164 BACTERIOLOGICAL CHEMISTRY LESSON 



Test the other tube with Fehling's solution after 

 twenty-four hours : marked reduction of copper. 



Boiling destroys the enzymes in solution. 



D. SEPARATION or ENZYMES. 



(a) Precipitation by alcohol (Barth). 



(1) Fresh yeast is dried at the ordinary temperature in 

 vacuo over sulphuric acid (a fairly large quantity of yeast 

 must be used). 



(2) Rub up the dried yeast into a fine powder. 



(3) Dry the powder in the hot-air chamber at 100 C. 

 for six hours. 



(4) Allow it to cool, and when it is quite cold add 

 distilled water, so as to convert it into a thin mess. 



(5) Let this suspension stand and settle at 40 C. for 

 twelve hours. 



(6) Decant the supernatant water, and filter it till it is 

 clear. 



(7) Pour the filtrate into five to six times its volume of 

 90 per cent spirit : a precipitate appears. 



(8) Allow the precipitate to settle, and filter at once. 



(9) Wash the residue on the filter-paper with absolute 

 alcohol. 



(10) Eemove the alcohol by means of pressure, and 

 shake the residue up with water. 



(11) Again filter, and precipitate the filtrate with 

 alcohol. 



