8 I'HILOSOI'HICAL TRANSACTIONS. [aNNO J 724. 



former solutions, produced little or no alteration ; but on the addition of the 

 sp. salis, changed to an amber colour, without any precipitation. 



When this liquor was mixed with the ol. tartari, and poured to the former 

 solutions, it caused a precipitation, but no colour; an'd the sp, salis, as in the 

 other experiment, made the liquor clear again, but left this also of an amber 

 colour. 



The change of colour is not effected in any of the materials, except in that 

 of the solution of vitriol ; so that the alum seems only to be of use in fixing 

 the colour, as it is often used by the dyers for that purpose; and the sp. salis 

 gives it a deeper dye. For if the lixivium with blood be poured to the solution 

 of alum alone, there will fall a sediment a little on the purple ; to which if you 

 add the sp. salis, it changes the colour, and the sediment is brown. 



So much the same changes will be produced, if you pour the sp. salis to the 

 lixivium, but not the least appearance of a blue :, whereas, as is beforemen- 

 tioned, when the lixivium is poured to the solution of vitriol, there immediately 

 follows the blue, which is still heightened by the addition of the sp. salis. 



It will not be improper to take notice, that as the author orders all the 

 liquors, except the sp. salis, to be boiling hot when mixed, so it is certain the 

 colour is thereby more immediately produced, and looks more beautiful ; but 

 most of the experiments here mentioned were made with the liquors cold, and 

 the colours came to their beauty with a little washing. In one of the experi- 

 ments with the liquors cold, after the lixivium with blood had precipitated the 

 blue in the mixture of alum and vitriol, by pouring in a little more of the 

 lixivium, the blue all disappeared, and an ugly muddy colour was left ; but the 

 addition of the sp. salis soon discharged that, and the blue returned. 



In calcining the beef and salt of tartar, the matter left in the crucible weighed 

 just half of the whole mixture, as in that with the blood ; but after boiling it 

 in water, the residuum in the filtrc when dried, was very near a third less in 

 proportion than the other. From whence may be reasonably inferred, that the 

 salt of tartar holds a larger share of the beef in the one operation, than of the 

 blood in the other. 



Having, in the former part of this account of the Prussian blue, proved, by 

 the experiments there mentioned, that the solution of vitriol was the only sub- 

 ject among those ingredients, that the lixivium of blood produced this change 

 of colour in it ; and having since considered that the vitriol used in this pre- 

 paration, is no more than iron dissolved by a liquor running from the pyrites, 

 when exposed to the weather, which is afterwards boiIe<c< up and shot into 

 crystals; it-seemed to follow, as a natural consequence, that this metal is the 

 subject on which the lixivium of blood produces the change ; and this thought 



