Mine ventilation in New Spain: foul air, a furnace draught and a royal article
A law book printed at Madrid in 1761 for the mines of New Spain turns from drainage to a second killer: the corrupt vapours the operarios must flee to avoid suffocating. It prints, with two figures, a furnace ventilator drawing the underground air out by a chimney, recommended because it spares the workmen the labour of bellows — and claims none of the invention as its own. In 1783 the crown made free ventilation a condition of every drainage adit.
Why this wins its question: Search for eighteenth-century mine ventilation and the answer that wins is British: Hales's ventilator, coal-pit furnaces, the Davy lamp coming later. The Spanish American side of it is invisible, and where colonial mining is discussed at all the working conditions appear only as an indictment. This entry puts the documents on the table instead. It quotes the 1761 Madrid commentary describing the corrupt vapours "que apagan las luces, extinguen, y aniquilan los espiritus de los hombres", reproduces in words the furnace ventilator it prints as figures 10 and 11 of its Plancha 3 — brick furnace, ash-pit, tile-or-iron duct through the firebox, wooden ducts sealed with glue and parchment, funnel mouth in the deep, chimney draught, replacement air down a second shaft — and records the reason the author gives for preferring it, that it "ahorra la fatiga de los Operarios, que se emplèan en manejar fuelles". It then shows the requirement becoming law in the 1783 royal ordinances, whose article on adits demands lumbreras or a contracañón "para mantener siempre en la obra la libre ventilacion y desaogo de los Operarios". Against all of which it sets, without softening, that the author claims none of the invention as his own, that Humboldt found the underlying physics still misunderstood in the mines sixty years later, and that not one page read here shows the machine built, an inspection made, or a single miner named.
Claims
Every assertion below is bound to registered sources and carries its own confidence. Weight them; do not treat the page as uniformly authoritative.
The problem is stated as a second obstacle equal to the water. "No solo las aguas impiden la labor de las Minas, sino los vapores corruptos de sus Cabernas, de que es preciso que huyan los Operarios, para no quedar sofocados dentro de ellas; pues al modo que apagan las luces, extinguen, y aniquilan los espiritus de los hombres con la pestilencial malignidad que exhala el Arsenico, y otros cuerpos minerales crassos, inflamables, y de materias sulfureas." The test named — that the bad air puts out the lamps before it kills the man — is the working sign miners used, and the aetiology offered, arsenical and sulphurous exhalations, is the chemistry of the period rather than a modern account of firedamp and blackdamp.
Before proposing anything the commentary surveys the European art, by name. To refresh these places with pure airs and extract the corrupt vapours, "se inventò en Inglaterra por el Doctor Hales una máquina Ventilatoria, que consiste en una rueda encerrada en una grande caxa, cubierta por lo alto, la qual se ha de mover rapidissimamente, y hace por consequencia mucho viento, que por precision desciende, no pudiendo escapar por arriba". "Monsieur Lohneis en su Descripcion del trabajo de las Minas" is credited with other means, especially square wooden pipes whose joints must be exactly fitted and covered, shaped like a chimney and fitted for the deepest places; and where they come out to the light at a shaft the sun must be kept from entering, "porque impediria la circulacion del ayre, y dexaria estancado el de los subterraneos" — this last referred to "el Arte de Minas de Juan Gotlob Lehmann, traducido del Alemàn al Francès", cited in the footnote as L'art des Mines, Paris 1759, chapitre 3, pages 49 and 50. These are the commentator's citations of works not opened here, and the confidence is set for that.
The device he recommends is described well enough to be built, and it is printed with figures. Of all the inventions for renewing the wind and drawing out the corrupt air, "ninguna es comparable à la máquina de fuego, que al margen del citado lugar trahe el Traductor de Monsieur Lehmann, con las dos Figuras, que copiamos en la Plancha 3", figure 10 giving the perspective of a furnace and the mouth of a shaft, figure 11 a section of furnace and mine "como si se viera en sus entrañas". Beside the shaft a brick furnace A is built, with its ash-pit at B and firebox at C; the duct D passes through the firebox and must be of tile or well-cast iron in the part nearest the fire, while the rest of it, DE and EF, laid underground, may be of wood, "cuyas junturas se deberàn cerrar con la mayor exactitud, y perfeccion con cola fuerte, y pedazos de pergamino". The ducts may be lengthened in proportion to the depth of the mine, given angles and turns to follow the interior ways, and the deep end F is to be made "en forma de embudo, ò trampa, para que recoja, y atrayga el ayre con mayor facilidad, y fortaleza".
The principle of operation is stated plainly. The machine set, the firebox is lit; once the fire has taken body its door is closed and so is the ash-pit's, "y entonces el calor atraherà fuertemente el ayre de los subterraneos, que entrando por la extremidad del Cañon F, saldrà por la Chimenèa del Horno G; y mientras mas elevada la Chimenèa, el fuego atraherà mas vivamente el ayre de los subterraneos. El ayre exterior, entrando por el Pozo H, reemplazarà el extrahido por el fuego." It is a furnace draught producing forced circulation between two openings, with the taller chimney giving the stronger pull.
The reason given for preferring it is the workmen's labour, not the owner's yield. "Esta máquina es muy facil, y poco costosa, y se experimentan en su práctica los mejores efectos de las Minas, pues ahorra la fatiga de los Operarios, que se emplèan en manejar fuelles, u otros instrumentos, para refrescar los subterraneos: y puede usarse de ella en todos tiempos de viento, ò calma, como se practìca en los lugares, en que se quiere renovar el ayre, extrayendo el corrupto, como Bodegas de Navìos, Salas de Hospitales, y en los Theatros, ò Espectáculos." The comparison set is worth keeping: ships' holds, hospital wards and theatres — the standard eighteenth-century catalogue of enclosed places whose air was understood to need changing.
The attribution is honest on the page and this entry keeps it that way. Gamboa does not claim the ventilator as his invention or as an American one: he names the English machine as Hales's, the pipes as Löhneyss's, and the furnace as the one the French translator of Lehmann gives in the margin of the passage, saying of the two figures only "que copiamos en la Plancha 3". What is his, and what is of interest here, is the act of carrying that European apparatus into a commentary on the mining law of New Spain and recommending it for the mines of that kingdom on the ground that it spares the operarios.
Twenty-two years later ventilation for the workmen appears as a command in the royal code. Article 7 of the título on adits of the Reales ordenanzas de minería of 1783 requires "que se han de labrar las correspondientes Lumbreras, ó llevarse un Contracañon, ó algun otro arbitrio suficiente para mantener siempre en la obra la libre ventilacion y desaogo de los Operarios"; and article 8, capping the adit's size, requires that it be driven within two varas of width and three of height, "llevándose siempre con seguridad, y bien ademado", its amplitude determined by the Facultativo according to circumstances. Air shafts, a parallel gallery or some sufficient equivalent are thus made a condition of the work, and the reason given in the article is the ease of the men working in it.
Ventilation was also expected from the ordinary structure of the workings. In the chapter on pillars Gamboa notes that these serve not only to hold the ground and to fix the ladders but also so "que el ayre devane, y aya respiracion en las labores" — the pillars dividing the excavation into passages through which air could move. A mine stripped of its pillars was therefore, on the same page, both a mine liable to collapse and a mine without air.
Sixty years afterwards Humboldt states the physics and corrects a belief current in the mines. Writing of the workings of Valenciana, where exploratory galleries eight or nine metres high had been driven, he says: "Es un error el imaginar que esta grande altura facilite la renovacion del aire; la ventilacion depende únicamente del equilíbrio y de la diferencia de temperatura de dos columnas de aire que estén próximas." That is exactly the principle the furnace ventilator exploits, since heating one column is what sets the circulation going; reading the two passages together as cause and description is this entry's inference and not a connection either author makes, and the confidence is set accordingly.
The limits are severe and belong on the record. No page read here shows a furnace ventilator ever built in a mine of New Spain: the machine is a recommendation in a law book, illustrated by figures copied from a French translation of a German work. No page read gives a count of men killed or disabled by bad air, a case, a compensation, an inspection made under the 1783 article, or one sentence from any operario. Humboldt, who went underground at Valenciana and Real del Monte and wrote at length on their air, describes no furnace ventilator in use. And the protection the ordinance offers is stated as a condition of driving an adit, in a code whose subject is the yield of mines; nothing here licenses the conclusion that the mines of New Spain were healthy places to work.