SULPHITATION 295 



Baryta. — Although essentially similar to lime in action, baryta preci- 

 pitates sulphates and some other bodies not thrown out by lime, and for 

 this reason its use has been advised. Questions of cost, however, render 

 its use in the quantities required impossible. In white sugar manufacture 

 baryta is, however, sometimes used on s\Tups where the bulk}' precipitate 

 formed is believed to carr}' down iron as ferric hydrate. 



Ferrocyanide. — Iron present as a ferrous salt may be quantitatively 

 precipitated by potassium ferrocyanide and removed b\' filtration. If 

 allowed to remain suspended, the white compound formed is oxidized to 

 Prussian blue. This reaction is employed on s\Tups in white sugar manu- 

 facture, the salt being used in quantities of about i oz. per ton of syrup, which 

 is enough to precipitate the very small quantities of iron present. 



Potash Removal. — The removal of potash from juices has been attempted 

 in man\- ways. In chronological order the proposals are : — Kessler, French 

 patent 58613, 1862 ; Marix, French patent 82562, 1868 ; Tamin, patent 

 315 1 of 1873 ; Hlavati, 15274 of 1903, precipitation as fluosilicates ; Duncan 

 and Newlands, 2090 of 1871, precipitation as tartrate ; Duncan, 1989 of 

 1874, precipitation as a potash alum ; Gill and Gill, 3333 of 1874, precipi- 

 tation as oxalate ; Gans, 8232 of 1907, substitution of potash by lime 

 obtained by filtering through an artificial zeolite, with subsequent recovery 

 of the potash by washing. Of these proposals the recovery as an alum was 

 successfully worked for a number of }'ears in a London refiner}'. 



Electrical Processes. — Though the passage of a current does afford a 

 coagulation of the colloids, the same effect can be obtained in a better and 

 cheaper way by the action of heat and lime. Various proposals and processes 

 depend for their effect, not on the passage of the current, but on the solution 

 of the heavy metal forming an electrode. Other proposals of this nature 

 have all the appearance of being frauds, and the secrecy attached to them 

 does not invite confidence. 



Heavy Metals. — Nearly cdl the heavy metals form bulky precipitates with 

 cane juices. This is especially the case with basic lead salts, the use of which 

 and their subsequent removal as phosphates formed the subject of a patent 

 issued to Gwynne and Young (7231, 1836). Later Scoffern's proposal 

 (patent 11991, 1847) to use lead and eliminate it as sulphite enjoyed a brief 

 period of notoriety. It was used in a London refinery under the supervision 

 of Daniell, and also in Spain and the West Indies. Authority finally inter- 

 vened to stop its use. The use of tin salts was patented by Nash (366 of 

 1852), and of zinc by Terry and Parker (6442, 1833). 



The Use of Vegetable Carbons. — About 1910 certain preparations consisting 

 essentially of finely divided carbon appeared on the market, the object of 

 their production being the decolorization of sugar materials. Great mystery, 

 extravagant claims, and exorbitant prices were attached to these prepara- 

 tions, which, however, may become of great value to the industry. 



A certain amount of research work has been done on these materials, and 

 an abstract of the present state of knowledge is appended : 



Preparation. — A charcoal prepared by carbonizing wood at a low tempera- 

 ture will be found to have little if any adsorptive properties. It may, how- 



