ON PRUSSIAN BLUE 285 



SECTION XIV. ON THE CONSTITUENT PARTS OF THE COLOUR- 

 ING MATTER. 



I met by accident with a very remarkable phenomenon : 

 As I was one evening about to pour the liquor of the first 

 distillation of the colouring matter out of the receiver into a 

 bottle (Sec. vi.), and a burning candle happened to be 

 standing near the orifice, the air contained in the receiver 

 instantly took fire, without, however, any explosion. As long 

 as the mass continued warm in the receiver (for the 

 distillation was forced rather a little too much), I was able 

 to inflame this air several times, till at last it would no more 

 take fire. As all the phlogistic substances, from the 

 vegetable as well as animal kingdom, contain aerial acid as 

 one of their constituent parts, I wished to know whether 

 there was any of this acid contained in the colouring matter. 

 I therefore filled a small retort half-full with this latter, and, 

 after applying a receiver, gave it immediately a pretty strong 

 heat. The receiver soon grew hot, and as it was at the 

 same time filled with thick vapours of the colouring matter, 

 I separated it from the retort, and presented to its orifice a 

 little burning sulphur, 1 which I introduced even into its 

 cavity. The air in the receiver took fire instantly. I 

 afterwards poured some very clear lime-water into it, which 

 was immediately precipitated. Hence it may be concluded 

 that aerial acid and phlogiston exist in this colouring 

 matter. But several chemists having asserted that the 

 Prussian blue constantly yields volatile alkali upon dis- 



1 When we make use of a candle for this purpose, we can never be sure 

 that the aerial acid does not come either from the tallow or from the 

 wick. I was thus deceived several times, on setting fire to inflammable 

 air. It is therefore better to use a little brimstone fixed upon the end 

 of an iron wire. 



