252 Proceedings of Royal Society of Edinburgh. [sess. 
measured off into a glass tube, and the drop of blood to be tested is 
allowed to flow into the tube as well. The drop of blood does not mix 
with the solution, having a different surface tension from it, and floats 
on its surface as a tiny red globule. The graduated pipette is now 
filled with solution (B) and this is allowed to run slowly into the 
mixing tube, shaking after each addition. As (B) flows in, the 
specific gravity of the mixture is lowered, and after each addition 
and shake the red globule returns more and more slowly to the 
surface. At last it neither tends to rise nor sink, and the mixture 
now has the specific gravity of the blood itself. The specific 
gravity of the mixture can readily be calculated, or found from 
the table attached to the apparatus made by Mr Fraser, Lothian 
Street. Suppose 0*5 cc. of (B) has been added, the total weight of 
the fluid divided by its volume will give the specific gravity of the 
mixture. - 
1 cc. at sp. gr. 1070 = 1070 
*5 cc. at sp. gr. 1020 = 510 
1-5 ) 1580 
1053 
As the mixtures of benzyl chloride and toluol expand with heat 
they will yelvj in their specific gravity, so that a correction for 
temperature must be made if exactitude is required. The solutions 
(A) and (B) are prepared at the temperature of 15° -6 Centigrade or 60° 
F. and if the temperature of the room in which the experiment is 
made is also 60° F. no correction will be needed. If, however, the 
temperature is higher than 60° F. the specific gravity of the fluids 
will be lower, and this fall of specific gravity will be at the rate 
of 1° for every 2° F. 
Example 1 cc. of (A) at 1070 = 1070 
•5 cc. of (B) at 1020 = 510 
1*5) 1580 
1053 
Temperature of room 66° F., therefore 3° * must be subtracted 
the real specific gravity of the mixture (and therefore of the blood) 
being 1*050 at that temperature. 
* The more accurate allowance for temperature is *88° sp. gr. for every 2° F. 
of temperature above 60°. For all ordinary purposes 1° sp. gr. is sufficiently 
accurate and more easy to calculate, and hence that figure is given in the text. 
