Observations on the Sulphurous Add. 173 



was prepared bv the decomposilioii of very pure sulpliuric 

 acid upon equaliv .^ri. merci" * ii!. respect to ihc ma- 



nual opera in, 1 i.. ';;\\cd tuai wluch was pointed out by 

 M. B .1. 



Tiv V net syrup was a very fine blue, without mixture. 



First FjTperiment. — Syrup of violets diluted with eight parts 

 of distilled water, and coloured red bv the nitre, muriatic, 

 sulphuric, pliosphoric, or acetic acids, resumes, upon the 

 addition of liquid sulphurous acid, its blue colour, a little 

 less intense, to be sure, than before its change into red ; 

 but without any mixture of this last colour. 



Second Experiment. — The above acids, added gradually 

 to the blue liquor, instantly restore its primitive red colour, 

 the acetic acid excepted, the action of which is some minutes 

 slower, and it must be added in a larger quantity. 



Third Experiment. — Syrup of violets diluted with a simi- 

 lar quantity of water, and coloured red by the oxalic, citric, 

 tartarou?, and acetous acids, also becomes blue upon adding 

 some drops of liquid sulphurous acid ; but these acids pre- 

 sent, in their subsequent employment^ som.e peculiar pro- 

 perties, which I shall detail : 



1st. The oxalic acid, in a small quantity, produces no 

 change at first : we must add a considerable quantity, in 

 order to give the liquor a violet hue, and it is some hours 

 before it resumes its red colour. 



2d. The tartarous, citric, and acetous acids, mixed in any 

 proportion with the blue liquor, cannot make it become red 

 again, even after being 12 hours exposed to the air. 



£fd. In these three experiments the blue colour gradually 

 decreased ; which shows that the sulphurous acid continues 

 to enjoy its property of discharging colours, notwithstanding 

 the superabundance of the other acids. All these trials were 

 made in earthen vessels, and exposed to the air ; but it became 

 necessary to ascertain if this agent had any influence in the 

 colouring of the different mixtures : this is the reason why I 

 repeated the same experiiuents in glass bottles well closed, 

 and operating as hastily as possible. 



Fourth Experiment. — Experiments in close Bottles. I 

 ilistributed in nine glass bottles, furnished with ground stop- 

 pers, 



