CANE SUGAR. 



FIG. 255. 



thus: A plug of glass wool is placed on the concave bottom of the tube 



and above this a pad of asbestos ; the plug of glass wool should be about f in. 



deep and the asbestos about T ^ ; the best quality of asbestos must be used and 



previous to use it should be digested, first in 

 caustic soda, then in nitric acid, and finally in 

 water. After the Soxhlet tube has been pre- 

 pared, it is fitted into the stopper of the filter 

 flask and filled about three parts full with water; 

 a small funnel is then fitted on to the tube, the 

 stem of which does not quite reach to the level 

 of the water in the tube ; the funnel is then 

 filled with water and the pump started ; as the 

 water passes through the filter, the liquid under- 

 going filtration is poured into the funnel, care 

 being taken to keep the funnel full; when 

 all the copper oxide has been brought into 

 the funnel; the level of liquid is maintained by 



hot water until all the precipitate has passed into the Soxhlet tube and is 



continued until the washing is complete. 



C. A Grooch crucible consists of a tall crucible of conventional pattern, 



the bottom of which is a perforated disc ; it is prepared for use as described 



for the Soxhlet tube, save that the pad of glass wool is unnecessary. 

 The filtration apparatus used in the 



laboratories of the Hawaiian Sugar Planters' 



Association is shewn in Fig. 256 ; the filter 



flask is of the form due to Diamond. The tube 



a communicates with the vacuum pump ; con- 

 nection with the atmosphere may be made by 



the cock on the tube I ; the Gooch crucible c 



is held in the carbon tube d, a tight joint being 



made by a piece of inner tubing of a bicycle 



tyre ; the filtrate may be discharged through 



e. The advantages of this apparatus for all 



vacuum nitrations are obvious. 



The Determination of the Re- 

 duced Copper. A. As Cuprous Oxide. 

 The cuprous oxide after collection by one or 

 other of the above methods is dried to con- 

 stant weight, preferably in a vacuum oven, or else at 105C. The drying is 

 materially accelerated by washing the precipitate first with alcohol and then 

 with ether. 



B. As Cupric Oxide. If the cuprous oxide has been collected on paper 

 the precipitate is, after drying, detached as completely as possible from the 



460 



FIG. 256 



