72 LABORATORY MANUAL OF MICROBIOLOGY 



The solution is cooled, neutralized with sodium hydroxide solu- 

 tion, and made up to 500 cubic centimeters. The solution is 

 filtered and reducing sugar (glucose) determined in an aliquot 

 portion. A blank determination of 20 cubic centimeters malt 

 extract boiled with acid as before outHned is subtracted. The 

 amount of glucose calculated is multiplied by 0.9 to give the 

 weight of starch. 



5. Reducing Sugars. — Reducing sugars may be determined con- 

 veniently by the Bertrand or the modified Shaffer and Hart- 

 mann^ method or by any other convenient method. 

 Micro Method. — Prepare the following reagents: 

 (a) Combined micro reagent: 



Grams per Liter 



CuSOrSHzO 5.0 



Tartaric acid 7.5 



NazCOa (anhydrous) 40 . 



KI 10.0 



KIO3 0.7 



Potassium oxalate 18.4 



The sodium carbonate is dissolved in about 400 cubic centi- 

 meters of warm water, and into this, with stirring, is poured the 

 copper sulphate and tartaric acid dissolved in about 150 cubic 

 centimeters of water. The iodate, iodide, and oxalate are 

 dissolved in about 250 cubic centimeters of water, rinsed into 

 the alkaline copper solution, cooled and diluted to a liter. It is 

 usually more convenient to make up a larger quantity based on 

 the same proportion of reagents. 



(5) lA^ H2SO4 — 27 cubic centimeters of concentrated H2SO4 

 are poured into a quantity of water and diluted to a liter. The 

 resulting solution is approximately normal but can be readily 

 adjusted by titration. 



(c) O.IA^ thiosulphate — 25 grams of pure sodium thiosulphate 

 and 1 gram of NaOH are dissolved in water and diluted to a liter. 

 This should give a solution a trifle stronger than O.liV. It can 

 be readily standardized with a solution of O.IA^ K2Cr207. 

 To prepare this solution pure K2Cr207 is dried at 110°C., and 

 4.9033 grams are dissolved in water and diluted to 1 liter. 

 Twenty-five cubic centimeters of the standard dichromate are 



1 Stiles, H. R., W. H. Peterson, and E. B. Fred, /. Bad., 12: 427-439, 

 1926. 



