books, are much to be pitied. As they are debar-
red the free ufe of air and exercife, this I will ven-
ture to recommend as the beft fuccedaneum to both.
Though it were to be wifhed, that modern fcholars
would, like the ancients, meditate and converse
more in walks and gardens and open air, which,
upon the whole, would perhaps be no hindrance to
their learning, and a great advantage to their
health. My own fedentary course of life had long
fince thrown me into an ill habit, attended with ma-
ny ailments, particularly a nervous cholic, which
rendered my life a burthen, and the more fo, be-
cause my pains were exafperated by exercise. But
fince the ufe of tar-water, I find, though not a per-
fect
recovery from my old and rooted illness, yet
fuch a gradual return of health and ease, that I
efteem my having taken this medicine the greatest
of all temporal bleffings, and am convinced that,
under providence, I owe my life to it.

120. In the diftilling of turpentine and other balfams by a gentle heat, it hath been obferved, that there rifeth firft an acid fpirit (n) that will mix with water; which fpirit, except the fire be very gentle, is loft. This grateful acid fpirit that firft comes over, is, as a learned chemift and phyfician informs us, highly refrigeratory, diuretic, fudorific, balfamic or prefervative from putrefaction, excellent in nephritic cafes, and for quenching thirst, all which virtues are contained in the cold infufion, which draws forth from tar only it's fine flower or quinteffence, if I may fo fay, or the native vegetable fpirit, together with a little volatile oil.

121. The diftinguifhing principle of all vegetables, that whereon their peculiar fmell, tafte, and fpecific properties depend, feems to be fome

(n) 7.

1

extremely fine and fubtile fpirit, whofe vehicle is an exceeding thin volatile of itself detained in a groffer and more fin or balfam,. lodged in proper cells in and feeds, and most abounding in autur ter, after the crude juices have been concocted, ripened, and impregnated light. The fpirit itfelf is by fome be an oil highly fubtilized, fo as to water. But fuch volatile oil is not but only it's vehicle. Since aromatio ing long expofed to air, will lofe th fmell and tafte, which fly off with th vegetable falt, without any fenfible din the oil.

122. Those volatile falts, that are f raifed by a gentle heat, may juftly b effential (a), and to have pre-existed getable; whereas the lixivial fixed fal by the incineration of the fubject, wh conftituent parts have been altered or d the extreme force of fire, are by late upon very good grounds, fuppofed n pre-exifted therein; all fuch falts appea the experiments of fignor Redi, not the virtues of the refpective vegetabl and to be alike purgative and in a gree, whatsoever may be the shape of whether sharp or obtufe. But althou lixivious falts may not contain the o perties of the fubject; yet volatile falts flight heat from vegetables are allowed their native virtues: and fuch falts are bibed by water.

123. The moft volatile of the fal moft attenuated part of the oil, may (a) B.

Tate

h is

re

Dark

win

ghly folar ed to with

fpirit,

,be

pecific

irit of tion of

ree and

uppofed

the ve obtained natural oyed by chemifts, to have g, from preferve dubjects;

equal de

eir points,

fixed or inal proaifed by a preferve

adily im

and the

fuppofed

the

the firft and readieft to impregnate a cold infu fion (b). And this will affift us to account for the virtues of tar-water. That volatile acid in vegetables, which refifts putrefraction, and is their great prefervative, is detained in a fubtile oil mifcible with water, which oil is itself imprisoned in the refin or groffer part of the tar, from which it is easily fet free and obtained pure by cold wa

ter.

124. The mild native acids are obferved more kindly to work upon, and more thoroughly to diffolve, metallic bodies, than the ftrongeft acid fpirits produced by a vehement fire; and it may be fufpected, they have the fame advantage as a medicine. And as no acid, by the obfervation of fome of the best chemifts, can be obtained from the fubftance of animals thoroughly affimilated, it fhould follow, that the acids received into a healthy body must be quite fubdued and changed by the vital powers: but it is easier to fubdue and affimilate (e) the gentler than the stronger acids.

125. I am very fenfible, that on fuch fubjects arguments fall fhort of evidence and that mine fall fhort even of what they might have been, if I enjoyed better health, or thofe opportunities of a learned commerce, from which I am cut off in this remote corner. I fhall nevertheless go on as I have begun, and proceed by reafon, by conjecture, and by authority, to caft the beft light I can on the obfcure paths that lie in my way.

126. Sir Ifaac Newton, Boerhaave, and Homberg are all agreed, that the acid is a fine fubtile fubftance, pervading the whole terraqueous globe; which produceth divers kinds of bodies, as it is united to different fubjects. This according to (b) 1, 7: (e) 48

2

Homberg

1

Homberg is the pure falt, falt the prin felf fimilar and uniform, but never fo And although this principle be called the earth, yet it fhould feem it may perly be called the falt of the air, turned up and lying fallow receives air. And it fhould feem that this is principle of vegetation, derived into from all forts of manures, as well as air. The acid is allowed to be the ca mentation in all fermented liquors. fore, may it not be supposed to fermen and to conftitute that fine penetrating which introduces and affimilates the foo and is fo fugitive as to escape all the and perquifitions of the moft nice obfer 127. It is the doctrine of Sir If and Monfieur Homberg, that, as the is that which renders falt foluble in wa that fame which joined to the earthy p anfalt. Let it therefore be confidered organs (d) of plants are tubes, the folding, and diftending whereof by li conftitute what is called the vegetation of the plant. But earth itself is no water, fo as to form one vegetable with. Therefore the particles of ear joined with a watry acid, that is, th come falts in order to diffolve in wat in the form of a vegetable juice, the through the ftrainers and tubes of t the body of the plant, fwelling and it's parts and organs, that is, increafin Therefore the vegetable matter of the effect earth changed into falt. And to (d) 30, 31, 35.

t

2.

of

0

th

he

-eat

arth

the

fer

here

arth,

iple,

lants,
ations

ewton

y acid

To it is
makes it
at the
g, un-
s, doth

growth

Juble in
d there
must be
muft be

that fo,
may pafs

root into

Hiftending it's bulk. arth is in nder earth

fertile

fertile, is to caufe many of it's particles to affume a faline form.

f

128. Hence it is obferved, there are more falts in the root than in the bark, more falts in vegetables during the fpring, than in the autumn or winter, the crude faline juices being in the fummer months partly evaporated, and partly ripened by the action and mixture of light. Hence alfo it appears, why the dividing of earth, fo as to enlarge it's furface, whereby it may admit more acid from the air, is of fuch ufe in, promoting vegetation: And why afhes, lime, and burnt clay are found fo profitable manures, fire being in reality the acid, as is proved in the fequel (a). Marls alfo and fhells are useful, forafmuch as thofe alcaline bodies attract the acid, and raise an effervefcence with it, thereby promoting a fermentation in the glebe. The excrements of animals and putrid vegetables do in like manner contribute to vegetation, by increafing the falts of the earth. And where fallows are well broken, and lye long to receive the acid of the air into all their parts; this alone will be fufficient to change many terrene particles into falts, and confequently render them foluble in water, and therefore fit aliment for vegetables.

129. The acid, faith Homberg, is always join ed to fome fulphur, which determines it to this or that fpecies, producing different falts, as it is the vegetable, bituminous, or metallique fulphur. Even the alcaline, whether volatile or lixivial falts, are fuppofed to be nothing but this fame acid ftrictly detained by oil and earth, in fpight of the extreme force of fire, which lodgeth in them, without being able to diflodge fome remains of the

acid.

(a) 202.

130. Salts,