120 THE BLOOD. 



258. Test a parchment dialyzer or tubing to see that it has 

 no holes, then introduce defibrinated blood diluted with an equal 

 volume of water. Let it stand an hour or more in water. Notice 

 that the large haemoglobin molecules cannot pass out, but the 

 small molecules of chlorids do so, as is shown by adding silver 

 nitrate to the outer liquid. 



259. To a solution of blood in water add a small 

 crystal of potassium chlorate or potassium ferricyanid. 

 Methsemoglobin is formed, the color of the solution chang- 

 ing from a red to a brown. Make it slightly alkaline and 

 it becomes red. Examine the spectrum of the alkaline so- 

 lution. It is much like that of oxyhaBmoglobin, though 

 the first band is broader and extends somewhat farther 

 toward the red. It is reduced to haemoglobin by ammo- 

 nium sulphid, like oxyha3moglobin. 



260. Large amounts of crystalline methaemoglobin can be 

 obtained by adding to a concentrated solution of oxyhaemoglobin 

 enough of a concentrated solution of potassium ferricyanid to give 

 it a deep-brown color. Crystallize, as in the case of oxyhaemo- 

 globin, by cooling to zero and adding one-fourth the volume of 

 cold alcohol. 



261. PREPARATION OF ELEMATOPORPHYRIN. Saturate 75 

 grammes of glacial acetic acid with hydrobromic acid at 10 and 

 add to it in a 300 cubic centimeter flask 5 grammes of dry hsemin 

 crystals. Heat thirty minutes on a water-bath until no more 

 hydrobromic acid fumes escape, then pour into a liter of water. 

 After standing several hours filter and to the red filtrate add 

 sodium hydrate till the liquid is neutral. The coloring matter is 

 precipitated and should be filtered off, washed, and drained upon 

 filter-paper. Digest the moist precipitate with dilute sodium 

 hydrate on the water-bath; filter off the hydrate of iron, which 

 separates, and allow the solution to stand until the sodium 

 compound of hsematoporphyrin has separated in crystalline 

 masses. Dissolve these in water and precipitate the coloring 

 matter by acidifying with acetic acid. Filter, wash with water, 

 and after stirring the precipitate up to a paste with a small 



