BLOOD. 235 



Simplification of the Method of Preparing the Ash. The 

 above method of preparing the ash may be simplified by 

 extracting the carbon with water instead of with hydro- 

 chloric acid. The aqueous extract may be disregarded, as 

 it contains no iron/ and the ash remaining may be directly 

 dissolved in the sulphuric acid of the concentration given 

 above. The complete oxidation of the ash takes place with 

 somewhat more difficulty. 



The preparation of the ash may also be accomplished 

 more conveniently by not evaporating the blood directly 

 and then igniting, but by treating it first according to Kjel- 

 dahl. Fifteen to twenty cubic centimeters of blood are 

 heated with 20 to 30 cc. of sulphuric acid and some mercuric 

 oxide or mercuric chloride solution. Ultimately some more 

 hot sulphuric acid is added and the heating is continued until 

 the solution has become colorless. When cold this is placed 

 in a platinum dish, the flask rinsed with a small quantity of 

 water, the excess of sulphuric acid driven off on the sand- 

 bath, and then ignited completely. Although this method 

 may perhaps appear more roundabout, yet it is really more 

 convenient. The method of previously heating with sul- 

 phuric acid in a Kjeldahl flask may also be advantageously 

 used for the quantitative determination of many other ash 

 constituents, as well as for the detection of metallic poisons. 



The destruction of the organic matter may be more 

 readily accomplished according to the method of A. Neumann 

 by using with the sulphuric acid the same amount of ammo- 

 nium nitrate. 



Gravimetric Determination of the Iron. If only single 

 determinations of iron are to be made, instead of a long 

 series, the gravimetric determination as ferric phosphate, 

 FeP0 4 , is more convenient. For this purpose add to the 



1 It may, however, contain iron if the extract is highly colored. 



