CHEMIC COMPOSITION OF THE HUMAN BODY. 27 



Fehlings Test Solution. This is a solution of cupric hydroxid 

 made alkaline by an excess, of sodium or potassium hydroxid with 

 the addition of sodium and potassium tartrate. It is made by 

 dissolving cupric sulphate 34.64 grams, potassium hydroxid 125 

 grams, sodium and potassium tartrate 173 grams, in distilled water 

 sufficient to make one liter. 



The reaction is expressed by the following equation: 



CuS0 4 + 2 KOH = Cu(OH) 2 + K 2 SO 4 . 



The object of .the sodium and potassium tartrate is to hold the 

 cupric hydroxid in solution. 



For qualitative analysis it is only necessary to boil a few cubic 

 centimeters of this solution in a test-tube; then add the suspected 

 solution and again heat to the boiling-point. If sugar be present, 

 the cupric hydroxid is reduced to the condition of a cuprous oxid, 

 which shows itself as a red or orange-yellow precipitate. The color 

 of the precipitate depends on the relative excess of either copper or 

 sugar, being red with the former, orange or yellow with the latter. 

 The delicacy of this test is shown by the fact that a few minims of 

 this solution will detect in i c.c. of water the -^ of a milligram of 

 sugar. 



For quantitative analysis, 10 c.c. of Fehling's solution, diluted 

 with 40 c.c. of water, are heated in a porcelain capsule, to which 

 the suspected solution is cautiously added from a buret until the blue 

 color entirely disappears. The strength of this solution is such that 

 i c.c. is decolorized by 5 milligrams of sugar (dextrose), from which 

 the percentage of sugar in any solution can be determined. 



All the sugars, with the exception of chemically pure saccharose, 

 may be tested for with this solution. 



The Fermentation Test. All the sugars with the exception of 

 lactose undergo reduction to simpler compounds, mainly alcohol and 

 carbon dioxid, under the action of the yeast plant, Saccharomyces 

 cerevisicB. The change with dextrose is expressed in the following 

 equation : 



C 6 H 12 O 6 = 2C 2 H 6 O + 2CO 2 . 



Dextrose = Alcohol + Carbon Dioxid. 



About 95 per cent, of the dextrose is so changed, the remaining 

 5 per cent, yielding secondary products succinic acid, glycerin, etc. 

 As a means of testing any solution for the presence of sugar this 

 method may be adopted. It is generally very satisfactory. From 

 the quantity of carbon dioxid and alcohol thus produced the quantity 

 of sugar in the solution may be determined. 



Levulose, or fruit-sugar, is found in association with dextrose 

 as a constituent of many fruits. It is sweeter than dextrose and 

 more soluble in both water and dilute alcohol. From alcoholic 



