298 TITRIMETRIC METHODS 



2. Add about 40 fd. carbonate soln. and the same vol. ferricya- 

 nide soln. 



3. Add water to the calibration mark* and place in boiling water 

 for 5 min. 



4. Transfer to a porcelain titration dish with a pipette and use 

 successive rinsings with water to insure a quantitative transfer.* 



5. Add 50 ixl. 10% sulfuric acid and a little phenanthroline 

 indicator. 



6. Titrate with eerie sulfate to the first permanent grass-green 

 color. 



7. Run control by substituting water for the sugar soln. 1 [xg. 

 glucose requires 2.556 /xl. 0.01 A^ eerie sulfate. 



note: For the deproteinization of blood, Heck et al. pipette sample into 

 calibrated tube having a vol. about ten times that of the sample. The 

 pipette is then rinsed into the tube,* a vol. of 10% copper sulfate 

 (CuSOi.SHaO) equal to that of the sample is added, and while stirring 

 a similar vol. of 10% sodium tungstate in 2% sodium carbonate is added 

 slowly. The soln. is made up to the calibration mark with water,* stirred, 

 centrifuged, and the supernatant is drawn off and used. 



GLYCOGEN 



Heatley ( 1935) described a micro determination of glycogen 

 based on the isolation of glycogen from tissue, acid hydrolysis, and 

 estimation of the reducing sugar formed by the method of Linder- 

 str0m-Lang and Holter (1933a). The procedure of Heatley may be 

 applied to amounts of tissue of the order of 1 mg. The maximum 

 error is less than ±2 fig. glycogen corresponding to ±0.3 jul. 0.05 N 

 thiosulfate. The loss of about 1.5% which occurs during the pre- 

 cipitation of the glycogen is approximately compensated by stand- 

 ardizing the reagents through a control estimation of a glycogen 

 solution of known strength. Subsequently Heatley and Lindahl 

 (1937) extended the method to include the separation of desmo- 

 and lyoglycogen, according to the principles given by Willstatter 

 and Rohdewald (1934), and the measurement of the two forms 

 individually. For a colorimetric method see page 247. 



*It would be well to simplify these steps as indicated on page 165. 



