CHAP. IV.] THE BLOOD. METHODS OF RESEARCH. 179 



The crucible is now uncovered and placed, upon a triangle, over a 

 Bunsen flame, so as to char its contents. At first the application of 

 heat is conducted with much caution, the flame being at a con- 

 siderable distance from the bottom of the crucible ; if this precaution 

 be not taken the contents are very apt to froth up and to be partially 

 lost. Soon, however, the heat may be increased by placing the 

 crucible so that it is surrounded by the flame, and it will prove 

 advantageous to place the crucible in the tilted position indicated 



FIG. 34. ARRANGEMENT EMPLOYED IN DETERMINING THE AMOUNT OF ASH IN BLOOD. 



in the annexed figure (Fig. 34). If conducted in a porcelain crucible 

 the process is a very slow one. When the carbon has been entirely 

 burnt away, the ash presenting a reddish-white colour without 

 intermixture of black, the crucible is cooled in the exsiccator and 

 weighed. This method of determining the ash does not possess 

 great value, for the reasons already referred to at considerable length 

 (see p. 66). The following process should be followed when it is 

 desired to attain as great accuracy as is compatible with the 

 method of incineration. 



Rose's me- The dried residue of the blood is heated over a 



Bunsen flame until it is thoroughly carbonized ; care is 

 however taken that the crucible does not become even faintly red. 

 Having been allowed to cool, the contents of the crucible are treated 

 with boiling distilled water and heated for some time ; the aqueous 

 solution is filtered through a small filter of Swedish filter paper, 

 and kept. The carbonized residue is treated again and again with 

 hot distilled water, to make sure of dissolving all soluble salts. 



12-2 



