286 YEAST. 



Dissolve the powdered mixture in water, as required for use 

 in the proportion of 2 grams to 100 c.c. of water, and add 

 16 grams of cane sugar. 



411. Alcoholic Fermentation. About two- thirds fill 

 a fairly large flask with Pasteur solution and add some 

 Yeast that has been stirred up with water to form a 

 paste. 



(a) Plug the neck of the flask lightly with cotton- wool, 

 and set it in a warm place ; note that the liquid becomes 

 cloudy and frothy, bubbles are given off, and the liquid 

 after a time smells of alcohol. 



(6) Now fit the flask with a bored cork through which 

 passes a tube bent like a J, with the longer arm dipping 

 into a vessel of baryta- water (or lime-water) ; note the evo- 

 lution of bubbles of carbon dioxide. 



(c) Now replace the J-tube in the cork of the flask by a 

 straight narrow tube about 30 inches long, not allowing its 

 lower end to dip into the liquid; heat the flask over a 

 Bunsen or spirit lamp, fixing it in a retort-stand, and note 

 that after a time the alcohol- vapour given off can be 

 lighted at the upper end of the tube, burning with the 

 characteristic blue flame seen in a spirit lamp. 



(d) Repeat the preceding experiments with a flask of 

 Yeast and Pasteur solution which has been boiled for five 

 minutes; no fermentation takes place, and no alcohol or 

 carbon dioxide are formed, because the Yeast cells have 

 been killed. 



(e) G-et ready a series of six jars or tumblers, fitted with 

 covers or corks. In A put water ; in all the others, 

 Pasteur solution; add to each a tablespoonful of thin 

 Yeast paste (or simply a bit of dry Yeast). Place B in 

 darkness, keep the others in the light in the ordinary way. 

 Place in a temperature of C. or very little above it ; 

 D at the ordinary room temperature ; E at a high tempera- 

 ture, about 35 C. ; and boil the Yeast and the Pasteur 

 solution for F in a flask for five minutes before pouring it 

 into the jar. 



