108 78. BASES AND ACIDS WITH REAGENTS. 



column headed specific gravity at 15° C, in Table lY, 

 and against that will be found the per cent of tannic acid 

 in the solution examined. A simple calculation will then 

 give the per cent of the acid in the bark. 



To prepare the powder of skin required in this analy- 

 sis, wash a piece of skin, that has been prepared for 

 tanning by treatment with lime and other agents, with 

 water, stretch it on a board, dry it with the aid of a gentle 

 heat, and rasp it with a coarse file. Keep the powder in 

 a well stoppered bottle. 



CELLULOSE. C12H20O10. 324. 



78. Cellulose is insoluble in water, dilute acids or al- 

 kalies, alcohol, ether, or oils. It is soluble in an ammonic 

 solution of cupric oxide, and is precipitated from this so- 

 lution in the form of colorless flakes. 



Strong sulphuric acid, composed of four parts of acid and 

 one of water, disintegrates it at ordinary temperatures 

 without coloring it, and, after a time, changes it into 

 dextrine. With iodine solution this disintegrated cellulose, 

 before its passage into dextrine, gives a violet-blue color. 



Quantitative estimation. — Cellulose is estimated quan- 

 titatively by freeing it as completely as possible from all 

 other substances, and weighing the residue as pure cellu- 

 lose ; the best method yields results, however, that are 

 about l**|o too high. 



A quantity of 3 to 4 grms. of the substance is exhaust- 

 ed with water, alcohol, and ether, successively, as long as 

 each of these solvents takes anything into solution, and 

 is then macerated 10 or 12 days in a glass-stoppered bot- 

 tle, at a temperature not above 15° C, Avith 12 grms, of 

 nitric acid (Sp. Gr. = 1.1), and 0.8 grm. of potassic chlo- 

 rate ; water is then added, the mixture is filtered, and 

 the filter is well washed, first with cold and afterwards 

 with hot water : the contents of the filter are then rinsed 



