BASIC AND ACID PROPERTIES OF PROTEINS 25 



originally consisted chiefly of sulphate, is dissolved in sodium chloride 

 solution containing I c.c. of decinormal hydrochloric acid for each 

 gramme of dissolved edestin and the resulting solution is dialysed, the 

 edestin separates in crystals which on neutralisation yield chiefly 

 potassium chloride as shown by the following figures : 



Per cent. 



Potassium carbonate 2*01 



Potassium sulphate 16*31 



Potassium chloride 73*65 



Undetermined and loss 8*03 



100*00 



Here over 82 per cent, of the potassium is chloride and less than 

 1 6 per cent, is sulphate, the proportions being almost exactly the re- 

 verse of those in the preparation of the identical protein substance 

 previously precipitated from a solution of a sulphate. 



Further, it is probable, in view of the recovery of most of the 

 potassium, used for neutralising, in salts described in the experiments 

 reported above, that such titrations are very nearly true measures of 

 the absolute amount of combined acid. If such be the case edestin, 

 with respect to its first basic group, cannot be a very weak base. 



The amount of acid which is thus combined with edestin corre- 

 sponds, in the very large number of different preparations which have 

 been examined, to from ro c.c. to 1*4 c.c. of decinormal alkali per 

 gramme. Variations in the quantity of this combined acid can be 

 readily determined by titration with potassium hydrate, using 

 phenolphthalein as an indicator, for the end reaction is sharp and 

 easily recognised. Owing to the fact that edestin can be obtained in 

 the form of extremely minute crystals which show no tendency to 

 adhere in lumps, it is possible to suspend it in an exceedingly finely 

 divided state in distilled water and to determine the quantity of com- 

 bined acid, even in the solid state, by titration with potassium hydrate. 

 The result thus obtained is the same as that found by dissolving the 

 edestin in neutral sodium chloride solution, though the end reaction 

 takes place a little more slowly under the first-named conditions. 

 The whole of the combined acid can therefore be determined by 

 neutralising the crystals when suspended in pure water, although 

 these do not dissolve during the process. 



That this acidity can be determined with apparent ease is due to 

 the fact that edestin has such feeble acid properties that they do not 

 interfere with the use of phenolphthalein as an indicator, and also to 

 the fact that the acid which is thus determined by titration is almost 

 wholly strong mineral acid. Toward indicators less sensitive than 



