212 THE INCOME OF ENERGY 



the aqueous extract of lipase to each. Boil tube 

 B. Place both tubes at 40 C. for fifteen min- 

 utes. Kemove them from the bath and plunge 

 them into ice-water (to check further ferment 

 action). Titrate with ^ KOH, using neutral lit- 

 mus as the indicator. 1 The initial acidity of the 



1 A normal solution contains in each litre one equivalent 

 weight of the active substance, i. e. that mass of the active sub. 

 stance which is equivalent to the atomic weight of a univalent 

 element in the reaction for which the normal solution is to be 

 employed. Equal volumes of different normal solutions are 

 equivalent to each other. Thus, 1 c.c. normal alkali solution 

 requires for neutralization exactly 1 c.c. normal acid, no matter 

 what acid is employed to make the normal solution. 



Preparation of Normal Potassium Solution. The content of 

 KOH in 1 litre is 56.16 grams. Dissolve 60 gms. purest com- 

 mercial KOH (which always contains considerable water) in a 

 graduated cylinder in about 950 c.c. water. Determine the 

 true content of KOH by titration with a normal oxalic acid 

 solution (prepared by dissolving its equivalent weight 63 gms. 

 in 1 litre water) as follows. Thoroughly stir the potassium hy- 

 droxide solution, fill a burette with a portion of the well-mixed 

 solution. Place 10 c.c. normal oxalic acid solution in a beaker 

 and add a few drops of solution of rosolic acid as indicator. 

 Add the alkali from the burette cautiously until the end point 

 of the reaction is reached, i. e. until the indicator gives a red 

 color which does not quickly disappear. As 10 c.c. of acid solu- 

 tion should exactly neutralize 10 c.c. of alkali solution, pro- 

 vided both were normal, it follows that the quantity of KOH 

 solution necessary to neutralize is to 10 c.c. as the total quantity 

 of the original KOH solution is to x. x will be the number of 

 cubic centimetres to which the KOH solution must be diluted 

 in order to make it normal. A portion of the normal solution 

 should then be diluted 1:20, and preserved in an air-tight 



