CHAP. IV.] THE BLOOD. METHODS OF RESEARCH. 187 



the amount of iron determined with the aid of a standard solution of 

 potassium permanganate. By multiplying the amount of metallic 

 iron in 100 parts of blood by 100 and dividing by 0'43, we obtain the 

 percentage of haemoglobin. 



For the details of the method of determining the iron volumetri- 

 cally we refer the reader to any systematic work on Quantitative 

 Analysis. 



Determination of Cholesterin, Lecithin, and Fats in Blood (Hoppe- 



Seyler). 



20 to 50 c.c. of blood are treated with 3 or 4 times their volume 

 of absolute alcohol, set aside for a few hours, and then filtered. 

 The insoluble matter is washed, first with pure alcohol and then with 

 alcohol holding ether in solution. 



The mixed alcoholic and ethereal solutions are evaporated to 

 dryness on the water-bath. The residue is dissolved in ether, filtered, 

 evaporated to dryness, and weighed. 



In this way is obtained the combined weight of the cholesterin. 

 lecithin and neutral fats. 



The residue, after being weighed, is then treated with alcohol, 

 and a little alcoholic solution of caustic potash added, and heated, in 

 a silver dish, for some hours in the water-bath, until the whole of the 

 alcohol is expelled. The residue contains cholesterin, soaps, glycerin, 

 caustic potash and products of the decomposition of lecithin, viz. 

 glycerin-phosphoric acid, neurin, &c. 



The residue is then mixed with water and agitated repeatedly 

 with ether. The ethereal solution is evaporated to dryness, and 

 dissolved in absolute ether, which dissolves the cholesterin alone, 

 leaving undissolved traces of soaps, which were mixed with it. The 

 ethereal solution is evaporated at a low temperature, then dried below 

 80 C. and weighed. 



The watery solution, from which the cholesterin has been removed 

 by ether, is evaporated to dryness in a silver dish and fused with 

 sodium hydrate and pure nitre. The fused mass is dissolved in water, 

 and treated with an excess of nitric acid. 



The phosphoric acid is then precipitated by means of an acid 

 solution of ammonium molybdate. The precipitate, which has 

 separated after 12 hours, is dissolved in ammonia and the solution 

 precipitated by magnesia mixture, the precipitate being washed, 

 dried, ignited and weighed as magnesium pyrophosphate. 



100 parts of magnesium pyrophosphate correspond to 764 '5 parts 

 of lecithin. 



For full directions how to estimate the phosphoric acid in the 

 above case, the reader is referred to works on quantitative analysis. 



