206 DR. ROBERTS ON THE ESTIMATION 



very small. Two drachms shaken up with 4 oz. of water, 

 and left in a warm place for thirty- six hours, only increased 

 the density of the water by 0*3°. In the above experi- 

 ments a piece of yeast about the size of a large filbert or 

 small walnut was employed to ferment four ounces of 

 urine, a little more or a little less making scarcely a 

 sensible difference in the results. 



The fermented urine continues somewhat turbid for a 

 day or two after fermentation is completed, and the degree 

 of this turbidity has an appreciable though slight effect on 

 the density. In the experiments detailed in this paper the 

 second density was taken about twenty- four hours after 

 the addition of yeast, and before the urine had completely 

 cleared. It was found in four trials that if the urine was 

 allowed to rest twelve hours longer the density fell by 0"2° 

 or 0'3''. It is desirable, therefore, where a series of expe- 

 riments is made, and scrupulous accuracy and uniformity 

 are required, always to take the second density at about 

 the same period after fermentation has ceased. 



The method here proposed for determining sugar is not 

 put forward in rivalry with the accurate and elegant volu- 

 metrical process now usually employed by chemists ; but 

 it is believed that it will be of great service to the medical 

 practitioner, who is unaccustomed to delicate chemical 

 manipulations. Any one who has had much practice in 

 the volumetrical method knows that great nicety and con- 

 siderable experience are requisite to insure trustworthy 

 results. Fehling's test solution also is liable to speedy 

 deterioration unless hermetically sealed from the air. This 

 arises from the conversion of a portion of the tartaric acid 

 of the test into racemic acid, which, equally with sugar, 

 has a reducing power on the oxide of copper, and when 

 present of course vitiates the results. For these reasons 

 it may be surely predicted that the volumetrical method 

 can never come into general use at the bed-side. 



