CH. X] AMIDES. 239 



from a knowledge of the processes described for proteids. 

 For the colorimetric method it is necessary to make 

 standard solutions of pure peptone : any good commercial 

 peptone may be used for this purpose, but it should be 

 carefully dried before weighing out the quantities needed 

 for the standard solutions. 



Estimation of Amides. 



Amides are estimated in a solution from which proteids 

 and peptones and albumoses have been removed by the 

 processes described for qualitative testing. The separa- 

 tion of amides, if several are present, is a matter of much 

 difficulty; it is generally sufficient to estimate the total 

 ' amides ' together and calculate the result as asparagin ; 

 results obtained in this way should be stated as ' amides 

 calculated as asparagin.' 



Sachsse's method. 



This method (decomposing amides with potassium 

 nitrite and sulphuric acid, measuring the volume of 

 nitrogen evolved) gives very good results but is rather 

 difficult to manipulate and, unless great care is taken at 

 all stages of the operation, gives results seriously too high. 



For the details of Sachsse's method see Dragendorff, 

 § 241, p. 245. 



With asparagin the reaction is 



C4H8N A + 2HNO2 = CAOs + 4N + 2H,0. 



Therefore in this process 56 grs. nitrogen = 132 grs. 

 anhydrous asparagin. 



