PHYSIOLOGICAL CHEMISTRY 



tube connect this flask with a second flask containing a solution of barium 

 hydroxide protected from the air by a soda lime tube in the stopper (see Fig. 3). 



Place the flasks in a warm place and note the 

 passage of gas bubbles into the barium hydroxide 

 solution. As these gas bubbles (CO 2 ) enter, a 

 white precipitate of barium carbonate will form. 

 The glucose has been fermented according to the 

 following equation: 



FIG. 3. FERMENTATION 

 APPARATUS. 



FIG. 4. IODOFORM. (Autenrieth .) 



2<X> 2 



When the activity of the yeast has practically ceased decant the supernatant 

 fluid, return it to the cleaned flask, connect with a condenser and distil. Catch 

 the first portion of the distillate, which may be redistilled if its alcohol content 

 is low, and test for alcohol by one of the following re- 

 actions : 



(a) lodoform Test. Render 2-3 c.c. of the distillate 

 alkaline with potassium hydroxide solution and add a 

 few drops of iodine solution. Heat gently and note 

 the formation of iodoform crystals. Examine these 

 crystals under the microscope and compare them with 

 those hi Fig. 4. 



(b) Aldehyde Test. Place 5 c.c. of the distillate 

 in a test-tube, add a few drops of potassium dichro- 

 mate solution, K 2 Cr 2 O7, and render it acid with dilute 

 sulphuric acid. Boil the acid solution and note the 

 odor of aldehyde changing to that of acetic acid. 



8. Fermentation Test "Rub up" in a mortar 

 about 20 c.c. of the sugar solution with a small piece 

 of compressed yeast. Transfer the mixture to a sac- 

 charometer (shown in Fig. 5) and stand it aside in a 

 warm place for about twelve hours. If the sugar is 

 fermentable, alcoholic fermentation will occur and car- 

 bon dioxide will collect as a gas in the upper portion of 

 the tube. On the completion of fermentation introduce 

 a little potassium hydroxide solution into the graduated 



portion by means of a bent pipette, fill the bulb portion with water, place the 

 thumb tightly over the opening in the apparatus and invert the saccharometer. 



FIG. 5. EiNHORNj SAC- 

 CHAROMETER. 



