244 Mr. Weston on the Reciprocal Action 



and passing through the different shades of light green — green- 

 ish blue — blue and blackish blue, terminates in black. 



These facts, as they shew us upon what the solubility and 

 insolubility of indigo depends, enable us fully to understand 

 how that, if we wished to make soluble the insoluble blue 

 indigo, which occupies the middle state, we must deprive it of 

 a certain quantity of oxygen, and so again render it green. 

 On these principles it would be legitimate to infer, that all sub- 

 stances which have a greater affinity for oxygen than indigo, 

 and simultaneously afford a menstruum for solution, must be 

 capable of dissolving indigo. This influence led me to consi- 

 der that, as oils possessed such qualifications, particularly when 

 heated, it was highly] probable, that in oils alone a solution 

 might be accomplished. I accordingly mixed pounded indigo 

 with cocoa-nut oil*, in a Wedgewood's evaporating dish^ and by 

 an Argand's lamp gradually raised its temperature to the boiling 

 point. The mixture became at first green, and passing rapidly 

 to blue, and reddish blue, assumed a fine crimson. 



These changes were as beautiful as they were unexpected ; 

 and on this interesting compound I instituted various experi- 

 ments, many of which it would be superfluous to mention, as I 

 have, since my return to England, found myself in a great 

 measure anticipated by Mr. Crura, in his elaborate paper on 

 Indigo, in the Annals of Philosophy for 1823. I shall, con- 

 sequently, after first making a few remarks on the substance 

 dissolved, pass on and direct my attention to a subject not 

 touched upon by Mr. C. ; namely, the immediate cause of 

 these changes. 



Indigo, in its marketable state, is, as is well known, a com- 

 pound colour. It first gives to boihng water a Madeira colour 

 with greenish tinge ; then to boiling diluted muriatic acid a 

 light brownish yellow ; and, lastly, to boiling alcohol a fine 

 bright carmine. As I had used the indigo in this impure state, 

 it was necessary first to see how these extraneous colours in- 

 fluenced the colour under consideration. The indigo was, 

 therefore, purified by water, the acetic and muriatic acids, and 



* Animal and vegetable oils are equally effectual, as one might have supposed, 

 from their containing the same ultimate products, and the same; or nearly th© 

 same; proportion of them. 



