354 VEHICLES OF CHEMICAL CORRELATION 



globin has also been established by Barcroft, as the following data 

 reveal. The oxygen pressure was constantly maintained at 10 mm. Hg 



Percentage of hemoglobin converted into oxyhemoglobin. 

 At 16 24 32 38 49 



Observed 92- 71 37 18 6 



Calculated 90 71 41 22 6 



from which figures and the above equation it is easy to deduce that 

 "q" or the heat given out when one gram-molecule of hemoglobin 

 unites with oxygen, is 28,000 calories. Now the heat given out when 

 one gram of hemoglobin unites with oxygen is 1.85 calories. Hence 

 we have the simple ratios: 



weight in grams of Heat given out by one gram- 

 one gram-molecule molecule 28, 000 



Weight of one gram Heat given out by one gram 1.85 



whence the weight in grams of one gram-molecule of hemoglobin is 

 calculated to be 15,200, which estimate, when one recollects the number 

 and variety of measurements which enter into it, is in extraordinarily 

 good accord with the known molecular weight of hemoglobin, namely, 

 about 16,000. 



FIG. 20. Hemin crystals, magnified. (After Preyer.) 



By the action of acids, alkalies or heat in the presence of oxygen, 

 hemoglobin can readily be split up with the liberation of Hematin. 

 If this hydrolysis is accomplished in the presence of hydrochloric acid 

 the substance obtained is the hydrochloride of hematin or Hemin, 

 which may be readily recognized by its characteristic crystalline form 

 (see Fig. 20). 



Alkaline solutions of hematin show pronounced Dichroism, being 

 red in thick, and green in thin layers, while acid solutions of hematin 

 are brown. The solid substance forms glistening bluish-black amor- 

 phous masses. The hydrochloride, however, is brown. 



If hematin be dissolved in strong Sulphuric Acid, on diluting the 



