IN

LETTER IV.

The method of making Saltpetre in Spain.

the year 1754, I received orders * from the miniftry to inspect into feveral faltpetre works, as well as into the making of gunpowder, which having complied with, the following reflections. occurred to my mind.

All the profeffors of chemistry I had converfed with, either in France or in Germany, laid down as a fixed principle, that there are three mineral acids in nature that the vitriolic, is the universal one, belonging to metals, from whence the other two arife. That the nitrous is fecond in activity, and belongs to the vegetable kingdom, and the marine being the weakest of all, is homogeneous to fish. They do not include the animal acid, which united with the phlogifton, § forms the phosphorus. I was further taught, that the fixed alkali

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*Don Guillermo Bowles.

By phlogifton, chemists mean the most pure and fimple inflammable principle, concerning which there are a great variety of opinions and doctrines, fupported on the one hand, and controverted on the other with equal ingenuity, by chemical writers.

alkali of faltpetre, did not exist purely, and fimply in nature, but was generated by fire, and when they found faltpetre, to be dug out of the earth naturally in the Eaft Indies, they thought to fave the difficulty, by faying it proceeded from the incineration of woods, which had impregnated the earth, with this fixed alkali, the basis of faltpetre; fo that I had been led to believe, it was formed by certain combinations, that took place in the act of combustion; but I foon found my error, when I had feen the method of making faltpetre in the different provinces of Spain. I have now evident proofs that the basis of nitre really exifts in the earth and in plants, the fame as in the Soda of Alicant. Let thefe learned gentlemen come to Spain, they may convince themfelves of this truth, and fee faltpetre with its alkaline bafis, in the manufactures of Caftile, Aragon, Navarre, Valencia, Murcia, and Andalufia, where it is made without the affiftance of vegetable matter; fometimes throwing in a handful of ashes of matweed, merely to filter the lye of earth, and though they often meet with gypseous ftone in the neighbourhood of their works, yet they make excellent faltpetre by boiling the lixivium of their lands only, in which they do not find an atom of gypfum; confequently they have gunpowder in Spain, without being indebted for its fixed alkali, to the vegetable kingdom,

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and without the vifible or fenfible conversion of the vitriolic acid of gypfum into the nitrous.

Having thus difcovered in Spain a perfect fixed alkali in the earth, I pursued my observations on other falts, and vegetable productions, and after many reflections and experiments, I discovered that fimilar fixed alkalies, many oils, and neutral falts, proceed from different combinations of the air, earth, and water, with fuch matters as the air conveys in a diffolved ftate, and that these three elements, rifing, falling, and meeting, combine together, and form new bodies in the organs of vegetation,

Those who are verfed in phyfics, agree, that all the fubftances of the very globe we inhabit, confift of the combinations of fire, water, earth, and air; why then deny them the power of combining, in the living organs of plants? when we so often perceive in them, the faculty of changing, and transforming productions in the kingdom of nature. In proof of it, we find that many cruciformed plants give by analysis, the fame volatile alkali as animals, notwithstanding that their tubes are fimilar to the eye, with thofe that give acids.

Some plants have their roots fo fmall, and yet their branches, leaves and fruit fo ponderous, that it appears impoffible, fo inconfiderable a root

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fhould

should draw fufficient nurture out of the earth for fuch various purposes. It feems therefore, that the ambient air, containing many diffolved bodies, penetrates into the plants, and combines in the vegetative tubes, forming those fubftances difcovered by analysation.

I have frequently feen water melons in Spain weigh from twenty to thirty pounds, with a ftem of only two or three ounces, fo great was the increase of the fibrous and tubulous fubftance of thofe plants, owing to the watery particles they imbibed from the air. It fhould feem then, that many plants draw their principal fupport from the air, water, and a small portion of earth, combined by the imperceptible labour of the vegetative tubes, and veffels of air, which convert those matters into the products we contemplate, and tafte;. many plants producing all these effects in water only, and we find that mint, and other odoriferous plants whose roots grow in water, and in the air, give the fame fpiritus rector, and oils, as thofe that grow in the earth.

Botanifis know very well that those aquatic plants that fpring up from the bottom of waters have a very trifling deviation, the fame properties and qualities in the frozen regions, as in fultry and parching climates, and, that their acrimony, cauflicity, infipidity, and coolness, are invariable.

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The experiments made by Van Helmont on the willow tree, making it grow in water, and a small portion of dried earth, fhew how much air, and water, added to the internal labour of plants, contribute to vegetation.

In the memoirs of the French academy of sciences, we find experiments of a celebrated chemist, to prove the existence of three neutral falts in the extract of borrage. If he had gone further, and proved that one of these three falts, exifted in the earth, which produced the borrage, he would have illuftrated the fyftem of physics, and cleared up the point I am speaking of. The same memoirs mention another academician, who reared an oak for many years, only with water, the confequences of which speak for theinfelves.

There are millions of firs about Valladolid, and Tortofa, replete with turpentine, and growing in a fmall portion of earth, and great quantity of fand, in which it would be difficult to prove that the thousandth part of the turpentine, so plentifully produced by these trees, had exifted; of course, it must be owing to channels of air, connected with the tubes of vegetation.

The conductory veffels of the wormwood of Granada, convey a bitterness to the very juice of the fugar cane, which grows by its fide; the foil of

the