SUGAR. 63 



mixture then rendered distinctly alkaline by the addition of potassium 

 hydrate. The whole solution then takes a deep-blue color. On boiling 

 the mixture, if sugar be present, the copper suboxide is thrown down as 

 an opaque red, j^ellow, or orange-colored deposit ; otherwise no change 

 of color takes place. In this reaction the sugar, which is oxidized at a 

 high temperature under the influence of the alkali, takes a portion of 

 its oxygen from the copper in the copper salt, and thus reduces it to 

 the form of an insoluble suboxide. 



Some precautions are necessary in the use of this test. As a general 

 rule, only a small quantity of the copper sulphate should be added to 

 the liquid under examination, just sufficient to give to the whole a dis- 

 tinct blue tinge after the addition of the alkali. If the copper salt be 

 used in excess, the sugar in solution may not be sufficient to reduce the 

 whole of it ; and that which remains as a blue sulphate may mask the 

 yellow color of that which is thrown down as a deposit. This diffi- 

 culty may be removed by due care in the proportion of the ingre- 

 dients. 



Furthermore, there are some albuminous substances which have the 

 power of interfering with Trommer's test, and prevent the reduction of 

 the copper even when sugar is present. Certain animal matters, to be 

 more particularly described hereafter, which are liable to be held in solu- 

 tion in the gastric juice and in the blood, have this effect. 



The ordinary ingredients of the urine also interfere with the complete 

 reaction of Trommer's test, by holding the copper oxide in solution, so 

 that no precipitate takes place when glucose is present, although the 

 liquid turns yellow on boiling. A very large proportion of glucose may 

 be added to fresh urine without giving rise to a pulverulent precipitate 

 on the application of Trommer's test; notwithstanding that, if dis- 

 solved in water, it will react in the proportion of one part in 10,000. 

 That the interference of urine with Trommer's test depends on its 

 retaining in solution the reduced copper oxide, and not upon its pre- 

 venting deoxidation, is indicated by the fact that the color of the 

 mixture changes, as usual, from blue to yellow although no precipitate 

 takes place ; and also by the experiments of Dr. Fowler, 1 who has shown 

 that if the precipitate resulting from Trommer's test with a watery solu- 

 tion of glucose be added to boiling urine, it is at once redissolved. The 

 same observer has devised a method of applying the test successfully 

 notwithstanding the interference of the urine. A certain quantity of 

 urine can, of course, only dissolve a certain amount of copper oxide ; 

 and if the copper sulphate solution be added to a specimen of saccharine 

 urine in large proportion, the excess will be precipitated and show itself 

 as a deposit. A copper sulphate solution, made in the proportion of 1 

 part copper sulphate to T.5 parts of water, and added to saccharine urine 

 to the amount of one-half or one-third its bulk will generally be suffi- 

 cient to produce a satisfactory reaction. 



1 New York Medical Journal, June, 1874, p. 632. 



