[ 338 ] . 



deteded by a vlfible blue tinge appearing on tlie 

 addition of a few drops of volatile akali, yet this is* 

 by no means the cafe in turbid high-coloured 

 liquors, which intercept the rays of light, and often 

 occafion a confiderable deception in the appearances. 

 Hence the nccefTity of diluting fuch liquors in va- 

 rying the experiments. In no inflance did the blue 

 tinge appear with the alcalies, even after the wine 

 was dilutedj and yet its ablcnce does not prove the 

 liquor to be abfoiutely/rftf from an impregnation 

 of copper. For I afterwards found that it required 

 from three to five drops of a folution of vitriol cf 

 copper to give a vifible blue tinge to a glafs of the 

 ^liqudi*. The akali^s gave agreenilh tinge to the 

 wine} and copper, in form of vcrdegris, afTumes 

 indifferently a green or blue colour, according to 

 circumftances. 



If the mark on pollfhed iron was darker than 

 that which is produced by vitriol of copper, it was 

 evidently owing to a fmall portion of the iron dif- 

 folved at the fame time, and which always imparts 

 a hlackijh tinge to polifhed metals. 



If the liquor was free from any metallick impreg- 



^nationj why did it yield ^ precipitation? — a 'y^rzV- 



gatcd Jih}2i'—'2L broum Jediment? And why did it 



afford 



