6ULPHUKOUS ACID AND SULPHITES EN' DEFECATIOX. 305 



carbonic acid, to remove the lime which remains and which was not 

 thrown down by the first treatment with carbonic acid nor by the 

 boiliug. It is then boiled, passed through bag filters, after having 

 stood in the subsiding tanks fi^r the subsidence of the carbonate of 

 lime, and is ready for concentration. In expert hands, the process 

 is most highly commended. Details may be found in " Sugar Growing 

 and Eetining." 



SULPHUROUS ACED AND SULPHITES IN DEFECATION. 



The employment of this re-agent in the defecation of saccharine 

 juices was suggested by Proust, in 1810, and has been very general, 

 and the results attending its use seem to justify it. This gas is the 

 product of burning sulphur, and is readily made available by burning 

 sulphur in such a way that the products of the combustion may be 

 drawn from the furnace and brought in contact directly with the juice, 

 or with water, in both of which the gas is very soluble. 



The bleaching properties of sulphurous acid are well known ; and it 

 is, owing to its tendency to unite with oxygen to form sulphuric acid, 

 one of the most powerful deoxidizing or reducing agents. It is also, 

 by some, regarded as an antiseptic (preservative), and as a disinfec- 

 tant ; but whatever action it may have in this way is probably due 

 to its removal of the oxygen of the air, and the destruction of the pro- 

 ducts of decomposition by its reducing power. 



It will readily dissolve in water, one volume of water at 27° C. 

 (81° F.) dissolving about 30 volumes of the gas, or at 21° (70° F.) 

 38 volumes, and at 16° C. (61° F.) 45 volumes; so that it may, by 

 being dissolved in water, be easily prepared and kept for use, the only 

 precaution necessary being to keep it in closely corked bottles, or 

 casks, so as to exclude the air, the oxygen of which will unite with it, 

 and, in time, convert it entirely into sulphuric acid, a substance which 

 exercises the most injurious action upon sugar by converting it into 

 glucose. 



Sulphurous acid may be readily prepared by the reduction of sul- 

 phuric acid (oil of vitriol) by means of charcoal, according to the 

 following re-action : 



Sulphuric acid + Charcoal = Water -^ Carbonic acid -i- Sulphurous acid- 

 2(H2S04) -^ C =2H20+ CO2 + 2SO2 



Or, by weight, as foUows ; 



Sulphuric acid -fCharcoal = Water + Carbonic acid + Sulpharons acid. 

 196 parts —12 parts =36 parts + 44 parts + 128 parts. 



20 



