288 



METHODS OF ANALYSIS 



[Chap. 



ALBUMIN. 



6 Method I. — Tentative. 



Exactly neutralize the filtrate, obtained in 4, with sodium hydroxid solution, 

 add 0.3 cc. of 10% acetic acid and heat on a steam bath until the albumin is com- 

 pletely precipitated. Collect the precipitate on a filter, wash with cold water and 

 determine the nitrogen as directed under I, 18, 21 or 23, multiply by 6.38 and cal- 

 culate the percentage of albumin. 



7 Method II. — Tentative. 



To the filtrate obtained from the casein determination, 5, add 0.3 cc. of 10% acetic 

 acid, boil until the albumin is completely precipitated and proceed as directed in 6. 



LACTOSE. 

 Optical Method. — Tentative. 



8 REAGENTS. 



(a) Acid mercuric nitrate solution. — Dissolve mercury in double its weight of 

 nitric acid (sp. gr. 1.42) and dilute with an equal volmne of water. 



(b) Mercuric iodid solution. — Dissolve 33.2 grams of potassium iodid and 13.5 

 grams of mercuric chlorid in 20 cc. of glacial acetic acid and 640 cc. of water. 



9 DETERMINATION. 



Determine the specific gravity of the milk by means of a delicate hydrometer 

 or, if preferred, a pycnometer. The quantity of sample to be taken for the deter- 

 mination varies with the specific gravity and is to be measured at the same tempera- 

 ture at which the specific gravity is taken. The volume to be measured will be 

 found in 10 which is based upon twice the normal weight of lactose (32.9 grams per 

 100 metric cc.) for the Ventzke sugar scale. 



Place the quantity of milk indicated in 10 in a flask graduated at 102.6 cc. Add 

 1 cc. of the acid mercuric nitrate solution or 30 cc. of the mercuric iodid solution 

 (an excess of these reagents does no harm), fill to the mark, shake, filter through a 

 dry filter and polarize. It is not necessary to heat before polarizing. If a 200 mm. 

 tube is used, divide the polariscope reading by 2 (or, if a 400 mm. tube is used, by 4) 

 to obtain the per cent of lactose in the sample. 



10 



Table 19. 



Volumes of milk corresponding to a lactose double normal weight^ 



