R DAIRY PRODUCTS. 113 



iit they can be filtered and polarized within a few minutes of the time 

 the introduction of the reagents, the suggestion is seen to be of no 

 force. 



For example, in the acid mercuric nitrate it was found that the per- 

 centage of sugar was the same whether one, five, or ten cubic centime- 

 ters of the reagent were employed, and whether it was polarized imme- 

 diately or after heating and cooling. It is evident that Ice. of the re- 

 agent, containing less than a half cubic centimeter of nitric acid and 

 diluted in lOOcc. of liquid, could not exert any notable effect on the 

 rotatory power of the solution. 



In the mercuric iodide solution 20cc. of acetic acid are used for every 

 GGOcc. of the reagent. 



Thirty cubic centimeters of this reagent contain, therefore, about Ice. 

 of acid. This in lOOcc. of liquid, immediately filtered and polarized, 

 could not affect in any marked degree the rotatory power. 



Since combustion with soda-lime shows that the filtrate from the mer- 

 curic iodide sample is practically free from albumen, it is evident that 

 the numbers obtained in this way must be a near approximation to the 

 truth. 



THE PROCESS OF ANALYSIS. 



The reagents, apparatus, and manipulation necessary to give the most 

 reliable results in milk sugar estimation are as follows: 



Reagents. (1) Basic plumbic acetate , specific gravity 1.97. Boil a sat- 

 urated solution of sugar of lead with an excess of litharge, and make it 

 of the strength indicated above. One cubic centimeter of this will pre 

 cipitate the albumens in 50ec. to GOcc. of milk. 



(2) Acid mercuric nitrate, dissolve mercury in double its weight of 

 nitric acid, specific gravity 1.42. Add to the solution an equal volume 

 of water. One cubic centimeter of this reagent is sufficient for the 

 quantity of milk mentioned above. Larger quantities can be used 

 without affecting the results of polarization. 



(3) Mercuric iodide with acetic acid (composition already given). 

 Apparatus. (1) Pipettes marked at 59.5ec., GOcc., and 60.5cc. (2) 



Sugar llasks marked at 102. Ice. (3) Filters, observation tubes, and 

 polariscope. (4) Specific gravity spindle and cylinder. (5) Thermom- 

 eters. 



MANIPULATION. 



(1) The room and milk should be kept at a constant temperature. 

 It is not important that the temperature should be any given degree. 

 The work can be carried on equally well at 15 0., 20 0., or 25 C. The 

 slight variations in rotatory power within the above limits will not affect 

 the result for analytical purposes. The temperature selected should be 

 the one which is most easily kept constant. 



(2) The specific gravity of milk is determined. For general work 

 this is done by a delicate specific gravity spindle. Where greater ac- 

 curacy is required use specific gravity flask. 



19330 No. 13 3 



