STUDIES ON FERMENTATION. 3-j5 



wliich I'enclerecl tlie method at the same time surer and more 

 expeditious. 



The principal feature in M. Schiitzenberger's process consists 

 in the employment of a salt, the properties of which that 

 chemist was the first to recognize ; he has named ii hydrosulphite 

 of soda, and it is obtained by the action of zinc filings on a 

 solution of bisulphite of soda, out of contact with air. 



Hydrosulphite of soda S-0~,NaO,HO, which is isomeric with 

 hyposulphite of soda, only differs from the bisulphite by two 

 equivalents of oxygen.* When brought into contact with free 

 oxygen, it absorbs that gas instantaneously and becomes con- 

 verted into bisulphite ; similarl}^ when mixed with water, it 

 immediately absorbs the oxygen held in solution. Again there 

 are colouring matters, such as M. Coupler's soluble aniline blue, 

 that are instantaneousl}^ decolourized by hydrosulphite of soda, 

 whilst they resist the action of the bisulphite. If, taking care to 

 avoid the access of air, we add hydrosulphite of soda to a certain 

 volume of water — a litre, for example — that has been deprived of 

 air and faintly coloured with Coupler's blue, we shall see that 

 a few drops will be sufiicient to effect the decoloration. If, on 

 the contrary, the water is aerated, the decoloration will not be 

 effected before a sufiicient quantity of the hydrosulphite has 



* [As some confusion, has existed in tlie nomenclature of these salts, it 

 may be as well to offer some explanation. 



The salt here used for absorbing oxygen was discovered by Schiitzen- 

 berger, and named by him hydrosulphite of soda. It no longer now goes 

 by that name, being called hyposulphite of soda, NaHSOj. 



The salts formerly known as hyposulphites are now called thiosulphates, 

 as Na^SoOg. 



Thus to put them together we have : — ■ 



Hyposulphite (Hydrosulphite) . . . . NaHS02 



Bisulphite NaHSOs 



Thiosulphate (Hyposulphite) . . . . NasSoOa 



The thiosulphates were formerly regarded as containing the elements of 

 water in their composition, thus : — Na2HoS204, which being halved would 

 give NaHSOo, isomeric with hyposulphite, as Pasteur says. It is 

 further to be observed that Pasteur uses the old notation, in which 

 the number of atoms of sulphur and oxygen are the double of what 

 they are in the new. — D. C. E.] 



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