NIT

NIT

( 163 )

The cfflorefced furface to the depth of three inches, of the fame cave, afforded

without'

[Nitre -------

lbs. oz.

* — 5

gTOS.

— 7

grains.

3 1

Potafhwith j

[ Mother water, which gave[Nitre -------

3 — 1

— 3

— 2,4

Potafh J

| Muriat of Potafh - - -

O - 12

— 6

— 66

5—4

— i

— 49

A fpecimen from another {hallow cave, after the outer furface to the depth of between threeand four inches had been removed, afforded from ioo lbs.

without 1

[Nitre -------

lbs.o —

oz.

8

gros.

— o

grains,

— o

Potafh jwith

[ M other water, which gave[Nitre -------

i —

9

— 4

— 8

Potafh ^

f Muriat of potafh - - -

o —

5

— 4

— 5*1

2 — 7 — ° — 59 r

Hence it appears that the chalk cornpofingthefe rocks, though perhaps not abfolutely andentirely deftitute of nitric ,ickl even at theircentre, is much more abundant in this fubftancein proportion as it is fituated near their furface,and that the perfect nitre or nitrat of potafh isonly found near the furface of the chalk : acircumftarice which feems to fhow that boththe acid and alkali have been either depofitedfrom the air, or formed by the contaft of thislatter with the chalk. In confirmation of thisdeduction may be mentioned an experiment bythe Due do la Rochefoucault, who lixiviated aconfiderable quantity of chalk, fo as to dilfolveout its faline contents, and then expofed it tothe adfion of the air for fourteen months,during which period it had acquired not onlynitric acid but potafh, fince the liquor of thefecond lixiviation depofited by evaporation alittle nitre, and afterwards a confiderable quan-tity more on the addition of potafh. Thefefa£ts having never been called in queftion, thenext inquiry that occurs is whether the atmof-phere furnilhes the entire nitric acid or onlyone of the conflituent parts of it ? That thislatter is the cafe might be inferred from thefrequent occurrence of organic remains andtmpieflions in chalk, whence this mineral maybe fuppofed to be by no means deftitute ofanimal, matter. Againft this however there maybe alleged a direa experiment by M.Thouvenel,7 on ex P°fing fome waflied chalk for fix oreven months to a portion of atmofpheric airCOn / f n , ed .’ n ^ large receiver, and previoufly wellviajhed *n dtfhded water, found that not an

atom of nitrat of lime was generated ; while ina fimilar experiment in which waflied chalkwas expofed to unwa/hed air, a very fenfiblequantity of nitrated lime was produced. Nowthe wafhing could not feparate the azot oroxygen, though it might and no doubt wouldtake away any nitric acid ready formed, orany nitrous fait that might be contained in theatmofphere. It is obferved of thefe chalk rocksthat thofe parts that are adjacent to inhabitedbuildings yield a greater proportion of nitrat ofpotajh than thofe which are at a diflance fromhoufes; a circumftance that feems to point outa probable fource of the alkali without fuppofingit to be generated either in the air or chalk.It is well known that the common fuel in France is wood, therefore the air in the vicinity ofhoufes muft be - more or lefs impregnated withpyroligneous acid contained in the wood fmoke;but the acid vapour that flies off in the com-mon method of preparing charcoal (and whichis no other than pyroligneous acid) when col-le&ed in a proper apparatus condenfes into afour liquid from which by gentle evaporationa black refidue is procured that yields by incin-eration a large proportion of potafh, as we havefhewn in our account of that fubftance, in thearticle Car bon at of Potash .

It only remains to give an account of theextraction of nitre from the earths in which itis contained, and of the purification of thisfait.

The fir ft thing is to allay the earth. Thisis done by lixiviating a few pounds of it, andadding to the liquor thus obtained as muchX 2