291 



times used also for removing colouring matters, by assimilating 

 those and rendering them insoluble. It serves also for separating 

 fluid from solid fat-acids (see Part II., Div. III., A, a.) 



White of lead may be used instead of oxyd of lead, and acts even 

 m^ore decidedly in many cases. 



Acetate of magnesia (1 part in 9 parts water) serves sometimes 

 for the fractional precipitation of solutions of soaps containing 

 different fat-acids, in order to facilitate their separation. 



Chloride of lime is used in its clear aqueous solution for bleach- 

 ing the vegetable fibre (see Fibre, p. 82). 



Li7ne, slaked with water as to form the finely pulverulent 

 hydrate, serves only for displacing volatile alkaloids (see Div. III., 

 X.). 



PJwsplioric acid is employed for dissolving protein substances 

 {see Div. III., IV.) ; also for displacing volatile organic acids {Ibid, 

 IX.). 



Sulplmte of soda, Glauber's salt (1 part in 9 parts water), is em- 

 ployed for removing lead from liquids, when carbonates of alkalies 

 have to be avoided; yet, as it does not precipitate the lead com- 

 pletely it is necessary, after filtering, to remove the rest of the 

 lead by means of sulphuret of hydrogen. 



Sulphate of silver (1 part in 200 parts watei-) is employed, before 

 ■distilling the volatile organic acids, to remove hydrochloric acid. 



Sulphuret of hydrogen serves not so much for freeing the bases 

 from any excess of lead-salts (for which purpose the carbonates or 

 sulphates of alkalies are preferable) as for decomposing newly 

 precipitated atid edulcorated lead-precipitates with the view of 

 isolating the acid combined with the lead. The gas obtained from 

 sulphide of iron by means of diluted sulphuric acid has to pass 

 through water in order to get rid of particles carried over 

 mechanically, before it comes in contact with the lead-precipitate. 



Animal charcoal, as finely ground bone-black purified by hydro- 

 chloric acid and heated afterwards to a red heat, is an important 

 means for absorbing pigments, odours and bitter substances, and is 

 even used for isolating the latter pure, by submitting the coal 

 laden with them and after washing with water, to digestion with 

 strong alcohol, which then withdraws the bitter substance or sub- 

 stances. 



Alumina, in its newly precipitated hydrated state, may often be 

 employed with advantage as separating agent, as it precipitates 

 pigments and many other either little coloured or colourless bodies 

 from their solutions and leaves others dissolved. 



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