GLUCOSE TESTS. 15 



28. Show that a glucose solution will reduce copper 

 acetate acidified with acetic acid 1 when heated for some 

 time in a water-bath. This is Barfoed's test. Observe the 

 difference between glucose and lactose with this test. 



29. Prove that when heated alone in water cupric 

 hydrate gives the black cupric oxid and not the red cuprous 

 oxid; also that with an excess of the copper solution the 

 black may hide the red oxid if only a small amount of 

 sugar is present. 



30. Show that glucose will also reduce the sub- 

 nitrate, or basic nitrate, of bismuth if its solution is made 

 alkaline by sodium hydrate or carbonate and boiled with 

 the bismuth compound. The bismuth oxid which is formed' 

 is a black powder, but if mixed with much of the unre- 

 duced bismuth subnitrate it may appear gray. This is 

 Boettger's test. The bismuth subnitrate, like cupric hy- 

 drate, is soluble in an alkaline solution of Eochelle salt, 

 and this solution when heated with glucose gives the black 

 oxid as a precipitate (Nylander's test). 



Heat a little of the bismuth subnitrate in a solution of 

 albumin which has been made strongly alkaline with sodium 

 hydrate, and notice that the sulphid of bismuth, which is formed, 

 has the same appearance as the black oxid which is produced by 

 the glucose; that is, albumin gives a similar result to that obtained 

 with grape-sugar. 



31. Dissolve in a small amount of water as much 

 phenyl-hydrazin hydrochlorid as can be taken up on the 

 point of a knife-blade and twice as much sodium acetate, 

 filtering if it is not clear. Add it to half a test-tubeful of 

 the sugar solution, place the tube in a beaker of boiling 



x The mixture of solution and sugar solution should contain 

 1.0 per cent, of cupric acetate and 1.0 to 1.25 per cent, of acetic acid. 



