418 PHILOSOPHICAL TRANSACTIONS. [aNNQ 17 JQ. 



To prevent the objections, which may arise for want of experiments made in 

 the same manner with Mr. Boyle's, as well as for the satisfaction of the curious, 

 who may be desirous to know the true specific gravities of serum and blood, I 

 shall proceed to demonstrate them by hydrostatical experiments. 



Exper. 5. — November, having suffered a quantity of my own blood to stand 

 about 24 hours in the porringer, and then drawing off the serum carefully with 

 a small siphon into a convenient glass, I found, by the hydrostatical balance, 

 its specific gravity to be to that of water, as 102Q,8 to 1000. 



Exper, 6. — February, I examined the serum from the blood of another per- 

 son in the same manner, and found its specific gravity to be 1028,6. 



Exper. 7, 8, Q. — In April, I procured three several quantities of serum from 

 the blood of different persons. The first of these was of a deep colour, in 

 dining something to red, and a little turbid : its specific gravity was 1029,7. 

 The second was likewise a little turbid, and of a pale whitish colour : and its 

 specific gravity was 1030,2. The third was perfectly clear, and of the colour 

 of canary : and its specific gravity was 1030. 



Though these five several experiments were all carefully made, and with a 

 balance of great accuracy, yet for further satisfaction I make the following after 

 another manner. 



Exper. 10. — In Jan. I drew off all the serum from 5 or 6 several porringers 

 containing the blood of different persons. This I found to be a little tinged 

 with blood, which was occasioned by my being obliged to draw it off pretty near 

 to the bottom of the porringers, in order to obtain a quantity sufficient for my 

 purpose. For this reason I suffered it to stand about two days, in which time 

 the globular part of the blood was entirely precipitated to the bottom, and the 

 serum was become perfectly fine and transparent. I then drew it off with a 

 siphon into a glass phial with a narrow neck, which I filled to a certain mark 

 made in the neck for that purpose. I then placed the phial in a pair of nice 

 scales, in which I had a counterpoise for the weight of the phial, and found 

 that quantity of serum to weigh 2284^ grains. Then pouring out the serum, 

 I filled the phial with common water to the same mark, and found the weight 

 of the water to be 2219 grains. From which it follows, that the specific 

 gravity of this serum was 1029,4. 



Exper. 1 1 . — In July I procured a quantity of blood taken from the temporal 

 artery, from which I drew off the serum the next day, and weighing it in the 

 same manner, found its specific gravity to be 1028,8. 



These experiments agree so nearly together, that the little difference between 

 them may very well be attributed to that which is between the serum of differ- 

 ent persons ; or to the variations occasioned by heat and cold in the several 



