196 QUANTITATIVE ANALYSIS. 



and which is not too small, bring the albumin complete^ on 

 the filter with the aid of a glass rod, wash with hot water 

 until a portion of the wash-water no longer gives the reaction 

 for chlorides, pour the filter full of absolute alcohol twice, 

 then twice full of ether, dry at 110-115 to constant weight, 

 and weigh. If the quantity of the albumin is considerable, it is 

 necessary to incinerate the filter and albumin and to deduct 

 the weight of the ash found from the weight of the albumin. 

 In this case, of course, an ash-free filter must be used. 



X. DETERMINATION OF GLUCOSE. 



Two principal methods are in use, the determination 

 by means of the optical rotation and the reduction of cupric 

 oxide to cuprous oxide in alkaline solution. For practice 

 in the determination of glucose, first use a 3 to 4 per cent, 

 solution of glucose and then a diabetic urine or a 3 to 4 

 per cent, solution of glucose in urine. 



(a) Determination by Means of Polarized Light. 



Before using the polarization apparatus the correct posi- 

 tion of the zero-point must be determined. All readings 

 must be noted in figuring the mean. The filling of the 

 tube is done as follows : First wash it out with distilled water, 

 then two or three times with the solution to be analyzed. 

 This precaution is absolutely essential. If it is omitted, 

 streaks are formed in the fluid owing to the gradual mixing 

 of the sugar solution with the water adhering to the walls 

 of the tube. These interfere with the observation in exactly 

 the same way as they would if in the glass cover-plate, or 

 lens. After thorough rinsing, place the tube on the table, 

 pour it full of sugar solution or urine, so that the fluid forms 

 a rounded top, and slide on, from the side, the well-cleaned 

 cover-plate, so that all air-bubbles are excluded. Then screw 

 on the brass cap moderately tight. The cover must not 



