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piastres, the profit is 6% per cent.; and it rises to seven per cent. when the produce of the mines is still greater, as was the case during

/the -last twenty Tyears. We shall afterwards

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see that the mint of Mexico, and the house of separation (maison du depart), make an annual profit, of nearly eight -millions of francs.‘ ~

‘. The house of separation (casa del apartado) in which is carried on the separation of the gold and the silver, proceeding from the ingots of auriferous silver, formerly belonged to the family of the Marquis de Fagoaga. This important establishment was only annexed to the crown in 1779. The building is very small and very old; and it has latterly been rebuilt, in part, at a greater expence to the government than if its place had been supplied by a. new house, not situated in the middle of the town, and in which the acid vapours would have been better directed. Several persons interested in the works of the apartado remaining in their present situation, maintain that the vapours of nitrous acid which are diffused through the most populous quarters of the town, serve to decompose the miasmata of the surrounding lakes and marshes. These

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484 POLITICAL ESSAY ON THE [BOOK v.

ideas met with a favourable reception after acid
fumigations were used in the hospitals of the
Havannah and Vera Cruz.

The casa del apartado contains three sorts
of works, which are destined, 1st, to the ma-
nufacture of glass; 2nd, to the preparation of
nitrous acid; and 3rd, to the separation of the
-gold and the silver. The processes used in
these different works, are as imperfect as the

-construction of the glass-work furnaces, used

for the manufacture of retorts, and the distil-
lation of aqua fortis. The substance of the
glass (pasteladura) is composed of 0.46 of
quartz, taken from the veins of Tlapujahua,
and 0.544 of soda, which the Indians of Xalto-
ean and the Pefiol procure from the inciner-
ation of the Sesuvium portulacastru-m of se-
veral new species of Chenopodium, Atriplex,
and Gratiola, which will be‘ described in the
_Flora Mewicana of M. M. Sesse and Cervan-
tes, and of the Salsola soda of Europe, which
is cultivated in the valley of Mexico, both to
be eaten as a root, and to be reduced to
ashes. This soda of Xaltocan is mixed with

a good deal of sulphate V of potash and lime;

so that the carbonate of soda, which is every
where found in efilorescence in clay grounds,
would be much better adapted for the manu-
facture of glass. This pasteladura is not melted

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of a very refractive porphyritic rock, procured in a quarry in the vicinity of Pachuaca. More than 15,000 francs are annually consumed in the glass-house furnaces for wood. A retort costs nearly 14~ sous at the manufactory, and more than 50,000 are annually broken.

The nitrous acid used for the separation, is manufactured by decomposing raw saltpetre, by means of a vitriolic earth (coqaa) , which contains a mixture of alumine, sulphate of iron, and oxide of red iron. This colpa comes from the environs of Tula, where a mine is worked at the expence of the Farm of Colours.*' The saltpetre is furnished to the House of Separation, by the royal manufactory of powder. Each retort is charged with eight pounds of colpa, and the same number of pounds of nitrate of impure potash; the distillation lasts from thirty-six to forty hours. The furnaces are round, and unprovided with grates. The nitrous acid which is derived from the decomposition of as saltpetre p surcharged with muriate, necessarily contains much muriatic acid, which is carried off by adding nitrate of silver. We may judge of the enormous quantity of muriate of silver obtained in this establishment, if we Lreflect that there is purified a quantity of nitrous acid, suliicient

* Estanco real de tintes y colores.
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ver by "fire, melting it with small lead drops.
It would be more profitable, undoubtedly, to
make use, in the distillation of aqua fortis, of
refined, instead of raw saltpetre. They have
hitherto followed the slow and laborious me-
thod of purifying th_e acid by nitrate of silver,
because the royal establishment of the apar-
tado is under the necessity of buying the
saltpetre from the royal mamg"act02y of pow-
der and sallpetre, which will not give out
refined saltpetre, under 126 francs the quin-
tal. p

The separation of gold and of silver re-
duced to grains, for the sake of multiplying
the points of contact, takes place in glass re-
torts arranged in long- files on hoops, in galle-
ries from five to six metres in length.“‘ These
galleries are not heated by the same fire, but
two or three matrasses form as it were a se-
parate furnace. The gold which remains at
the bottom of the matrass, is cast into ingots
of fifty mares, while the nitrate of silver is
decomposed by fire during the distillation in
the retorts. This distillation, by which they
regain the nitre and acid, is also practised
in a gallery, and lasts -from 84~ to 90 hours.

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They are obliged to break theretorts to ob-
tain the reduced, and chrystallized silver. They
might no doubt be preserved, by precipitating
the silver by copper, but it would require ano-
ther operation to decompose the nitrate of
copper, which would succeed to the nitrate of
silver. At Mexico, the expence of separation,
is reckoned at from two to three reals de plata
(from 26 to 89 sous tournois) per marc of
gold.

It is surprising that none of the pupils of
the school of mines are employed either in
the mint, or in the casa del apartado ; and yet
these great establishments ought to expect use-
ful reforms, from availing themselves of mecha-
nical and chemical knowledge. The mint is
also situated in a quarter of the town, where
running water might be easily procured to put
in motion hydraulical wheels. All the ma-
chines are yet very far from the perfection which
they have recently attained in England and
in France. The ameliorations will be the more
advantageous, as the manufacture embraces
a prodigious quantity of gold and silver; for
the piastres coined at Mexico, may be consi-
dered as the materials which maintain the
activity of the greatest number of the mints
of Europe. 9

Not only working gold and silver, of which we have already spoken, has been improved

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