I 



442 Count Le Maisirc's Memoir on [Drc. 



of herbs, and soon passes into a perfect blue. The residual 

 liquid, when there is an excess of cochineal, preserves its red 

 colour ; the prussic acid taking only the quantity necessary for 

 its saturation. 



IV. Prussiate of Charcoal. 



As all the substances of which I have spoken contain a 

 great quantity of charcoal, it was natural to try the same thing 

 with this last substance. To obtain a charcoal in a state of 

 minute division, 1 charred white paper free from size by putting 

 it into concentrated sulphuric acid, and exposing the acid to 

 heat. The black matter thus formed was diluted with a great 

 deal of water, and decanted without filtration into a matrass, 

 which I placed over the flame of a spirit of wine lamp. I then 

 poured into it while boiling a portion of prussiate of potash, and 

 the mixture became dark green. The prussiate did not assume 

 a blue colour till after eight days exposure to the air. That the 

 aper may be completely charred by the sulphuric acid, it must 

 e slightly moistened before being plunged into it. 



This, however, was not a pure prussiate of charcoal ; for as 

 the sulphuric acid chars the paper without effervescence and 

 without smell, this species of solution contains all the principles 

 of the ligneous substance. 



To obtain a pure prussiate of charcoal, I took 30 gr. of the 

 charcoal of the birch which had remained for a fortnight in an 

 alkaline ley. I pounded it while still moist upon an unpolished 

 piece of glass, with concentrated sulphuric acid. I put altoge- 

 ther three ounces of water, and boiled the mixture in a matrass. 

 I then added to the liquid 60 gr. of prussiate of potash, continued 

 the boiling for about an hour, adding water in proportion as it 

 evaporated, A dark-green prussiate was formed, which became 

 blue after five or six days exposure to the air. 



If the dried prussiate is not of as fine a blue as the best prus- 

 jsian blue, it must be repeatedly moistened and dried, which will 

 produce tlie colour desired. 



When the process was repeated with muriatic acid instead of 

 sulphuric, the result was the same ; but when newly formed char. 

 poal was employed, no combination took place. 



The formation of this prussiate was accompanied with frequent 

 anomalies, depending doubtless on the different states in which 

 the charcoal is at the time in which it is employed, and upon 

 minute circumstances which I probably overlooked, If instead 

 of boiling the mixture for an hour, as I have described, it be 

 poured after two minutes boiling into a bottle furnished with a 

 ground-stopper, and placed well corked in a stove heated to 

 122° or 144°, it will be found completely formed after an interval 

 of eight or ten hours. I put my bottles in the evening into a 

 Russian stove, and next morning found a green prussiate 

 formed. 



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