32 DAIRY ANALYSIS 



50 c.c. of the filtrate are placed in a beaker, and a 

 mixture of 30 c.c. each of Fehling's copper sulphate and 

 alkaline tartrate solutions (see Appendix) added ; the 

 beaker is heated by a flame of such size that the liquid 



FIG. 21. Polariscope. 



boils in about four minutes, and it is kept boiling for 

 exactly six minutes. A tube of hard glass, about i c.m. 

 in internal diameter and 10 c.m. long, with one end 

 drawn out, and plugged with a fairly tight wad of 

 asbestos, is ignited, cooled, and weighed ; the drawn- 

 out end is inserted in a hole in the cork of a vessel 

 from which the air can be exhausted (e.g. by a filter 

 pump), a small funnel is placed in the wider end, and 

 the liquid carefully poured off from the red precipitate 

 of cuprous oxide ; the precipitate is washed several 

 times by decantation with hot, well-boiled water, and is 

 then washed into the tube, and the last traces removed 



