302 SECRETION. 



To apply this test in ordinary qualitative analyses, heat 

 a small portion of the test-liquid to the boiling point in a 

 test-tube, and add the suspected fluid, drop by drop. If 

 sugar be present in even a moderate quantity, a dense yel- 

 lowish precipitate of the suboxide of copper will be produced 

 after adding a few drops; and if the liquid be added to 

 about the same volume as the test, and the mixture be again 

 raised to the boiling point, without producing any deposit, 

 it is certain that no sugar is present. The estimation of the 

 quantity of sugar in any liquid depends upon the fact that 

 two hundred grains of the test-liquid is decolorized by ex- 

 actly one grain of glucose. To apply this test, measure off 

 in a glass, specially graduated for the purpose, two hundred 

 grains of the solution ; put this into a flask, with about twice 

 its volume of distilled water, and boil ; when boiling, add 

 the suspected solution, little by little, from a burette gradu- 

 ated in grains (raising the mixture to the boiling point each 

 time and afterward allowing the precipitate to subside), until 

 the blue color is completely discharged ; by then reading off 

 the number of grains of the saccharine solution that has been 

 added, the proportion of sugar may be readily calculated. 

 If the solution be suspected to contain a considerable quan- 

 tity of sugar, the estimate may be more accurately made by 

 diluting it to a known degree, say with nine parts of water, 

 and adding this diluted mixture to the test-liquid. 1 



Bernard, in his quantitative examinations, employed a 

 test-liquid known as Barreswil's solution, but the process is 

 essentially the same as the one we have just described. One 

 advantage of boiling the standard liquid before applying the 



required. The original formula, given by Roberts, reduced to English grains, 



is as follows : 



Sulphate of copper, 90i grains ; 



Neutral tartrate of potash, 364 grains ; 



Solution of caustic soda, sp. gr. 112, four fluidounces. 



Add water to make exactly six fluidounces. 



(ROBERTS, A Practical Treat^e on Urinary and Renal Diseases, Philadelphia, 

 1866, p. 147.) 



1 ROBERTS, op. cit., p. 147. 



