CH. XIV] CELLULOSE. 293 



represents the glucose produced from the starch in the 

 original material. 



In the few cases in which it is necessary to estimate 

 cellulose the residue from starch estimation can be used. 

 The residue is shaken with ammonia, washed and then 

 treated with dilute bromine water as long as the latter is 

 decolorised, if much bromine is required it is better to 

 treat again with ammonia and repeat the oxidation with 

 bromine, the residue is then washed with ammonia and 

 finally with water, dried at 100° and weighed as cellulose. 



The 7'ationale of the process is that substances other 

 than cellulose are oxidised by the bromine water to pro- 

 ducts soluble in alkali, but the cellulose is not altered. 



Experiments on Starch. 



Quantitative. 



I. Estimate the amount of starch in the potato by 

 the processes given on p. 292. 

 Dry at 100° C. and :— 



(a) Extract (1) with alcohol, (2) with cold water, 

 (3) with 1 p.c. sulphuric acid at 100° C. 



(b) Extract (1) with alcohol, (2) with cold water, 

 (3) with malt extract (diastase) at 50 — od"" C. 



(c) Also estimate the starch in another portion of 

 the same by specific gravity and tables. 



This can be conveniently performed by floating the 

 potatoes in a saturated salt solution and adding water till 

 they just sink ; the specific gravity of the fluid, taken with 

 an accurate hydrometer, then equals the sp. gr. of the 

 potatoes. 



