VOL. XXXIII.] PHILOSOPHICAL TRANSACTIOXS. 7 



and best proportioned to produce the finest colour. The only misfortune he 

 takes notice of, as attending his prescript, is what may happen in the cal- 

 cination. 



It would be curious to know what gave the first hint for the production of so 

 fine a colour, from a combination of such materials ; especially when we come 

 to consider, that the blood has the greatest and principal share in this surprising 

 change. Doubtless blood of any kind, or flesh of any kind, would produce 

 the same effects, but the latter would not produce so beautiful a colour as the 

 former. Having dried some beef freed from its skin and salt, and pursued the 

 same course as with the blood, there was a sensible difference to be observed 

 during the calcination, and a very manifest one in the beauty of the 1 colours, 

 when finished. 



To prove the share the blood has in this change, the following experiments 

 may be convincive. 



The solution of alum mixed with that of the vitriol, produces no alteration 

 of colour: if to these there be added the sp. salis, the appearance is the same ; 

 but if to the whole you put the lixivium with blood, there precipitates a blue. 



If you substitute, instead of the lixivium with blood, a lixivium made with 

 the same salt of tartar only, which then becomes an ol. tartari ; and after the 

 mixture of the solution of alum, with that of the vitriol, you pour on this ol. 

 tartari, there follows indeed a precipitation, but of no colour ; and if you add 

 the spirit of salt, it so strongly attracts what is precipitated, as to render the 

 muddy mixture perfectly clear. 



The very same effect will follow, if any volatile alcalious spirit is made use of 

 as a precipitant, or any volatile salts dissolved in water; nor can the blood itself 

 be supposed to communicate this change from any such properties, the heat of 

 fire it undergoes in the calcination, being sufficient to throw them off. 



In the calcination of the dried blood and salt of tartar, it was observed, that 

 there was a loss of just half. It is difficult to determine exactly what quantity 

 of either was lost by this calcination, but it will easily be granted, that there 

 was lost a far larger quantity of the blood, than of the salt of tartar; and that 

 is obvious from an experiment, by which, wiien the salt of tartar was calcined 

 by itself, with the same degree of heat, it lost less than -i-, whereas, when the 

 dried blood was calcined by itself, it lost more than -f . 



The blood, in calcination with the salt of tartar, communicates its tinging 

 quality to the salt, or that quality is extracted from it by the salt, and passes 

 with it in its dissolution in the boiling water. 



To prove this, some dried blood was calcined by itself, and a strong decoction 

 was made of it in water, and afterwards filtered : this, when mixed with the 



