ON PRUSSIAN BLUE 243 



may be effected by means of an acid. After different trials, 

 I found the following method the best: 



SECTION IX. 



To 2 oz. of powdered Prussian blue, and 1 oz. of calx 

 of quicksilver, prepared by means of nitrous acid, I added 

 6 oz. of water in a cucurbit ; I boiled this mass for some 

 minutes with constant agitation, when it assumed a yellowish 

 grey colour. I then poured it out on a filter, and upon 

 what remained in the filter I poured 2 oz. of hot watdr, 

 in order to elixiviate the whole thoroughly. The strained 

 mercurial solution was then poured upon 1J oz. of iron 

 filings, free from rust, and contained in a glass vessel, there 

 being added 3 drms. of concentrated vitriolic acid. The 

 whole mass was well agitated, during which, in a few 

 minutes, it was turned quite black by the reduced quick- 

 silver, and thereby completely lost its quicksilver taste. It 

 at the same time acquired the peculiar smell of the colouring 

 matter. I left the mixture a few minutes at rest ; then 

 poured off the clear liquor into a retort ; and distilled the 

 fourth part of it off into a well-luted receiver. Here I 

 obtained the same colouring matter as from the neutral salt, 

 Sec. vi. It is sufficient to distil off one-fourth ; for this 

 matter is much more volatile than water, and goes over 

 first. 



SECTION X. 



A slight vestige of vitriol easily appears in this (Sec. 

 ix.), as well as in the preceding distillation of the neutral 

 salt, Sec. vi. This little vitriolic taint must consequently 

 be likewise separated from the colouring matter. I have 

 remarked (Sec. I.) that aerial acid is capable of dislodging 



