LABORATORY STUDIES 103 



test tube, when they will rise to its closed end. Respiration 



in its first (anaerobic) stage will go on and gas will 



be formed, oftentimes driving nearly all the mercury I 



out of the tube. Introduce a strong KOH solution J1L 



or a piece of stick KOH and a little water under 



the edge of the test tube and the gas will all be ait 



absorbed, showing that it is C0 2 that was produced. ^erT 



(q) Yeast plants ordinarily carry on only this first m eYt 

 stage of respiration (called fermentation in this case). ^' 

 To potato water (made by grating up a potato and boiling it in 

 a little water and expressing the latter) add about 5 per cent, 

 glucose. Place in a flask with a cork and a glass tube bent so as 

 to lead the gas produced under water. Break up part of a cake 

 of compressed yeast in a little water and add it to the solution in 

 the flask and insert the cork and glass tube. In a short time 

 gas will begin to escape in bubbles from the end of the tube. 

 Collect some in a test tube and test in various ways such as for 

 inflammability, absorption by KOH, etc. It will be found to 

 be C0 2 . Note what large amounts are produced. After the 

 evolution of gas has ceased the proper chemical tests will show 

 the presence of alcohol in the liquid. Distill the latter and 

 collect the first part that comes over. Add to it some strong 

 KOH solution and some flakes of iodine, and heat. If alcohol is 

 present a strong odor of iodoform will be produced and if much 

 is present this will show as a yellow precipitate. 



(r) The liberation of heat during respiration can be demon- 

 strated by placing a quantity of soaked peas or a number of 

 mushrooms just expanding in a flask with an accurate chemical 

 thermometer bulb in their midst and placing this flask in a 

 mass of cotton in another vessel and covering all with several 

 layers of cloth, leaving only the thermometer tube exposed. 

 Often the temperature within the flask will rise 3 or 4 degrees 

 or more above that of the surrounding air. Of course this 

 experiment must be carried on in a room where the temperature 

 is fairly constant. If a Dewar bulb or a Thermos bottle is used, 

 these being double walled with a vacuum between so that the 

 loss of heat is very small, the difference of temperature is 

 much more marked. 



(s) Without special thermostats where temperatures can be 

 controlled exactly, satisfactory experiments as to the cardinal 

 points of temperature cannot be made. However, it will be 



