1402 FOODS AND FOOD ADULTERANTS. 



iodid solution. Sometimes, not often, the proteid matter will not sep- 

 arate. In this case follow Kfilz's method of nearly neutralizing with 

 potassium hydroxid and adding again hydrochloric acid, and the pre- 

 cipitate will usually flocculate. The proteid matter being now precip- 

 itated as completely as possible, the whole is transferred to a 500 cc 

 flask, made to the mark with water, well shaken, and an aliquot por- 

 tion (say 250 cc) filtered through a fluted filter. A drop or two of 

 phenolphthalein is now added and the solution titrated to exact neu- 

 trality with a concentrated solution of potassium hydroxid, noting the 

 amount used. If a slight amount of flaky-looking matter separates 

 at this point the liquid is again passed through a fluted filter, and such 

 a volume taken as will correspond to two-fifths of the original mate- 

 rial, of course taking into consideration the number of cubic centi- 

 meters of potassium hydroxid used to neutralize the hydrochloric 

 acid. Three or four drops of concentrated hydrochloric acid are now 

 added, and twice the volume of from 93 to 95 per cent alcohol. After 

 standing two or three hours the precipitated glycogen is filtered off 

 through a paper filter, washed with dilute alcohol (2 parts 95 per cent 

 alcohol and 1 part water), then with 95 per cent alcohol, then with 

 ether; dried at from 80 to 100, then at 115, and weighed in a weigh- 

 ing tube. The filter is then extracted thoroughly with boiling water, 

 dried again at 115, and again weighed in a weighing tube, the differ- 

 ence in weight representing glycogen. 



METHOD OF PFLUGER AND NERKING.* 



Fifty grams of finel} 7 macerated meat are digested on the water 

 bath with 200 cc of 2 per cent potassium hydroxid until solution is 

 practically complete. 



The solution is cooled, diluted with water to exactly 200 cc, shaken, 

 and filtered. One hundred cubic centimeters of the filtrate are treated 

 with 10 grams of potassium iodid and 1 gram of potassium hydroxid, 

 and stirred until solution is complete. Fifty cubic centimeters of 96 

 per cent (by volume) alcohol are now added and the mixture allowed to 

 stand until the following day. The precipitated glycogen is then 

 removed by filtration and washed with a solution containing 1 cc of 73 

 per cent potassium hydroxid, 10 grams of potassium iodid, 100 cc of 

 water, and 50 cc of 96 per cent (by volume) alcohol. 



The glycogen is then washed with a mixture of 2 parts 96 per cent 

 alcohol and 7 parts water (containing 7 mg of sodium chlorid per 

 liter), dissolved in water, and the remaining traces of proteids removed 

 by the addition of double iodid of mercury and potassium. 



It is often found that the proteids are so completely removed that 

 no precipitate is formed with the double iodid. In such case filtra- 

 tion is not necessary. 



a Arch. ges. Physiol., 1899, 76, 531-542. 



