86 



MILK AND DAIRY PRODUCTS PART 



saturated solution of sodium fluoride, should also be adopted, 

 for it removes the dissolved lime salts, which otherwise would 

 affect the result of the analysis, from the solution. After the 

 precipitate has been allowed to settle for about half an hour, 

 the flask is filled to the mark and the clear solution filtered 

 through a dry folded filter. Fifty c.c. of Fehling's solution 



(25 c.c. of copper solution and 25 c.c. of 

 sodium potassium tartrate solution) 

 are heated in a deep porcelain basin, 

 and, when boiling, 100 c.c. of the 

 filtrate previously obtained are added. 

 After the mixture has again been 

 brought to boiling point it is boiled 

 for exactly six minutes, and then 

 filtered at once through an Allihn 

 asbestos filter, which has been pre- 

 viously washed and dried, either in 

 a current of dry air or over the 

 flame, and weighed. The asbestos 

 filter is fitted into a filter flask, which 

 is in communication with a pump 

 (see Fig. 47). 



By means of a cork a small glass 

 funnel is fitted on to the mouth of 

 the filter, and during filtration a 

 slight vacuum is maintained. The 

 filter and its contents are washed, 

 first with boiling water, then with 

 alcohol (twice), and with ether 

 (twice). 



After the asbestos filter has been dried, it is connected 

 with a hydrogen apparatus, and when the air has been displaced 

 the tube is heated by means of a small flame placed some 

 5 cm. below it. At the end of a few minutes the reduction 

 is complete, and the asbestos filter tube along with the metallic 

 copper is weighed after it has cooled and a current of air has 

 been drawn through. One mg. copper is almost exactly 

 equivalent to 0*73 mg. milk sugar. The table in the Appendix 

 shows the weight of milk sugar equivalent to the weight of 

 reduced copper which has been found. 



FIG. 47. Filtration through 

 the Asbestos Filter in the 

 Allihn -Soxhlet Method. 



