320 



■witli an excess of burnt magnesia (or finely pulverised oxyd of lead 

 or white of lead), dry in a gentle heat, pulverise, treat with cold 

 water (in order to remove alkali-salts, chloride of magnesium, iodide 

 of potassium, &c.), boil with alcohol of 90°/^, evaporate the alcoho- 

 lic liquid and submit to examination what has remained. 



(d) The remaining liquid may probably contain traces of dyeing 

 matters, of gum and of resin, the further examination of which is 

 perfectly valueless and involves only loss of time. 



YII. — Treatment with Diluted Potash-ley. 



Bring the substance remaining after the treatment with hydro- 

 chloric acid, and while still in a moist state, back into the beaker, 

 add water enough to make the whole up to 500 grams, dissolve 

 in the mixture 10 grams hydrate of potash (or of soda), digest 

 for two days in a temperature of 50° to 60°, let cool, filter and 

 wash the residue thoroughly. 



Dry 5 grams of the residue at 110°, weigh, calculate the 

 weight of the whole residue conceived dry, and subtract this 

 weight from the one obtained under VI., the rest representing the 

 weight of the matters dissolved by the ley. 



Should the mass prove too thick for filtering, it must be diluted 

 previously, and is, if necessary, clarified by subsiding. 



(«) The alkaline liquid is generally more or less brown, some- 

 times black-brown. By over-saturating with hydrochloric acid, a 

 brown, flocky precipitate is invariably obtained, which contains 

 so-called humic acids, but which may also contain protein-sub- 

 stances. The two substances are only incompletely separable by 

 liquor of ammonia, the humic acids being more soluble in it than 

 the protein-substances. For the quantitative estimation of the 

 two bodies it is suflicient to collect the precipitate produced by 

 hydrochloric acid, to wash, to drj at 120°, and to determine the 

 amount of nitrogen by heating with soda-lime. By multiplying 

 with 6i^ the weight of the nitrogen obtained, the quantity of the 

 protein-s\ibstances is determined, and by subtracting the latter 

 weight from that of the precipitate, the weight of the humic acids 

 is obtained. 



(b) The liquid obtained by filtering in a, contains small 

 quantities of humic acids as well as of protein-substances, the 

 closer investigation of which is impracticable. 



(c) The residue left after the treatment with potash-ley, and the 

 dry weight of whicli has been calculated, is generally accounted 

 for as vegetable fibre or cellulose, though this name is not correct, 

 as this fibre contains not only colouring matters but also mineral 

 compounds. Regarding the complete removal of the first and the 

 estimation of the latter impurities, see under Fibre, p. 82. 



