114 FOODS AND FOOD ADULTERANTS. 



(3) If the specific gravity be 1.026 or ueaiiy so, measure out 60.5cc. into 

 the sugar flask. Add Ice. of mercuric nitrate solution or 30cc. mercuric 

 iodide solution and fill to 102.4cc. mark. The precipitated albumen occu- 

 pies a volume of about 2.4cc. Hence the milk solution is really lOOcc. 

 If the specific gravity is 1.030 use 60cc. of milk. If specific gravity is 

 1.034 use 59.5cc. of milk. 



(4) Fill up to mark in Iu2.4cc. flask, shake well, filter, and polarise. 



NOTES. 



In the above method of analysis the specific rotatory power of milk 

 sugar is taken at 52.5, and the weight of it in lOOcc. solution to read 100 

 degrees in the cane sugar scale at 20.56 grams. This is for instruments 

 requiring 16.19 grams sucrose to produce a rotation of 100 sugar de- 

 grees. It will be easy to calculate the number for milk sugar whatever 

 instrument is employed. 



Since the quality of milk taken is three times 20.56 grains, the polar- 

 iscopic readings divided by 3 give at once the percentage of milk sugar 

 when a 200mm. tube is used. 



If a 400inrn. tube is employed, divide reading by 6; if a 500mm 

 tube is used, divide by 7.5. 



Since it requires but little more time, it is advisable to make the 

 analysis in duplicate, and take four readings for each tube. By follow- 

 ing this method gross errors of observation are detected and avoided. 



By using a flask graduated at 102.4 for 60cc. no correction for volume 

 of precipitated caseiue need be made. In no case is it necessary to 

 heat the sample before polarizing. 



ESTIMATION OF THE ALBUMINOIDS. 



The albuminoids in milk are most easily estimated by combustion 

 with soda-lime or by previous conversion into arnrnoiiic sulphate and 

 subsequent distillation from an alkaline liquid. 



(1) Combustion with soda-lime From 4 to 5 grams of milk measured 

 from a weighing flask are evaporated to dryness in a schalehen either 

 alone or wiih sand, gypsum, pumice-stone or asbestos. When dry the 

 whole is rubbed up in a mortar, transferred to a combustion tube, and 

 burned in the usual way. The nitrogen calculated from the ammonia 

 formed multiplied by 6.25 gives the total albuminoids. 



(2) The estimation of the albuminoids by Kjeldahl's method is so 

 well understood that it will not be necessary to describe it here. 



Following are the results of the analyses of milks made in this labo- 

 ratory. 



In table No. 14 are the results of the daily analyses of milk from 

 the Maythorpe Dairy. 



In table No. 15 are the numbers obtained with milks from various 

 sources. 



In these analyses the fat was estimated by the modified Soxhlet 

 method, the sugar by the optical method, and the albuminoids by com- 

 bustion with soda-lime. 



