t4-t On scvnal ihdigenous VJanfs ivhich viaj/ 



tlie dificrcncc that we establish between the plants that can 

 b(; used in tannino;. 



Those of the licst sort have no smell, or at most a verv* 

 •ne.ik one, but thev have a very sharp and astringent taste. 

 They eontain only the aetive and fixed prineiples which we 

 have mentioned, or at most an inconsiderable mixture of 

 Glco-intlanmiable parls^ which give a weak balsamic smell 

 to the watcrdistillcx:! from them j without any sharp or styptic 

 taste. The proportion of these parts varies in the terrco- 

 resinoso-o-ummy substance ; but that w hich connnonly 

 exists in the greatest part of the coriaceous plants is such, 

 that, for instance, in a pound of them the terreous parts 

 con^titute one-third, or even t)ne-half ; and the gummy 

 principle about one-fourth or one-third, and in some as 

 nuich as one-half, while the proportion of rosin is the 

 smallest of all, being onlv from twenty to fifty grains, or 

 at most a drachm and about twenty grains^ 



In the second sort of these plants we find^ indeed, the 

 ihove-mcntioned fixed active principles, but not in the 

 same proportion, beeause they are mixed with other prin- 

 ciples l)oth volatile and fixed, so as to constitute the smallei' 

 part of the whole compound. Besides the fixed parts there 

 exists m these substances an unctuous balsamic oleosa-) or 

 raporoso^'Spirit fiosn-t't lurcous princii)lc. The volatile parts 

 become stron disengaged from the rest, by the heat of the 

 tanning Ive, and evaporate, so that it is not at all times 

 possible to discover any specific remains of them in the 

 leather. 



If wc examine next what the fixed terreo-gvmtmj or 

 fcrrco-res/noso-gmiinii/ substance consists of, we shall ob- 

 tain a verv clear knowledge of it, either from considering 

 tlie manner in which it is naturally produced, or by means 

 uf chemical experiments. This terreous matter is some- 

 times coarser, sometimes finer, sometimes in a greater and 

 sometimes in a smaller quantitv ; audit contains an oily 

 STilistance, or inflammable principle, attached to a light 

 acid, of the nature of vegetable acid, but not caustic, like 

 mineral acid. In analysing the fixed substance of coria- 

 eeous plants, we get by the alembic, out of a pound medi* 

 cal weight, nearly the following parts, in a proportion 

 more or less different : I. About an ounce and two drachiiis 

 of a clear, empyreumatic, i)ut not astringent phlegm ; t?. 

 About two ounces and live drachms of an acid yellowish li- 

 quor; 3. An oimee and somewhat more than six drachms 

 ^f aa cmpsTCumatJc oil. The caput inorhimn often con- 

 stitute* 



