CAR

CAR

( 262 )

and oil which would otherwife be diflipated inthe air, are colle£ted; the watery acid partbeing then feparated from the other is evapo-rated to drynefs, and the refiduum by calcina-tion affords an alh extremely rich in alkali.

Potalh is converted into a much purer alkalinefait called pearl-afi !>, by calcination : for this pur-pofe, the potafh broken into moderately fmallpieces, is fpread on the floor of a reverberatoryfurnace, and being then kept red-hot, but notmelted, for an hour or two, ftirring it occafion-ally with an iron rake, all the carbonaceous andcolouring particles are burnt out, and thereremains behind a dry porous and confiderablycauftic fait, extremely deliquefcent, and fromits bluifh white colour called pearlafh.

It has been thought of confequence in aneconomical point of view to difcover the pro-'

portion of potafh afforded by different vegetables,and many analyfes have been made for this pur-pofe. They are however for the molt partunfatisfactory, as they indicate only the quan-tity of foluble faline ingredients without diftin-guifhing the carbonated potafh from the fulphatand muriat of potafh with which it is alwaysmixed; The moft remarkable and intereftingrefults will be found in the following table,part of which were afcertained by a Com-mittee of the Academy of Sciences at Paris,and the reft by the chemifts whofe names arefubjoined. ioo parts of each different fpecies,being previoufly thoroughly dried, were burnedby an open fire to allies, which, after beingweighed, were accurately lixiviated till all theirfaline contents were extracted,.

ioo parts

Afhes

Salt

Salt from

100 parts of

Afhes

Fumitory

21.9

7-9

3<5-

Wiegleb

Wormwood

9.74

7-3

74.8

Ditto

Common Nettle

10.67

*•5,

23-4

Pertuis

Sow Thiftle (Sonchus arvens.)

10.5

1.96

18.6

Ditto

Fern

5-

0.62

12.5

Ditto

Ditto

3- 6 4

©42

11.6

Home

Stalks of Maize

8.86

i-75

2;.

*9-7

Ditto Sunflower

5.72.

34-9

Buckwheat

33-3

Vauquelin

Vine branches

3-4

0.55

16.2

Heath

114

Wildenheim

Foxglove (digitalis purpurea)

33-

Leipfic econ. Soc.

Celandine (Chelidonium maj.)

25..

Ditto

Nightfhade (atropa bellad.)

27.

Ditto

Boxwood

2.9

0.22

7.8.

Sallow

2.8

0.28

10.2

Elm

2-3

°-39

16.6

Oak

i-3

0.15

11.1

Beech

0.58

0.12

21.9

Afpen

1.22

0.07

6.1

Fir

o-34

0.04

13.2

Upon a curfory infpef/tion of this table, itappears that the fucculent herbaceous plantsafford a prodigioufly greater proportion both ofallies and fait than the fhrubby and ligneousones: it is however to be obferved, that theywere all reduced to a ftate of perfect drynefsbefore being weighed, a circumftance whichwill in a confiderable degree account for the ap-parently greater quantity of fait contained in thefucculent vegetables; for while the differentkinds of wood will not lofe more than or even

\ of their weight in drying, fumitory will prowbably lofe T %- or even more. It is not likelytherefore that it can be ever worth while, asfome fpeculators have propofed, to be at the ex-pence of cultivating fumitory and wormwood,for the fake of the potafh contained in theirafhes.

It has been a fubjedl of enquiry among che-mifts whether the potafh that is obtained by thecombuftion of vegetables is formed by this pro-■ cefs, or only difengaged by the decompofftion of