34* COMBINATION OF MERCURY 



is a mild phagedicnic water, with two grains 

 only of corroiivc mercury to the ounce. The 

 fixed alkali produces no eiVect on it ; but the vo- 

 latile feparates a very fmall portion of a white 

 powder. The pharmacopoeia of Paris and Straf- 

 burg have both this formula of the aqua pha- 

 ged;enica ; but it may be more eilicacioufiy pre- 

 pared, if necefliiry, when it is exactly known 

 \vhut quantity of corrolive mercury can be ei- 

 ther diflolved or precipitated by lime-water. 



For the purpoie of determining whether an 

 Alkali is prefent in any fluid, and of what kind 

 it is, the corroiive mercury may be convenient- 

 ly employed. As foon as a fmall portion of this 

 fait is thrown into it, it is tinged according to 

 the nature of the alkali with a yellow or red co- 

 lour, or is clouded with u white powder; if it 

 contains no alkali, it remains unchanged. 



An infufion of galls mixed in a folution of 

 corrofive fublimate renders it thick and black. 

 The precipitate on being dried ailumes the co- 

 lour of umber. 



$ xiv. IViib Metals, 



MOST metals decompofc corrofive mercury. 

 Stuhl has obfervcd that it deliqucfces, ii' pow- 

 dered tin or iron are fprinkled on it, and that 

 theic metals arc corroded with the muriatic a- 

 cid *. Junker alfo informs us, that if a fojution 



of 



* Spec. Bcch. 1703, 1720. 



