•HO On several indigenous Plants whicli ma?J 



oxyscn jras was observed^ and the whitisJi-grav colour of" 

 the whole mass was changed to a blackish red. The opera- 

 tion was then suspended ; and, on cooling, the whole mass 

 exhibited tlu'oughout that uniform red colour observed in 

 red precipitate, when reduced to a state of the greatest 

 lincness; and it was so much divided that it could be shaken 

 from the retort without breaking it. No traces of metallic 

 quicksilver remained, but a small quantity of acid fluid; 

 which induced me to repeat the experiment with a larger 

 quantity of mercury. I therefore took 400 parts of quick- 

 silver, which were dissolved as before in nitric acid : when 

 the solution was evaporated to drvness, it was mixed with 

 400 parts more of metallic quicksilver, and the mixture 

 was treated as before. Except tiie dlifercnce jn the weight, 

 the results of this operation were not diflerent from the 

 preceding. 



This method not only saves one half of the nitric acid, 

 but the retort can be several times used for the same pur- 

 pose. The tedious process of preparing precipitate is also 

 avoided, as it is soon obtained in the form of a very fine 

 powder. The loss of tiiTje and of fire is also much less, a» 

 scv'cral pounds of white mercurial paste can be converted 

 into red oxide in less than thirty minutes. I subjected to 

 experiment, however, onlv a few ounces, and the opera- 

 tion was always finished in from three to five minutes irj, 

 a sudden heat. On this account the present method is 

 highly worthy the attention of chemists and apothecaries. 



XXI. AMewoir cniicc-rnhig several Indigetinvs Pimits, which 

 may strrve as a Sulstifule for Otik Bark, and for tort am 

 foreign Articles in the Tunning tf lAiathvr'''. 



JL HE object of this memoir is to show how the destruction 

 of trees, and particularly of oak-trees, which are so valu- 

 able, mav in great part be preventi^d. A great consumption 

 of them is caused by the tanneries. A discovery has been 

 made last summer, which will contribute to the preservation 

 of the trees, and to the contiriuation and even to the in- 

 crease of the tanneries. Eight new sorts of leather hav-e 

 been prepared and tanried witho\it any bark at all, and with 

 materials of which we shall give a detailed account. By 

 vising these articles, there is a saving, not onlv of bark, 

 but likewise of several foreign drugs, which are generally 



• Frdin the tenth volume of the Tuiiisuitions of tbe Ryal Acaefevty of 

 BoJpi. 



V.sc4 



