CHEMISTRY. 
declivities of their mountains, to form very productive 
nitre beds. The upper tide of thefe fquare flables refts 
on the mountain, while the lower is fupported by Hones 
or pillars of wood, railed two or three feet above the 
earth, according to the greater or lefs declivity. This 
leaves an interval open to the air between the floor of 
the itable and the mountain. In this place a ditch is 
dug of about three feet in depth. This ditch is filled 
with very porous earth, which imbibes the urine of the 
cattle. It is lixiviated every two or three years. The 
earthy refidue is dried in the open air, and returned back 
•into the ditch. In tbismanner they obtainabout a thoufand 
pounds of faltpetre from an ordinary itable at each lix- 
lyiation. 
The earthy part of nitre beds requires to be renewed 
mere or lefs frequently according to the quantity of cal¬ 
careous earth which it contains. Mo particular time can 
be ipecified for the term of putrefaction, the periods of 
moiftening the beds, or the time proper for turning them. 
The appearance of the beds, and the general principles 
already laid down, can only direCt thefe particular fteps, 
which mult vary extremely according to circumftances. 
The general marks by which a bed may be'known to 
contain io much nitre as to make it worth working, are 
the efflorefcence and cracks on the furface in which no 
plants grow. If fome of the particles of the bed be tail¬ 
ed, they will give a fait tafte, which will vary, however, 1 
according to the earthy or alkaline balls, and may there¬ 
fore be mild, acrid, or bitter. The bed rqufl be after¬ 
wards examined to the depth of feveral inches, and in 
different places, in order to alcertain whether the whole 
be nitrified. Another, but more troublefome method, 
is, to lixiviate a fmall quantity of the bed, a cubic foot, 
or yard, for'inftance, and from its produce to calculate 
the value of the whole. 
The following is the procefs now generally followed 
in the great manufactories in France, for the purification 
of nitre. The nitre is firfl pounded, and put into tubs 
in quantities of 500 or 600 pounds, Twenty per cent, of 
water is poured into each tub. The mixture is well ftir- 
red, and left to digefl for fix or feven hours, during 
which time the water acquires the denfity of between 
twenty-five and thirty-five degrees. This water is now 
poured off, and ten per cent, of frtfh water added, which 
is fuffered to remain only for one hour. Five per cent, 
of water is now to be poured on, and immediately drawn 
off as foon as it has been ftirred. The nitre, when pro¬ 
perly drained, is thrown into a boiler, containing fifty 
per cent, of boiling water. The folution will mark be¬ 
tween fixty-fix and fixty-eight degrees of the hydrome¬ 
ter. The folution is next poured into a veffel to cryflal- 
lize, where, in the courfe of from four to fix hours it 
depofits about two-thirds of the original quantity of ni¬ 
tre. As it is of confequence in the fubfequent drying 
that the cryflals fhould be in fmall needles, it becomes 
neceflary toftir the folution during the whole time of the 
depofition. The cryflals formed are removed with a 
fkimmer, and thrown into baflcets to drain, and the wa¬ 
ter which paffes through is carefully colleCled. The lalt- 
petre is afterwards put into wooden veflels with double 
bottoms, formed in the fliape of mill-hoppers. The up¬ 
per bottom, which is railed about two inches above the 
, other, is perforated with a number of fmall holes, through 
which the water palfes to the lower bottom, from which 
it is difeharged by a fmgle opefling. The faltpetre is 
wafhed in thefe veflels with five percent, of water; and 
this water is afterwards employed in the folution of the 
fait. This faltpetre, well drained and expofed for fome 
hours to the air upon drying tables, is fit to be ufed for 
the manufacture of gun-powder. This fait may be. dried 
more quickly by a Hove, or by putting it in a flat metal¬ 
lic veffel. For this purpofe, it may be put into the vef¬ 
fel to the depth of five or fix inches, and heated to about 
13 5 0 of Fahrenheit. By ftirring it in this fituation for 
two or three hours, it lofes its regular form, and puts 
Vom lV. No. 193. 
241 
on the appearance of a fine dry fand. This degree of 
drynefs, however, is not neceflary when the gun-powder 
is made by pounding. Thefe difeoveries, which refulted 
from the neceflities the French were lately under, ofiup- 
plying their powder-mills with falt-petre of their own 
making, cannot fail to prove of great value to this coun¬ 
try, when ever it might happen to be cutoff, as they were, 
from foreign fupplies of nitre. 
Nitrat of Soda.— This fait is feldom found pure in 
nature; it is therefore produced by art. Bowles aflerts 
that he found it in Spain. It is called cubic, quadran¬ 
gular, or rhomboidal, nitre: Fourcroy fays, that rhotn- 
boidai is the propereft name, becaufe that is generally the 
fliape of the cryflals. 
This nitrat is prepared with cafbonat 'of foda : -it is to 
be faturated with nitric acid ; ftrain the liquor, then eva¬ 
porate with a gentle heat, till pellicles are formed on the 
furface: when left to fettle and cool, rhomboidal cryf- 
tals or prifms are formed. Its tafle is cooling, arid.ra¬ 
ther more bitter than that of nitrat of potafh. Fire de- 
cl[m poles it; but it decrepitates, and does not melt fo 
eafily as the nitrat of potafli; but, like that fait, it gives 
out vital air, mixed with azotic gas,"at the fame time 
that it becomes alkalized. It is fiightly deliquefeent 
when expofed to the air. Nitrat of foda detonates on coals, 
and caufes the complete combuftjon of inflammable bo¬ 
dies ; if it is heated, the detonation is fomewhat lefs ra¬ 
pid than that of nitrat of potafli, and the colour of the 
flame is a deep yellow ; that of nitrat of potafh is a very 
bright vivid -red ; and this may ferve to fliew whether 
there be nitrat of foda in faltpetre or not. Gunpowder 
made with nitrat of foda will not have the fame flrength, 
nor give fuch a loud report, as that made with nitrat of 
potalh. After combnllion, there remains potafli or loda 
combined with carbonic acid, which proves that all the 
carbonic acid which is formed does not exhale. This, 
fait is eafily loluble in water; it requires about three 
parts of water of the mean temperature of the atmofphere 
to diflblve it: boiling water diffolves more than its weight. 
The fulphuric acid decompofes nitrat of foda; white 
vapours are thrown off, and fulphat of foda is formed. 
Muriatic acid decompofes nitrat of foda, but not by 
feizing on the foda: it attacks the nitric acid, makes 
nitrous acid, and a muviat of foda is formed. Much.of 
the muriatic acid is required ; for, while one part of it 
decompofes the nitric acid, the reft combines with the 
1 'oda. With nitrat of foda and muriatic acid, a kind of 
nitro-muriatic acid is formed. 
A very good glafs is made with nitrat of foda and fine 
fand. The foda unites with the filex, the nitric acid is 
decompofed by the caloric, and in the crucible remains 
a very beautiful and pure glafs, finely than can be made 
with nitrat of potafli. Nitrat of loda is decompofed by ba- 
ryttes and potafli, forming nitrat of barytes or nitrat of 
potafh, as the cafe may be. 
Nitrat of foda may be applied to the fame ufes as nitrat 
of potafli; but as it does not produce all the effefts of this 
lall fait (doubtlefs on account of its greater affinity with 
water), and likewife becaufe it is merely a produ6t of art, 
little ufe has yet been made of it, neither have all the 
experiments been made, which are neceflary to ailord a 
complete knowledge of its properties. 
Nitrat of Strontian. —This is obtained by de- 
compofing fulphure of llrontian with nitric acid. It 
cryftallizes in oftahedrals. Subjefted to heat in a cru¬ 
cible, it is entirely decompofed, and the earth remains 
pure at the bottom of the veffel. By putting a little ni¬ 
trat of llrontian in the wick of a taper, it gives a purplifh 
cad to the flame. By burning alcohol, which will hold 
this nitrat in folution, the fame kind of flame is pro¬ 
duced ; which particularly diftinguifhes this earth from 
barytes, 
A mixture of nitrat of llrontian, of fulphur, and of 
charcoal, in the fame proportion as thefe latter fubllances 
are ufed for making gunpowder, though very dry, burns 
3 flowly. 
