240 C H E M ] 
decompofed- Herbiveyous are in general preferred to 
carniverous animals. Worms, infeCts, and reptiles, are 
laid to be capable of being refolved almoft entirely into 
nitre. Blood feems to be the animal fluid which affords 
the greateft quantity of this fubftance. The dung of hens 
and pigeons has always been conlidered as extremely pro- 
dudtive. That of oxen is faid to yield lefs than that of 
flieep. Urine ought to be employed only towards the 
latter ftage of the procefs of nitrification, as it favours 
the produdlion of muriat of i'oda. The purpofe which 
thele animal and vegetable fubftances ferve in nitrifica¬ 
tion is now known. They all give out, during their de- 
compofition, a greater or lefs quantity of azot, which, 
uniting with the oxygen of the atmolphere, forms the 
nitric acid. But the prefence of lime, or of fome alkaline 
bafis, is neceflary to fix this acid. When vegetable or 
animal bodies are mixed with filiceous or aluminous 
earths, little or no nitric is produced; the acid which is 
faid to be formed being either exhaled into the air, or 
carried off by the water. The addition of an alkaline 
fubftance is proper only towards the end of the procefs; 
if added fooner, it retards the decompofition of the or¬ 
ganic fubftance. 
The lighted and moft porous calcareous fubftances are 
found to anfwer beft. Their property of affording nitre 
is increafed by their containing a quantity of iron : it is 
increafed alfo by dividing them minutely, foas to increafe 
as much as poflible the extent of their l'urface. It feems 
to be for the fame reafon that calcareous fubftances which 
contain an admixture of filiceous or aluminous earth, 
or even of chaff, are more productive than the calcareous 
earths which are pure. It is not eafy to determine nor 
to preferve the juft proportion between the earthy bafe 
and the putrifying principles ; it muft be fucb, however, 
that all the acid formed may be readily combined. Too 
great a proportion of earth is hurtful, not only by its 
occupying an ufelefs fpace, but alfo by retarding putre¬ 
faction. In general (Chaptal fays), the proportion of 
calcareous earth may vary from one-fifth to one-tenth of 
the volume of the vegetables employed. Befides ferving 
as a bafe to fix the acid, do not calcareous fubftances 
difpofe the oxygen and the azot to unite, in confequence 
of the affinUe difpofe? 
The oxygen gas combines with azot only in the mo¬ 
ment of its dilengagement from animal or vegetable 
matters, and before it has affumed the gafeous form. In 
this date it has been hot unaptly termed Nafce/it azotic 
gas. A high degree of temperature becomes, therefore, 
improper, becaufe it would caufe the azot to aflume the 
gafeous form, and would confequently prevent the for¬ 
mation of the acid. A very low temperature is equally 
injurious, becaufe, by retarding or putting an entire flop 
to the decompofition, it prevents the dilengagement of 
azotic gas. Experience has fhewn, that the temperature 
fitted: for the production of nitre lies between 75 0 and 
90 0 of Fahrenheit. This temperature muft refult from 
the decompofition of the animal and vegetable fubftances, 
and not be merely the effeCl of art. It is to be preferved 
by excluding carefully currents of cold air, which would 
tend to carry off the heat. 
An intenfe or ltrong light feems to be very injurious 
to the production of nitre. Befides the effeCt which it 
will undoubtedly have of volatilizing the azot, it may 
fairly be queftioned, whether it will not alfo decompole 
the nitric acid. Saltpetre-makers, aware of the pernicious 
tendency of too ltrong light, have generally chofen a 
northern expofure for their nitre beds. This expofure 
has the additional advantage of preferving a more equal 
temperature. Towards the latter ftage of the decompo¬ 
fition, it has been found ufeful to expofe the putrifying 
matters to the light. At this period it feems to give new 
energy to the procefs, and to promote greatly the pro- 
duCticn of nitre. 
In order to produce the combination of the oxygen 
gas with the azot, it is neceflary that thefe two fubftances 
S T R Y. 
fheuld remain for fome time in contaCt with each other,, 
All currents of air muft, therefore, be unfavourable to 
the production of nitre; and hence it is that we find 
faltpetre-makers recommend, that the air fhould be in a 
Hate of abfolute reft or ftagnation. I11 order to increafe 
the furface expofed to the air, it is a common practice 
with fome faltpetre-makers to fix flakes of wood in various 
directions in the nitre beds. After the niafs has become 
dry and a little firm, thefe flakes are withdrawn, that the 
air may penetrate every part of the mafs, and come into 
contaCt with as large a furface as poflible. The propriety 
of occafionally renewing this air muft be obvious to every 
one who reflects, that this is the fource from which the 
oxygenous part of the nitre is derived. It becomes ne- 
ceflary alfo, particularly in the latter periods of the pro¬ 
cefs, to ftir the mafs, and expofe every part of it to the 
aCtion of the air. Great caution is required not to do 
this either too early or too often, as it is apt to retard 
putrefaction. 
Either too great or too finall a degree of moifture is 
equally unfavourable to the formation of nitre. In a hot 
and dry atmofphere, the parts of vegetables and animals 
would be diflipated without undergoing the procefs of 
putrefaction. Too much moifture, on the contrary, might 
not only retard the putrefaction, but might alfo carry 
off the acid after it had been formed. Great caution, 
therefore, is neceflary in watering the nitre beds. The 
liquids moft proper for this purpofe are, the blood of ani¬ 
mals, either by itfelf, or diluted in water, the water from 
dunghills, fewers, &c. Thefe, befides affording the ne- 
ceffary degree of moifture, contain much vegetable and 
animal matter', in a flate highly favourable to the produc¬ 
tion of nitre. 
Such are the general principles on which nitre beds 
are conftruCted; but the particular Heps of the procefs 
vary in different countries. Thefe will be belt underftood 
by examples. 
In Prufiia, five meafures of black vegetable earth, or 
the earth of fubterranean caverns, are mixed with one 
meafure of unlixiviated allies and fome ftraw. Thefe fub¬ 
ftances beat up with the water of dunghills or fewers, are 
formed into walls or beds of twenty feet long, fix or fe- 
ven feet high, and three feet broad at the bale, declining 
to two at the top. Thefe beds are contained in (hallow 
wooden cafes or moulds, and are covered with a thatch 
of ftraw to proteCl them from the rain. They are moif- 
tened from time to time, and are fit for being lixiviated 
at the end of a year. 
In Malta, they employ the moft porous calcareous 
earth mixed with ftraw, which has been lixiviated, Ob¬ 
long triangular piles are formed of alternated layers, each 
half a foot in thicknefs, of this earth and dung. Thefe 
layers are terminated by a very thin layer of dung, ap¬ 
plied loofely with the hand. The bed is occafionally 
fprinkled with mother water of faltpetre, urine, and wa¬ 
ter from dunghills. As foon as the furface becomes dry, 
it is turned down, and the bed moiftened. This becomes 
fit for lixiviation at the end of three years. During the 
firft year, the beds are every month lprinkled over with 
the powder of flacked lime. 
In Sweden, their beds are railed on bricks laid on the 
earth. On this' bafis is placed a layer of mortar, com- 
pofed of meadow turf, allies, lime, and the neceflary 
quantity of mother water, or of urine. ' Over this is 
placed a layer of ftraw; and thefe layers of ftraw and 
mortar are continued alternately to the fiummit. The 
beds are defended from the rain, and moiftened occa¬ 
fionally with urine, ftagnant water, &c. Thefe beds yield 
nitre at the end of a year, and laft for ten years. The 
faltpetre is fwept off every eight days; and, after each 
fwe.eping, the beds are moiftened with weak mother wa¬ 
ter. The matter remaining at the end of ten years forms 
an excellent manure in the culture of hemp and flax. 
In the canton of Apenzel, in Swiflerland, they take 
advantage of the fituation of their (tables, on the rapid 
declivities 
