1. De salibus alkalino-fixis et camphora.
2. De succino, opio, caryophyllis aromaticis et castoreo.
3. On saltpetre, sulphur, antimony, and iron.
4. On tea, coffee, beer, and wine.
5. Disquisitio de ambragrysea.
6. On common salt, tartar, sal ammoniac and ants.
After Neumann’s death, two copies of his chemical lectures were published. The first consisting of notes taken by one of his pupils, intermixed with incoherent compilations from other authors, was printed at Berlin in 1740. The other was printed by the booksellers of the Orphan Hospital of Zullichau (the place of Neumann’s birth), and is said to have been taken from the original papers in the author’s handwriting. Of this last an excellent translation, with many additions and corrections, was published by Dr. Lewis, in London, in the year 1759; it was entitled, “The Chemical Works of Caspar Neumann, M.D., Professor of Chemistry at Berlin, F.R.S., &c. Abridged and methodized; with large additions, containing the later discoveries and improvements made in Chemistry, and the arts depending thereon. By William Lewis, M.B., F.R.S. London, 1759.” This is an excellent book, and contains many things that still retain their value, notwithstanding the improvements which have been made since in every department of chemistry.
I have reason to believe that the laborious part of this translation and compilation was made by Mr. Chicholm, whom Dr. Lewis employed as his assistant. Mr. Chicholm, when a young man, went to London from Aberdeen, where he had studied at the university, and acquired a competent knowledge of Greek and Latin, but no means of supporting himself. On his arrival in London, one of the first things that struck his attention was a Greek book, placed open against the pane of a bookseller’s window. Chicholm went up to the window, at which he continued standing till he had perused the whole Greek page thus exposed to his view. Dr. Lewis happened to be in the shop: he had been looking out for a young man whom he could employ to take charge of his laboratory, and manage his processes, and who should possess sufficient intelligence to read chemical works for him, and collect out of each whatever deserved to be known, either from its novelty or ingenuity. The appearance and manners of Chicholm struck him, and made him think of him as a man likely to answer the purposes which he had in view. He called him into the shop, and after some conversation with him, took him home, and kept him all his life as his assistant and operator. Chicholm was a laborious and painstaking man, and by continually working in Lewis’s laboratory, soon acquired a competent knowledge of chemistry. He compiled several manuscript volumes, partly consisting of his own experiments, and partly of collections from other authors. At Dr. Lewis’s death, all his books were sold by auction, and these manuscript volumes among the rest. They were purchased by Mr. Wedgewood, senior, who at the same time took Mr. Chicholm into his service, and gave him the charge of his own laboratory. It was Mr. Chicholm that was the constructor of the well-known piece of apparatus known by the name of Wedgewood’s pyrometer. After his death the instrument continued still to be constructed for some time; but so many complaints were made of the unequal contraction of the pieces, that Mr. Wedgewood, junior, who had succeeded to the pottery in consequence of the death of his father, put an end to the manufacture of them altogether.
John Henry Pott was born at Halberstadt, in the year 1692. He was a scholar of Hoffmann and Stahl, and from this last he seems to have imbibed his taste for chemistry. He settled at Berlin, where he became assessor of the Royal College of Medicine and Surgery, inspector of medicines, superintendent of the Royal Laboratory, and dean of the Academy of Sciences of Berlin. He was chosen professor of theoretical chemistry at Berlin; and on the death of Neumann, in 1737, he succeeded him as professor of practical chemistry. He was beyond question the most learned and laborious chemist of his day. His erudition, indeed, was very great; and his historical introductions to his dissertation displays the extent of his reading on every subject of which he had occasion to treat. It has often struck me that the historical introductions which Bergmann has prefixed to his papers, are several of them borrowed from Pott. The Lithogeognosia of Pott is one of the most extraordinary productions of the age in which he lived. It was the result of a request of the King of Prussia, to discover the ingredients of which Saxon porcelain was made. Mr. Pott, not being able to procure any satisfactory information relative to the nature of the substances employed at Dresden, resolved to undertake a chemical examination of all the substances that were likely to be employed in such a manufacture. He tried the effect of fire upon all the stones, earths, and minerals, that he could procure, both separately and mixed together in various proportions. He made at least thirty thousand experiments in six years, and laid the foundation for a chemical knowledge of these bodies.[181] It is to this work of Pott that we are indebted for our knowledge of the effects of heat upon various earthy bodies, and upon mixtures of them. Thus he found that pure white clay, or mixtures of pure clay and quartz-sand, would not fuse at any temperature which he could produce; but clay, mixed with lime or with oxide of iron, enters speedily into fusion. Clay also fuses with its own weight of borax; it forms a compact mass with half its weight, and does not concrete into a hard body when mixed with a third of its weight of that salt. Clay fuses easily with fluor spar; it fuses, also, with twice its weight of protoxide of lead, and with its own weight of sulphate of lime, but with no other proportion tried. It was a knowledge of these mutual actions of bodies on each other, when exposed to heat, that gradually led to the methods of examining minerals by the blowpipe. These methods were brought to the present state of perfection by Assessor Gahn, of Fahlun, the result of whose labours has been published by Berzelius, in his treatise on the blowpipe. Pott died in 1777, in the eighty-fifth year of his age.
His different chemical works (his Lithogeognosia excepted) were collected and translated into French by M. Demachy, in the year 1759, and published in four small octavo volumes. The chemical papers contained in these volumes are thirty-two in number. Some of these papers cannot but appear somewhat extraordinary to a modern chemist: for example, M. Duhamel had published in the memoirs of the French Academy, in the year 1737, a set of experiments on common salt, from which he deduced that its basis was a fixed alkali, which possessed properties different from those of potash, and which of course required to be distinguished by a peculiar name. It is sufficiently known that the term soda was afterwards applied to this alkali; by which name it is known at present. Pott, in a very elaborate and long dissertation on the base of common salt, endeavours to refute these opinions of Duhamel. The subject was afterwards taken up by Margraaf, who demonstrated, by decisive experiments, that the base of common salt is soda; and that soda differs essentially in its properties from potash.