INTRODUCTION 3 



are in many cases so unstable, that their solutions 

 do not permit a heating to 6o° C, that they are in 

 most cases rapidly destroyed by acids or bases, and 

 that if one tries to free them from accompanying 

 albuminous substances by precipitating these, 

 they are often carried down with the precipitate. 

 Common chemical methods are therefore of a 

 very limited value. On the other hand, physical 

 chemistry allows us to follow quantitatively the 

 influence of temperature and of foreign substances 

 upon these interesting organic products, which are 

 of the greatest importance in industry, in the 

 physiological processes of daily life, and in diseases 

 and their therapy. 



The quantitative relations between the properties 

 of these substances and their concentration, temper- 

 ature, and the concentration of substances exerting 

 an influence upon them are given by mathematical 

 formulae. These formulae give a concise descrip- 

 tion of the phenomenon investigated. From their 

 form it is in most cases possible to understand the 

 mode of action of the temperature, concentration, 

 and of foreign substances, which is the aim of our 

 investigations. A knowledge of the differences 

 between the magnitude of the observed quantities 

 and the corresponding calculated values is useful 

 in a twofold manner. On the one hand, it allows 

 us to determine the probable value of the experi- 

 mental errors and thereby to improve the methods 

 of investigation. Amongst different methods in 

 which the experimental conditions are changed we 



