SUGAR 111 



graduations at the 12.5 c.c. and 25 c.c. mark, and 1 c.c. of 20 per 

 cent (anhydrous) sodium carbonate solution is added. The tube 

 is plugged with cotton and immersed in boiling water for ten 

 minutes. (Longer heating up to half an hour makes no change 

 in the color.) It is then removed, and the contents are cooled 

 under running water and diluted to 12.5 c.c. or to 25 c.c. depend- 

 ing on the depth of color. (Occasionally the final filtrates in this 

 or other picric acid methods develop a little turbidity during 

 heating. Unless such turbidity is fairly marked it is of no account. 

 When desired, the final colored solution may be filtered through a 

 small folded filter into the colorimeter cup.) At any time within 

 a half an hour the colored solution is compared in a colorimeter 

 with a suitable standard solution, the standard being set at a 

 height of 15 mm. 



The standard solution may be simultaneously prepared from 

 pure glucose by treating 0.64 mg. of glucose in 4 c.c. of water with 

 4 c.c. of the picrate-picric acid solution and 1 c.c. of the carbonate, 

 and heating for ten minutes in boiling water and then diluting to 

 12.5 c.c. A permanent standard solution may be prepared from 

 picramic acid or from potassium dichromate as mentioned below. 

 The potassium dichromate standard does not match the unknown 

 with absolute exactness, but can be employed with satisfactory 

 results when pure picramic acid is not obtainable. 



Calculation. If directions are followed exactly the calculation 

 is as follows: 



Reading of standard , . , , 



=-10 = per cent of sugar in the original blood. 

 Heading oi unknown 



Where the final dilution of the unknown is made to 25 c.c. instead 

 of 12.5 c.c. the final figure is, of course, multiplied by two. 



Preparation of Solutions. Picrate-picric Acid Solution. To 

 prepare the picrate-picric acid solution, place 36 gms. of dry 

 powdered picric acid in a liter flask or stoppered cylinder, add 

 500 c.c. of 1 per cent sodium hydroxide solution, and 400 c.c. 

 of hot water. Shake occasionally until dissolved. Cool and dilute 

 to 1 liter. 



Permanent Standard. The picramic acid standard is best 

 prepared from a stock solution containing 100 mg. cf picramic 

 acid and 200 mg. of sodium carbonate per liter. One hundred 



