SULPHUROUS ACID A>"D SULPHITES EN' DEEEtATIO>r. oCW 



and it is cLiimed that the sulphurous acid reuders certain of these im- 

 purities of the juice insoluble, and thus effects their removal in the set- 

 tling tanks. This is a matter requiring and deserving very careful 

 investigation. 



The general use of sulphurous acid is, however, in the sulphur box, 

 where the freshly expressed juice, on its way to the storage tank and 

 immediately 2:)revious to its defecation with lime, is charged with this 

 gas ; or the juice, after defecation and the separation of scum and sedi- 

 ment, is treated with the sulphurous acid, imtil the juice, which had 

 been rendered slightly alkaline by the lime, is rendered acid again. 



The addition, at this stage, changes the color of the defecated juice, 

 bleaching the color which still remains, and greatly improving the 

 appearance of the juice. Any excess of the acid which may be added 

 is removed readily during the evaporation, since the gas is verv 

 volatile. 



Any small quantity of sulphuric acid which may be present in the 

 sulphurous acid used, will be renderetl harmless by the slight excess of 

 lime present, and will form the insoluble sulphate of lime, wliich may 

 be removed as sediment or skimmings in the process of manufiacture. 

 So far as the results of the author's experiments go, there appears to 

 be no choice in the two methods, above described, of using the sid- 

 phurous acid ; and. indeed, it seems that the advantages claimed for it 

 are greatly over-estimated. It is certain that, by pn>mpt working of 

 the cane, the results, without its use, have proved as satisfactor}- as 

 with it. In case of delay in working up the juice, it would appear that 

 the use of the gas as a temp<5rary antiseptic is beneficial. It is prol>- 

 ably true that, by its oxidation, it forms sulphuric acid, which, with 

 the soluble potash salts present in the juices and retauaed by the svrup, 

 forms the comparatively insoluble sulphate of potash, a salt which has 

 been found not to retard the crystallization of the sugar in the syrup. 



At the large sugar factory at Aba-^l-Wakf, in Egypt, the juice was 

 first treated with sulphurous acid previous to the limiug, and the re- 

 sults showed excellent returns in sugar; but it does not appear that the 

 good results were due any more to the use of sulphurous acid, than to 

 the many improved appliances of this famous mill. It must he 

 remembered, that the bleachiug by sulphurous acid is onlv temporarv, 

 the color being only masked, but not destroyed ; so that the ap- 

 parent action of this re-agent is very deceptive, and not comparable 

 with that of bone-black, wliich completely removes the color fix>m the 

 juice or syrup. 



