CH. VIII. 



ACHROMIC POINT METHOD. 



to achroo-dextrin and maltose, is known as the achromic point. 

 The time that is taken to reach this point (" chromic period ") is a 

 measure of the activity of the ferment. 



If the chromic period is 

 less than 4 minutes, dilute the 

 enzyme with one or more 

 volumes of distilled water and 

 repeat the experiment. A ' 



NOTES. i. The buffer solu- 

 tion is added to maintain the 

 optimum concentration of hydro- 

 gen ions. It is prepared by treating 

 50 cc. of 0-2 M. acid potassium 

 phosphate with 21 cc. of 0-2 N. 

 soda and adding distilled water to 

 make a total volume of 200 cc. 

 (See p. 27.) 



2. The reason for the ad- 

 dition of the sodium chloride is 

 explained in the text on p. 188. 



3. Starch paste can be used 

 instead of soluble starch, but it is 

 difficult to measure accurately by 

 means of a pipette, owing to its 

 viscidity. 



4. The use of the author's 

 " Distributor " (fig. 29) for auto- 

 matically delivering a given volume 

 of fluid is convenient for measuring 

 about 3 cc. of water into each tube. 

 Distilled water must be used, owing 

 to the action of tap water on 

 iodine. The iodine should not 

 be added until just before the 

 addition of the digesting mixture. 



238. Repeat the above 

 experiment, substituting 2 cc. 

 of distilled water for the 2 cc. 

 period is much prolonged. 



Fig. 29. Cole's "Distributor" for the 

 automatic delivery of a given vol- 

 ume of fluid. 



The fluid is placed in the beaker 

 and the air is driven out of the apparatus 

 by repeatedly compressing the rubber 

 ball. On firmly pressing down the 

 hinged board a given volume of fluid 

 is driven out of the apparatus. The 

 volume delivered can be varied by ad- 

 justing the screw C. The rubber tubing 

 should be thick pressure tubing and as 

 short as possible. The wooden base 

 should be screwed down. 



of sodium chloride. The chromic 



239. Determine the effect of dilution of the enzyme on the 

 chromic period. It will be found that the chromic period lengthens 

 out unduly as the ferment is diluted ; that is, the period is more 

 than trebled by a three- times dilution. 



