ANIMAL SUGARS. 67 



charine taste, and dissolve in about 37 parts of cold water, 



and slightly in alcohol. The formula for this combination is 



C,„ H,^ O,^, 2H0 + C„^ H,.^ O,.^, NaCl. 



Tests for Diabetic Sugars a. HixnefelcVs test. Place 4 oz. 

 of the suspected urine in a glass exposed to the sun's rays, 

 and add about 6 drops of a tolerably strong solution of chromic 

 acid. In a few minutes if sugar be present, the mixture, 

 previously orange red, becomes brownish, and soon after as- 

 sumes a bistre-brown coloiu'. These changes take place much 

 more quickly if the mixture of imne and chromic acid be 

 gently warmed before exposure to light. 



This test depends for its action upon the deoxidizing power 

 of the sugar, by which the chromic acid is reduced to oxide of 

 chromium ; for, after ■« arming the mixture, the addition of a 

 few drops of liquor jwtassa produces a copious deposit of the 

 green oxide. 



There is an important objection to this test which renders all 

 its indications liable to serious fallacy, depending upon the fact, 

 that all urine containing a normal proportion of colouring 

 matter deoxidizes chromic acid ; and consequently urine, whether 

 saccharine or not, will partially convert this acid into the oxide. 

 This change certainly does not occur so readily in non-saccha- 

 rine urine as in a diabetic state of that fluid, but still is suffi- 

 ciently marked to prevent Hlinefeld's test being regarded in 

 any other light than a fallacious one. 



b. Runge's test. Allow a thin layer of the suspected urine to 

 evaporate on a white surface, as the bottom of a white plate, 

 and, whilst warm, drop upon the surface a few di'ops of sulphuric 

 acid, pre\dously diluted with 6 parts of water. With healthy 

 urine, the part touched with the acid becomes merely of a pale 

 orange colour, from the action of the latter upon the colouring 

 matter of the urine ; whilst if sugar be present the spot becomes 

 deep brown, and soon black, from the decomposition of sugar 

 by the acid, and consequent deposition of carbon. This test is 

 stated to be so delicate, that 1 part of sugar dissolved in 1000 



' The following observations are principally taken from an excellent paper, by Dr. 

 G. Bird, on the detection of a diabetic state of the urine, in the London Medical 

 Gazette for 1843. ^ye have omitted to notice the test afforded by the rotatory 

 power of a solution of sugar on a ray of polarized light, as it has been shown by 

 Dr. Leeson to afford very fallacious results. Memoirs of the Chemical Society, Part 7. 



