METABOLIC PROCESSES IN THE PLANT. 



283 



Fehling's solution. The fermented fluid is in every case to be 

 heated for a considerable time in a state of dilution before the 

 sugar determinations are made, in order to drive off the alcohol. 



Quantitative determinations of alcohol are made as follows : 

 Jot) c.c. of the fermented fluid, without being filtered, is distilled 

 in a flask of 400 c.c. capacity. To prevent the fluid from frothing 

 up, we put into it a fragment of paraffin. The flask in which the 

 distillate is collected must be closed almost air-tight, so as to pre- 

 vent loss of alcohol. During the distillation, the receiver must be 

 kept cool by means of a stream of cold water. When we have 

 obtained about 100 c.c. of distillate, we determine its specific 

 gravity. From this, by means of suitable tables (see Konig, 

 Untersuchuug la?idwirthschaftlich und gewerblich wichtiger Stoffe, 

 Tabelle 15), the quantity of alcohol con- 

 tained in 100 c.c. of the distillate can be 

 directly deduced in percentage by weight 

 or volume. The number found must be 

 divided by 2, since the distillate contains 

 the whole of the alcohol of the original 

 200 c.c. of fermented fluid. 



If it is required to lead gases (air, 

 Hydrogen) through the fermenting food 

 solutions, we may use the apparatus repre- 

 sented in Fig. 104. The funnel-shaped 

 portion, J, which receives the food solu- 

 tion, is continuous with the glass tube, J?, 

 on which is blown a bulb. The rubber 

 stopper, K, receives the thermometer, T, 

 and the gas exit tube, G. Through B 

 gas is introduced into the fluid, through 

 which it streams from below upwards. 

 The portion A of the apparatus has a 

 capacity of about 250 c.c. In order not to 

 lose the alcohol carried over with the gas, 

 '/ is connected with a condensing ap- 

 paratus. This consists of a small flask, which can be closed by 

 nu'uns of a two-holed cork. Into one hole passes a tube to carry 

 off the gas, while the other receives the tube bringing the gas, the 

 portion of this within the flask being in the form of a worm. 

 The lower end of the worm dips into some water contained in the 

 flask. The condensing apparatus is placed in a large glass con- 



FIG. 101. Apparatus for 

 investigating fermentation. 



