SULPHUR 159 



10. The Compounds of Proteins with Sulphur. Uhl (118) 

 has prepared sulphur compounds of the proteins by utilizing 

 the reaction: 



< H 



I X R + CS 2 = I R 



H C = S 



I 

 SH 



which occurs in alkaline solution. These compounds combine 

 with heavy metals; the salts thus formed contain a high pro- 

 portion of the heavy metal and are soluble in water. 



11. The Compounds of Proteins with Oxygen. The best 

 known compound of this type is that of oxygen with the coloring 

 matter of the blood, haemoglobin. This has been especially 

 studied by Hiifner (50) who employed the spectrophotometric 

 method of measurement, and found that at high pressures (by 

 interpolation) the amount of oxygen bound up by one gramme of 

 haemoglobin is 1.338 cc., reduced to standard temperature and 

 pressure. Carbon monoxide combines with haemoglobin in 

 equivalent proportions. Hiifner considered that the reaction 

 between haemoglobin and oxygen is a balanced reaction, namely, 

 Hb -j- 2 ?=* Hb0 2 . From this, if the concentration of reduced 

 haemoglobin be Cr and of oxyhaemoglobin C and that of oxygen 



where P is the partial pressure of oxygen and a t the absorption- 

 coefficient of the gas at temperature t it would follow that if K 

 is the velocity constant 



Co = Ka t 

 CrXP 760' 



the quantities on the right of this equation being constant at 

 constant temperatures, the relation between the oxygen tension 

 and the percentage of haemoglobin converted into oxyhaemoglobin 

 should be expressed by a rectangular hyperbola. Bohr (21), 

 however, found that the curve of dissociation of oxyhaemoglobin 

 is not a rectangular hyperbola, and he explains his results by 

 supposing that the haemoglobin, in the presence of oxygen, first 

 splits off a haematin-containing moiety and that this then sub- 



