ON PRUSSIAN BLUE 289 



was, into 8 oz. of water. I now filtered the first lixivium, 

 and trying it in the ordinary way, with vitriol of iron and 

 acids, it yielded little or no Prussian blue (or at least not 

 any sensible quantity) ; but it would perhaps have yielded a 

 little if the fire had been pushed till the mass ran into 

 fusion. I now filtered the second lixivium, and tried it in 

 the same manner, with vitriol of iron, which immediately 

 grew yellow, as if lixivium sanguinis had been added ; and 

 on adding a sufficient quantity of acid the same phenomena 

 were observed as the best lixivium sanguinis would have 

 produced, and a great quantity of Prussian blue was pro- 

 cured. I mixed plumbago with the same alkali, and, pro- 

 ceeding in the same manner with sal ammoniac, obtained a 

 middling lixivium. From these experiments it appears 

 that the volatile alkali is capable of uniting with the 

 carbonaceous matter, after it has been subtilised by a strong 

 heat ; that it thus acquires the remarkable property of com- 

 bining so firmly with alkali of tartar, as to be able to support 

 the most violent degree of heat (Sec. XL (&)) ; and when this 

 alkali is dissolved in water, there is obtained lixivium 

 sanguinis, as it is called. It is now easy to explain what 

 happens in the distillation of Prussian blue, as well as of the 

 other above-mentioned metallic precipitates (Sec. xv. ()-(/)). 

 In the distillation of Prussian blue, for instance, the calx of 

 iron attracts a portion of phlogiston from the colouring 

 matter. The aerial acid being thus disengaged, must go over 

 into the receiver with the volatile alkali, which is set free at 

 the same instance ; but as the calx of iron in the heat of 

 this distillation cannot unite with more phlogiston, a portion 

 of the colouring matter, not decomposed, must likewise 

 arise. If the calx of iron could combine with the whole of 

 the phlogiston, there would come nothing over into the 

 receiver but aerial acid and volatile alkali. In order to 

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