LIVING SUBSTANCE 



111 



liable of these reduction- tests are Trommer's test and Bottger's 

 test. They may be performed very simply in a test-tube. The 

 former consists in the reduction of cupric hydroxide to cuprous 

 oxide by an alkaline solution of grape-sugar. If a few drops of a 

 very dilute solution of cupric sulphate be added to a sugar solution, 

 made alkaline by caustic potash or soda, until a blue flocculent pre- 

 cipitate of cupric hydroxide appears, on boiling the latter is reduced 

 to red cuprous oxide or yellow cuprous hydroxide. In Bottger's 

 test a few drops of a solution of basic nitrate of bismuth is added 

 to the alkaline solution of grape-sugar ; the former is then reduced 

 to black metallic bismuth. A further very characteristic property 

 of the monosaccharids is their power of fermentation. They 

 become decomposed by the action of yeast-cells (Saccharomyces) 

 into alcohol and carbonic acid 



C 6 H 12 6 = 2C 2 H 5 OH + 2C0 2 . 



Such an experiment can be carried on best in a fermentation - 

 glass (Fig. 39), by introducing into it a solution of grape-sugar 



FIG. 39. Fermentation-tube a, newly filled ; b, with carbonic acid developing. At the top of 

 the straight limb a quantity of carbonic acid has already accumulated. 



mixed with fresh yeast, so that the liquid fills completely the long 

 closed limb of the glass. At a temperature of c. 30 40 C. there 

 appears a fairly energetic cleavage of the grape-sugar, small 

 bubbles of carbonic acid rising continually as in a glass of cham- 

 pagne, and accumulating at the upper end. The more carbonic 

 acid accumulates above, the more the liquid is forced out of the 

 long limb into the spherical part of the vessel, until finally the 

 former may be entirely filled with the gas. The presence of alco- 

 hol may be recognized at once by the odour of the liquid. One 

 more characteristic of the monosaccharids may be mentioned, 



