Mcafurement of the Meridian. 2 6$ 



■expect) white precipitates ; tartrite of potafh, a cryftalline 

 irifoluble fait : all properties refembling the hepatifed fo!u~ 

 tion of manganefe. 4. Common iron ruft, purified by boil- 

 ing in diftilled water, was digefted in hepatifed water. In 

 a day or two the hepatic odour is deftroyed, and the liquor 

 has properties fimilar to that which was formed with the 

 iron filings. The fame kind of deliquefcent fait is left by 

 evaporation, (hewing the fame appearances of muriatic acid. 

 However, this liquor refembles the folution of manganefe in 

 precipitating nitrat of filver readily, and of a brown colour 

 (ix. 2.). 5. I treated mercury in the fame way : no gas 

 efcapes in this experiment, as it does with the iron ; a black 

 fubftance is formed ; but the hepatic odour was not deftroyed, 

 though the hepatic gas was kept in contact with the mercury 

 many weeks. After filtrating the liquor, I boiled it to expel 

 the fuperfluous hepatic gas. A fmall portion of the liquor 

 was fuffered to evaporate fponcaneoufly : a cryftalline matter 

 was left behind of an acrid tafte. Another portion was 

 evaporated, with intention to collect more of thofe cryflals ; 

 but, by accident, it was left expofcd to heat too long, by 

 which it became perfectly dry, and the refiduum became 

 quite black. A little fulphurie acid was dropped on this 

 black matter, by which it effervefced ftrongly, and very 

 pungent fumes arofc which had ail the properties of muri- 

 atic acid. 



[To be concluded in the next Number ] 



VII. Method employed between Melun and Lieufaint in France, 

 to meafufe the Bafe of a Triangle, in order to determine 

 the Length of an Arc of the Meridian. From the Journal 

 de Phyfique, 1798. 



X HE high road between Lieufaint and Melun has lately 

 been the theatre of an operation extremely interefting, which 

 will form an epoch in the hiftory of the fciences. In" order 



to 



