STUDIES OF SPORE-PLANTS 273 



upright position, quickly remove the stopper and plunge a glowing 

 taper into the gas. Result ? (3) Instead of testing with flame, the 

 invisible gas may be poured into tube having lime-water. 



Experiment 6. (D) Effect of the gas on a flame. Take a pint 

 bottle or fruit-jar, pour in some molasses-solution, add yeast, cork 

 tightly, and allow fermentation to go on for several days. Then 

 remove cork and quickly insert a glowing taper. Result ? 



Experiment 7. (D) Alcohol produced by fermentation of sugar. 

 (1) Put a few drops of strong alcohol in a test-tube half full of water, 

 add a crystal of iodine, and heat over gas- or alcohol-lamp. Then 

 add strong solution of caustic potash, or baking soda, until the iodine 

 color fades. Notice the crystals and odor of iodoform, especially 

 after cooling. This is a test for alcohol. (2) Take some molasses- 

 solution in which yeast has been growing for several days, add 

 iodine, and test as above. From a large quantity of fermented 

 molasses some alcohol might be collected by distilling. 



Experiments. (D) Effect of dense sugar solution. (1) Place some 

 yeast in undiluted molasses, keep in a warm place, and compare with 

 results previously obtained with molasses-solution. Write your 

 conclusions concerning the fact that fruit "preserves" do not fer- 

 ment. (2) Take some "preserved" fruit long kept free from fer- 

 mentation, place in test-tube or bottle with distilled or boiled water, 

 add some yeast, keep in warm place. Results? Conclusions? 



Experiment 9. Bubbles formed by gas from fermentation. (D) 

 Place some yeast in molasses-solution in a test-tube, and pour on 

 the surface of the molasses a small quantity of flour paste. The 

 paste will form bubbles as the gas is evolved. 



Experiment 10. Yeast in bread-making. (Optional.) These 

 experiments may be prepared by some pupils at home and demon- 

 strated to the class with full explanations. Mix some actively 

 growing yeast with flour and water to make dough. Bake some 

 lumps of the dough at once and others after leaving in a warm place 

 until "rising" occurs. At the same time mix some baking powder 

 with flour and water, and bake some of the lumps of the dough. 

 Cut across the lumps, and compare the cut surfaces. What has 

 been the effect of the yeast? Of the baking powder? Compare 

 with the previous experiment with bubbles. 



Experiment 11. Wild yeasts. (D, optional.) (1) Crush some 

 fruit (apples or grapes), put the juice into a test-tube, plug with 

 cotton, and leave in a warm place. (2) Put some molasses-solution 

 into another tube, and leave exposed to the air in a warm place. 

 Does fermentation occur? Examine a drop of the fluid with the 



