OFFICIAL METHODS OF BELGIUM AND HOLLAND 309 



described. The residues are washed 2 or 3 times by decantation with 

 boiling water, finally collected on a weighed filter, washed with hot 

 alcohol and with ether, dried at 100° C, and weighed. The ash is 

 determined in the residue thus obtained and its weight deducted in 

 calculating the cellulose. 



Cellulose is also determined by means of the Hold efleiss method. In 

 this case 3 gm. of the material and 200 cc. of 1.25 per cent sulphuric 

 acid are placed in a Holdefleiss flask and the solution kept at the boil- 

 ing point for h hour by the injection of steam. The material is col- 

 lected on an asbestus filter and washed with hot water until the filtrate 

 is no longer acid. The residue is treated in the same manner with 200 

 cc. of potassium hydrate, the washing being continued in this case 

 until the alkaline reaction disappears. The residue is then washed 

 with alcohol and ether, dried, and weighed. It is then incinerated and 

 weighed again. The difference between the two weights gives the 

 crude cellulose. 



PREPARATION OF SPECIAL REAGENTS. 



Ammonium nitromolybdate. — Dissolve 150 gin. of ammonium molyb- 

 date in 1 liter of distilled water, pouring the solution into 1 liter of 

 nitric acid of 1.2 sp. gr. 



Magnesia mixture. — Dissolve 100 gm. of crystallized magnesium 

 chlorid, 200 gm. of crystallized ammonium chlorid, and 400 gm. of 

 ammonia of 0.96 sp. gr. in water, making the volume up to 1,250 cc, 

 and filter after standing IS hours. 



Alkaline ammonium citrate. — Dissolve 500 gm. of citric acid in just 

 enough ammonia of 0.02 sp. gr. to give a neutral reaction (about 700 

 cc). On cooling add water until the specific gravity is 1.09 at 15° C. 

 Add 50 cc. of ammonia of 0.92 sp. gr. to each liter of this solution, stir, 

 let stand for 48 hours, and filter. The specific gravity of the solution 

 thus obtained is from 1.082 to 1.083. 



Stutzers reagent. — Dissolve 100 gm. of crystallized copper sulphate 

 in 5 liters of water, add about 2 gm. of glycerin, and precipitate the 

 cuprous hydi'ate by adding dilute soda solution until the reaction is 

 faintly alkaline, filter, and diffuse the precipitate in water containing 5 

 gm. of glycerin per liter. Wash by decantation until the precipitate 

 is free from excess of alkali. The precipitate is finally diffused in water 

 containing glycerin and kept in a dark place in a closely stoppered 

 flask. The amount of copper oxid in the reagent is determined by the 

 evaporation and ignition of 10 cc. of it. 

 8192— jSo. 4 2 



