304 Oft StfLPHUROUS ACtO. 



Reddened again Erp.1. The acids above mentioned, added by little aixt 



acids. 6 0t ^ M^tle to tne blue liquor, restored its former red colour im- 

 mediately ; the acetic acid excepted, the iction of -which 

 was slower by a few minutes, and it required to be added 

 in a pretty considerable quantity. 



Exp. 3. Sirup of violets diluted with a similar quantity 

 of water, and coloured red by oxalic, citric, tartarous, and 

 acetous acids, had its blue colour equally restored by 

 adding a few drops of liquid sulphurous acidr but on the 

 subsequent addition of these acids they exhibited some 

 peculiar properties, which I shall proceed to mention. 



Oxalic acid. 1. The oxalic acid in a small dose produces at first no 



change. It must be added in considerable quantity, to 

 make the liquor assume a violet hue; and several hours 

 elapse, before it resumes its red colour. 



Tartarons, 2. The tartarous, citric, and acetic acids, mixed in any 



citric, and ace- . . , , . . .. , . , 



t0USi proportion with the blue liquor, cannot again make it reef, 



even though it remain exposed to the air for twelve hours. 



The sulphurous 3. In these three experiments the blue colour continues 



acid continues to decrease : which indicates, that the sulphurous acid still 



to diminish the r 



colour. enjoys its property of destroying colours, notwithstanding 



the excess of the other acids. All these experiments were 

 •made in glass vessels open to the air : but it was necessary 

 to ascertain, whether this agent had any inlluencc on the 

 colour of the different mixtures ; for which purpose I re- 

 peated the same experiments in bottles closely stopped., and 

 operating as quickly as possible. 



Experiments made in stopped Bottles. 

 Exclusion of air Exp. 4. Into nine Hint glass bottles with stopples I put 



didnotprev.nt . f . ^ t diluted with water as above, and reddened 



the action of the ^ ' 



sulphurous acid, by the same acids, and ticketed them. Into each phial I 



dropped liquid sulphurous acid, till the blue Colour was re- 

 stored, taking care to shake the mixture well after each drop, 

 and observe the change irulucedjiin its colour. This Ijdid with 

 all the nine phials in succession ; and, stopping them as. I 

 did it, I left them at rest for six hours. In this space of 

 time I observed the blue had lost a H-ttlte of its intensity, 

 without being affected with any tinge of red. 



but modified Erp, b. I had next to examine, whether the acids em- 



the subsequent ■* ' 



ployed 



