THE ANALYSIS OF MILK 



33 



from the sides of the beaker by rubbing with a police- 

 man, and transferred to the tube ; the precipitate in 

 the tube is well washed with hot water, and finally 

 with alcohol, and dried. The narrow end of the tube is 



FIG. 22. Washing Precipitate. 



connected with an apparatus from which hydrogen can 

 be evolved, and after the stream has passed for a few 

 minutes the part of the tube containing the precipitate 

 is gently heated by a small flame, till the cuprous oxide 

 is reduced to copper; the hydrogen is passed till the 

 tube is cool, and it is then disconnected and weighed ; 

 the increase in weight gives the quantity of copper, 



c 



