420 PHILOSOPHICAL TKANSACTIONS. [aNNO 1 7 J Q. 



Since therefore the specific gravity of human blood is 1054, and that of its 

 serum 1030, it is plain, that blood is heavier than serum by about one part in 

 43. From which it follows, that the globular part of the blood is specifically 

 heavier than the serum, since the globular part being separated from the blood, 

 leaves the remainder, or tlie serum, specifically lighter than the entire mass. 



But in order to determine the exact specific gravity of the blood globules, it 

 is first necessary to know the proportion which the whole quantity of the 

 crassamentum contained in blood bears to the serum. To this end Mr. Boyle 

 has given two several observations of the weights of the crassamentum and 

 serum, after they have separated one from another in the porringer. But be- 

 sides the difficulty of making this experiment with any tolerable exactness, it is 

 to be considered, that there is a great deal of serum contained in the interstices 

 of the globules, that compose the crassamentum. 



This difficulty however is in some measure answered by two other experi- 

 ments, which Mr. Boyle made for this purpose, after the following manner. He 

 put a quantity of the crassamentum, already separated from the serum, into an 

 alembic, and distilled off the remaining serum to dryness, but without drawing 

 off the oil, or volatile salt ; after which he weighed the distilled liquor, and the 

 dry mass left behind. 



By comparing these experiments with the two former, it will be found that 

 the entire weight of serum contained in blood, is nearly -H- of the whole, and 

 consequently the weight of the dried crassamentum is only -iVths of the 

 blood. 



But for further satisfaction, an analysis was made at my desire with a large 

 quantity of blood, amounting to 4lbs. 14 oz. by that ingenious and skilful 

 chemist, Mr. John Brown. From this was obtained, with a very gentle heat, 

 2lbs. 14 oz. 6 dr. of a phlegmatic liquor, which had scarcely any thing of the 

 foetid scent usual in the distillation of animal substances ; and its specific 

 gravity was nearly the same with that of common water, being only 1000,8. 

 This being mixed with a strong solution of alum, scarcely afforded any coagu- 

 lum ; but exhibited a considerable one on mixture with a solution of Roman 

 vitriol. 



The distillation being continued with the same heat, we had 7 oz more of 

 phlegm considerably impregnated with volatile salt, as was manifest from the 

 smell. The specific gravity of this was 1007 ; and having mixed it with tinctura 

 martis optima, solution of alum, and of Roman vitriol, a large coagulurn was 

 precipitated. In distilling these, there were lost by evaporation, 2 oz. 2 dr. 



The third portion of liquor, being raised with a stronger fire, amounted to 

 7 oz. 6 dr. This was reddish, and turbid, and so strongly charged with volatile 



