of the changes ; and, for this purpose, I submitted the 

 crimson colour, made as before stated, and a cold solution of 

 oil and indigo, to the following experiments. Both solutions 

 were subjected to the same experiments, that a comparison of 

 the effects produced might lead one to discover what alteration 

 had resulted from the application of heat. 



Hot Solution. Cold Solution. 



No. 1. Became first green, and No. 1. Immediately becomes 



rapidly passing to blue and reddish green, which remains unchanged 

 bluet ended in crimson% when out of contact of the atmos- 



phere. When exposed, the surface 

 first becomes purphsh, which gra- 

 dually pervades the solution. If 

 a limited quantity of air be admit- 

 ted, the change of colour is also 

 limited. 



Muriate of Tin. 



2. Immediately lessens, and fi- 2. Lessens and removes colour, 

 nally removes colour. 



Alcohol. 



3. Removes colour. 3. Removes colour^. 



* Tliese crystals, obtained from indigo once sublimed, were viewed imder a 

 lens as powerful as was consistent with a proper quantity of light. Their form 

 appeared to be that of a four-sided prism. They were opaque, and varied in colour 

 according to the angle of light in which they were seen, changing from a light 

 copper to a reddish metallic appearance, and presenting, in different positions, 

 lilac, lightish green, pink, and pinkish white. When viewed under the direct rays 

 of the sun, they exhibited a brilliancy approaching to combustion. 



f Care must be taken not to decompose the crimson by continuing the applica- 

 tion of the heat too long. 



:|; This solution must be in its minimum state of oxygenation, otherwise all the 

 colour will not be removed. 



