C H E M I S T R V. 



129 





i proper. 



Comprxt- 

 tion of oak 



bn cxaTnir.eJ. Sulphuric acid likewise chars it. Oxy- 

 :ic acid gas bleaches it, and probably alters and dis. 



r phcd in a concentrated state. 



Ctl " i; i xtremely combustible, and burns with a 



.ively Bame. The ashes left behind, according to 



'.nil, contain some potash. When distilled, it 



yields a great portion of acidulous water, and a small 



:ity of oil, but no ammonia, 



S-rr. XXIX. Of Subcr. 



This nsme has been introduced into chemistry by 

 ,:roy, U> denote the outer bark of the quercus su- 

 r the common cork ; a substance which possesses 

 propertied different from all other vegetable bodies. 



It is exceedingly light, soft, and elastic; very com- 

 bustible, burning with a bright white flame, and leaving 

 a %ht black bulky charcoal; and when distilled, it yields 



ammonia. 



When digested in water, a yellowish coloured solu- 

 tion is obtained, seemingly containing extractive, as near- 

 ly the same proportion is taken up by alcohol. Sulphu- 

 ric acid readily chars it. Nitric acid gives it a yellow co- 

 lour, corrodes, dissolves, and decomposes it ; converting 

 it partly iuU> suberic acid, partly into a substance re- 

 n wax, partly into artificial tannin, and partly 

 into a kind of .starchy matter. i 



SECT. XXX. Of Wood. 



All trees, and most other plants, contain a particular 

 subftar.i. c, well known by the name of mood. If a piece 

 of wood b? well dried, and digested, first in a sufficient 

 quantity of water, and then of alcohol, to extract from 

 i: all the substances soluble in these liquids, there remains 

 only behind the icooily Jtfirf. 



'\ his substance, which constitutes the basis of wood, 

 is composed of longitudinal fibres, and is easily subdivided 

 JLto a number of smaller fibre. It is somewhat tran- 

 sparent ; is perfectly tasteless ; has no smell ; and is not 

 altered by exposure to the atmosphere. 



It is insoluble in water and in alcohol. The fixed al- 

 kalies, when assisted by heat, give it a deep brown co- 

 lour, render it soft, and decompose it. A weak alka- 

 line solution dissolves it without alteration ; and it may 

 bf thrown down again by means of an acid. By this 

 property we are enabled to separate wood from most of 

 the other vegetable principles, as few of them are solu- 

 ble in weak alkaline leys. 



\Vhcn heatrd, it blackens without melting or frothing 

 up, and exhales a disagreeable acrid fume, and leaves a 

 charcoal which retains exactly the form of the original 

 mass. When distilled in a retort, it yields an acid liquor 

 of a peculiar taste and smell, distinguished by the name 

 of pyrohgnous, and formerly considered as a distinct 

 acid ; but fr ourcroy and Vauquelin have lately ascertained 

 that it is merely the acetic acid combined with an empy- 

 reumatic oil. 



Thenard ar.'l Gay-Lussac found the constituents of oa-k, 

 Oxygen, - - - 4J.7H 

 Carbon, - - - .02.53 

 Hydrugen, - - 5.69 



100 



The constituent! of beech they found to be 

 Oxygen, . . . -K2.73 

 Carbon, - - - 51.45 

 Hydrogen, . - - 5.82 



SECT. XXXI. OfAUhilu's, 



Chemical 



r.>. 



t''u.l in 1 



The only alkalies found in plants are potash, and soda, 

 Ammonia may indeed be obtained by distilling many ve- AU 

 getable substances, but it is produced during the opera- found ia 

 tion. One or other of these alkalies is found in every 

 pla.it which has hitherto been examined. The quantity 

 indeed is usually very small. From the experiments of 

 Vauquelin, it is probable that the alkalies are combined 

 in plants with acetic and carbonic acids. 



1. Potash is found in almost all plants which grow at I'otasli. 

 a c'.istance from the sea. It may be extracted by burn- . 

 ing the vegetable, washing the ashes in water, filtrating 

 the water, and evaporating it to dry-ness. It is in this 

 manner that all tlu- potash of commerce is procured. 



In general, three times as much ashes are obtained 

 from shrubs, and five times as much from herbs, as from 

 trees. Eqinl weights of the branches of trees produce 

 more ashes than the trunk, and the leaves more than the 

 branches. Herbs arrived at maturity produce more ashes 

 than at any other time. Green vegetables produce more 

 ashes than dry. 



'2. Soda is found in almost all the plants which grow Soda. 

 in the sea, and in many of those which grow on the 

 shore. In general, the quantity of soda which plants 

 contain bears a much greater proportion to their weight 

 than the potash does which is found in inland vegetables. 

 100 parts of the salsola soda, for instance, yield 19-921 

 of ashes ; and these contain 1.992 parts of soda; some 

 <it which, however, is combined with muriatic acid. 

 The plants from which the greater part of the soda, or 

 barilha as it is called, which is imported from Spain, is 

 extracted, are the salsola saliva and vermiculata. 



SECT. XXXII. Of Earths. 



The only earths hitherto found in plants are the four Earth 

 following : Kme, silica, mognaia, alumina. found in 



1. Lime is usually the most abundant of the earths of plan's. 

 plants, and the most generally diffused over the vege- Lime, 

 table kingdom. Indeed it is a very uncommon thing to 



find a plant entirely destitute of lime : salsola soda is al- 

 most the only one in which we know for certain that this 

 earth does not exist. 



2. Silica exists also in many plants, particularly in Silica, 

 grasses and equisetums. Mr Davy has ascertained 



that it forms a part of the epidermis, or outer bark of 

 these plants ; and that in some of them almost the whole- 

 epidermis is silica. 



3. Magnesia does not exist so generally in the vege- \j a?n( , s jj| 

 table kingdom as the two preceding earths. It has been 



found, however, in considerable quantities in several sea 

 plants, especially fuci ; but the saisola soda contains a 

 greater proportion of magnesia than any plant hitherto 

 examined. Mr Vauquelin found that 100 parts of it 

 contained 17.929 of that earth. 



4. Alumina has only been found in very small quanti A!umina 

 ties in plants. 



The following Table exhibits tb.e quantity of earths 

 and metallic oxides in grains, obtained by Schrxder from 

 32 ounces of the seeds of the following kinds of corn ; 

 wheat (triiictim fiyberniim), rye (secale cereale), barley 

 rhorc/einn vulgarc"), oats (avfila fatii-a"), and likewise 

 from the same quantity of rye' straw. 



100 



VOL. TI. PAHT I. 



