CHAP. IV.] THE BLOOD. METHODS OF RESEARCH. 



177 



If a plaster of Paris slab (see p. 26) be imbued with such a solution 

 of litmus, a drop of blood or of blood-serum will be surrounded 

 at its edges by a distinct blue ring. In order to determine the degree 

 of alkalinity, a standard solution of tartaric acid may be made 

 by dissolving 7'5 grammes of crystallized tartaric acid in 1000 c.c. 

 of water ; one cubic centimetre of this solution should exactly 

 neutralize 0'004 grm. of NaHO. The acid solution is added 

 from a burette to 50 or 100 c.c. of the serum or blood, a drop of 

 the mixture being placed from time to time upon the slab coloured 

 with litmus ; the addition of acid is continued until the reaction is 

 faintly acid. The alkalinity of the blood may then be expressed as 

 corresponding to x milligrammes of sodium hydrate per 100 c.c. of 

 blood. 



Determination of the Water, Total Solids and Ash of the Blood. 



A Berlin porcelain crucible, furnished with a cover and having 

 a capacity of about 20 c.c., is dried and then accurately weighed. 

 From 2'5 to 5 grammes of defibrinated blood are carefully weighed 

 out in the crucible, which is then placed in a hot- water oven 

 heated to 100 C. (Fig. 30), until an apparently dry residue is left ; 

 the crucible is then heated in a hot-air oven furnished with a 

 regulator (Fig. 31), and kept at a temperature of 110 C. After 

 some time the crucible is transferred to an exsiccator (Fig. 32 or 

 33), where it is allowed to remain for a few minutes to cool, 



FIG. 30. HOT-WATER OVEN WITH ARRANGEMENT FOR KEEPING THE WATER AT A CONSTANT 



LEVEL. 



G. 12 



