PHYSICAL Ai^D LITERARY. 403 



alkali, as ol. tartan^ to the blue tinflure 

 produced by the lalt of Hartfell fpaw, itr. 

 changes to a redifh j and if an acid, as 

 oL vitrioli, is added to the vitrioluni Mar^ 

 tisj {e, g. if to a folucion of two, three^ 

 or four grains of vitriolum Martis in eight 

 ounces of water, be dropt one gutt. of oh 

 'uitnoli)y this, with powder of galls, though 

 indeed it changes but flowly, will give 

 a bluej not a redifh tihflure ; and again, 

 if the acid is weakened, by dropping^ntd 

 this blue tindure oL tartaric the blue will 

 change to a redifli. And this conjeclure 

 ieems to be confirmed by the: following 

 experiment, viz. if vitriol. Mart, be burnt 

 on a hot iron, till it becomes quite dry^ 

 and of a yellowilh brown» and difTolved 

 in water, it gives much the fame redilh 

 purple with galls, as before it was burnt ; 

 if this hurnt/al Martis be powdered, and 

 the dry powder wrapt up in a fingle pa- 

 per, and left in a room without a fire, 

 for three or four weeks, it will become 

 moift, and, when difTolved in water, ftrikes 

 with galls no more the former colour, but 

 «blue; which, I prefume, is owing to 



the 



