212 STANDARDIZATION OF PEPTONES 



differently observed, it has to be determined how 

 great the limits of error are, on the average. It has 

 been found, that most observers are capable of read- 

 ing with accuracy to o'O2 of a degree. In order to 

 attain greater certainty, we shall consider even a 

 difference of 0*04 of a degree as the limit of error. 

 Only with a change of rotation of 0*05 of a degree can 

 decomposition be assumed to have taken place. The 

 limit can thus be fixed without any danger, because, 

 when an hydrolysis of the peptone does take place, 

 the alteration of rotation is certainly more than 0*04 

 of a degree. 



This method, as such, presents hardly any sources 

 of error. At most, errors may be occasionally pro- 

 duced through turbidity, precipitates, and the like, 

 Fortunately, however, in such cases, which actually 

 very seldom happen with proper working, the reading 

 of the rotation is impossible, and so this source of 

 error disappears of itself. Of course, we should get 

 no result if we were to try to polarize a cloudy solution. 



A very important source of error would arise, if the 

 range of rotation of the cold solution were taken for 

 the initial value. The readings must be taken from 

 the moment the contents of the tubes reach a tem- 

 perature of 37 C. It is best to take the reading at 

 the end of one hour, and take another at the end 

 of the second hour. Values obtained in such a 

 manner should, in general, not be too distant one 



