SUGAR. 85 



of copper, even when present in large quantity. Maple sugar, also, 

 which resembles cane sugar in some other respects, reduces the 

 copper, in Trommer's test, but slowly and imperfectly. Beet-root 

 sugar, according to Bernard, presents the same peculiarity. If 

 these sugars, however, be boiled for two or three minutes with a 

 trace of sulphuric acid, they become converted into glucose, and 

 acquire the power of reducing the salts of copper. Milk sugar, 

 liver sugar, and sugar of honey, as well as grape sugar and glucose, 

 all act promptly and perfectly with Trommer's test in their natural 

 condition. 



Secondly, care must be taken to add to the suspected liquid only 

 a small quantity of sulphate of copper, just sufficient to give to the 

 whole a distinct blue tinge, after the addition of the alkali. If a 

 larger quantity of the copper salt be used, the sugar in solution 

 may not be sufficient to reduce the whole of it ; and that which 

 remains as a blue sulphate will mask the yellow color of the sub- 

 oxide thrown down as a deposit. By a little care, however, in 

 managing the test, this source of error may be readily avoided. 



Thirdly, there are some albuminous substances which have the 

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

 tion of the copper even when sugar is present. Certain animal 

 matters, to be more particularly described hereafter, which are 

 liable to be held in solution in the gastric juice, have this effect. 

 This source of error may be avoided, and the substances in ques- 

 tion eliminated when present, by treating the suspected fluid with 

 animal charcoal, or by evaporating and extracting it with alcohol 

 before the application of the test. 



A less convenient but somewhat more certain test for sugar is 

 that of fermentation. The saccharine fluid is mixed with a little 

 yeast, and kept at a temperature of 70 to 100 F. until the fer- 

 menting process is completed. By this process, as already men- 

 tioned, the sugar is converted into alcohol and carbonic acid. The 

 gas, which is given off in minute bubbles during fermentation, 

 should be collected and examined. The remaining fluid is purified 

 by distillation and also subjected to examination. If the gas be 

 found to be carbonic acid, and the remaining fluid contain alcohol, 

 there can be no doubt that sugar was present at the commencement 

 of the operation. 



The following list shows the percentage of sugar in various 

 articles of food. 1 



1 Pereira, op. cit., p. 5o. 



