79. STAKCH. 109 



into a beaker and digested about an hour, at 60° C, with 

 ammoniacal water containing 50 parts of water to one of 

 common ammonia ; the mixture is filtered through a dried 

 and weighed filter, the contents of the filter washed with 

 the same ammoniacal water until the washings are color- 

 less, then with pure water, with alcohol, and finally with 

 ether, dried at 100° C, and weighed. 



This cellulose often contains as much as from 0.5 to 0.7 

 " Iq of albuminoids, and a very small per cent of inorganic 

 matters. 



STARCH. C12H20O10. 324. 



79. Starch, as long as it retains its natural form, is in- 

 soluble in water, alcohol, and ether. In contact with hot 

 water the starch grains swell up, and, if a larger quantity 

 of water is then added, a small portion of the starch re- 

 mains in solution. 



Starch may be converted into a soluble modification by 

 boiling it with water under pressure, by heating it a short 

 time with dilute sulphuric acid, or by the action of dias- 

 tase at ordinary temperatures. 



Dry starch is colored blue or black by a solution of 

 iodine in potassic iodide. The color is destroyed by alco- 

 hol, potassa, or hydrosulphuric acid, or by heat ; if not 

 heated too long, the blue color reappears as the solution 

 cools. 



Quantitative estimation* — Starch is usually determined 

 by conversion into glucose, either by malt or sulphuric 

 acid, and the subsequent determination of the glucose 

 with Fehling's solution. 



1. By malt. — To prepare the extract of malt, crush 6 

 grms. of fresh malt in a mortar, digest with lukewarm 

 water, filter, and wash the filter with water of 60° or 70°, 

 and divide the clear filtrate, after mixing it well with the 

 washings, into two exactly equal parts. Mix a quantity 



