arts, and requested him to try it. He drew a tree with oil varnish and colours on a plate of glass, applied the acid to the plate in the usual manner, and then removed the varnish. By these means a bright, smooth figure was produced upon a dim ground, which had a much better effect than those figures that are cut into the glass. I recommend this process, because I am of opinion that it may be brought to much greater perfection; and M. Renard, that celebrated artist of Strasburg, whose thermometers with glass scales, in which the degrees and numbers are etched, have met with universal approbation, was of the same opinion, when I mentioned the method to him while he resided here, banished from his home by the disturbances in his native country

It is probable that Schwanhard and his scholars kept the preparation of this liquid a secret, as the receipt for that purpose was not made known till the year 1725, though it is possible that one older may be found in some of those books which treat on the arts. In the above-mentioned year, Dr. John George Weygand, from Goldingen in Courland, sent to the editor of a periodical work a receipt which had been written out for him by Dr. Matth. Pauli of Dresden, then deceased, who had etched, in this manner on glass, arms, landscapes, and figures of various kinds1. We find by it that a strong acid of nitre was used, which certainly disengages the acid of fluor-spar, though the vitriolic acid is commonly employed for that purpose. That the Bohemian emerald or

1 Breslauer Sammlung zur Natur- und Medicin-Geschichte. 1725, January, p. 107. "Invention of a powerful acid by which figures of every kind, according to fancy, can be etched upon glass.-When spiritus nitri per distillationem has passed into the recipient, ply it with a strong fire, and when well dephlegmated, pour it, as it corrodes ordinary glass, into a Waldenburg flask; then throwinto it a pulverised green Bohemian emerald, otherwise called hesphorus (which, when reduced to powder and heated, emits in the dark a green light), and place it in warm sand for twentyfour hours. Take a piece of glass well cleaned and freed from all grease by means of a lye; put a border of wax round it, about an inch in height, and cover it all equally over with the above acid. The longer you let it stand the better, and at the end of some time the glass will be corroded, and the figures, which have been traced out with sulphur and varnish, will appear as if raised above the plane of the glass." This receipt has been inserted by H. Krunitz in his Ekonomische Encyclopedie, xi. p. 678. 2 Klindworth covers the glass with the etching ground of the engravers ; but in the Annals of Chemistry for 1790, ii. p. 141, a solution of isinglass

hesphorus, mentioned in the receipt, is green fluor-spar, cannot be doubted, and will appear still more certain from the history of this species of stone, as far as I am acquainted with it, which I shall here insert.

In the works of the old mineralogists, fluor-spar is either not mentioned, or is classed among their natural glasses and precious stones; and in those of the first systematic writers it is so mingled with quartz and calcareous and gypseous spars, that it is impossible to discover it. The old German miners, however, distinguished it so early as the sixteenth century, and called it fluss; because they used it to accelerate the fusion of ores that were difficult to be reduced to that state. Agricola, who first remarked this, changed the German name into fluor, an appellation, which, like many others, formed by him from German words, such for example as quarzum from quarz, spatum from spat, wismuthum, zincum, cobaltum, &c., became afterwards common. If a passage of the ancients can be quoted that seems to allude to fluorspar, it is that of Theophrastus, where he says that there are certain stones which, when added to silver, copper, and iron ores, become fluid'. The first systematic writer who mentioned this kind of stone as a particular genus, was Cronstedt.

Besides being known by its metallurgic use, fluor-spar is known also by having the colours of some precious stones, so that it may be sold, or at least shown as such to those who are not expert judges; because the first time when heated in the dark it shines with a bluish-green lustre. It is possible that fluor-spar may have been among the number of that great variety of stones which the ancients, with much astonishment, tell us shone in the dark; though it is certain that the principal part of them were only light-magnets, as they are called, or such as retain for a certain period the light they have absorbed in the day-time. The observation, however, that fluor-spar emits light after it is heated, seems to have been first made when artificial phosphorus excited the inquiry of naturalists and chemists; and when they began to search in their own country for stones which, in the property of emitin water, or a turpentine oil varnish, mixed with a little white lead, is recommended. Complete instructions for acquiring this art may be found there also. 1 De Lapidibus, sect. 19.

ting light, might have a resemblance to the Bologna spar, made known about the year 1630. It is well known that the latter is prepared for that purpose by calcination. Stones of the like kind were sought for; and among these fluor-spar, which is not scarce in Germany.

In my opinion, the observation was made in the year 1676; for in that year Elsholz informed the members of the Society for investigating Nature, that he was acquainted with a phosphorus which had its light neither from the sun nor from fire, but which, when heated on a metal plate over glowing coals, shone with a bluish-white lustre; so that by strewing the powder of it over paper, one might form luminous writing. I doubt much whether this experiment was ever tried; at least I find no further account of it in the papers of the Society, nor in the re-publication of the above author's first dissertation, which appeared in 1681 1.

As far as I know, Kirchmaier, professor at Wittenberg, was the first who disclosed the secret, in the year 16792. Both call this phosphorus the smaragdine; because the ancients speak much of luminous emeralds, and because green fluorspar is often exhibited as an emerald. Kirchmaier calls this mineral also hesperus and vesperugo; and these names have been often given since to fluor-spar, as in the receipt before mentioned for making a liquid to etch on glass. Kirchmaier's information, however, must have been very little known; for the Jesuit Casatus, who, in 1684, wrote his Treatise on Fire, was not acquainted with it, as he has inserted only the words of Elsholz. This observation must have been new to Leibnitz himself, and to the Academy of Sciences at Berlin, in 1710; for the former then mentioned it to the Society as a philosophical novelty".

I shall remark, in the last place, that the manufacturing of vessels and ornaments of every kind from solid fluor-spar was

1 See Ephemerid. ac Nat. Cur. 1676, Dec. 1, obs. 13, p. 32; and Elsholtii De Phosphoris Observationes, Berol. 1681, 4to.

G. C. Kirchmaieri De Phosphoris et Natura Lucis, necnon de Igne, Commentatio Epistolica. Wittebergæ, 1680, 4to.

3 Miscellanea Berolin. 1710, vol. i. p. 97. The fluor-spar earth, or phosphoric earth, as it is called, which in later times has been found in marble quarries, and which some at present consider as an earth saturated with phosphoric acid, is mentioned by the Swede Hierne, in Prodromus Hist. Nat. Sueciæ. Henkel had never seen it.

begun in Derbyshire in the year 17651. The articles formed of it are in England called spar ornaments, and sometimes blue John. Many beautiful colours must, as is said, be brought forward by means of fire. But the heat must be applied with great caution; for fluor-spar, as is well known, by a strong and particularly a sudden heating, cracks, and loses its transparency. Since writing the above, I find that M. Raspe2 denies this bringing forward of colours by fire.

SOAP.

THAT the first express mention of soap occurs in Pliny and Galen, and that the former declares it to be an invention of the Gauls, though he prefers the German to the Gallic soap3, has already been remarked by many. Pliny says that soap was made of tallow and ashes; that the best was made of goats' tallow and the ashes of the beech-tree, and that there were two kinds of it, hard and soft. The author of a work on simple medicines, which is ascribed to Galen, but which however does not seem to have been written by that author, and of which only a Latin translation has been printed, speaks of soap being made by a mixture of oxen, goats', or sheep's tallow, and a lye of ashes strengthened with quicklime. He says the German soap was the purest, the fattest, and the best, and that the next in quality was the Gallic'. This account corresponds more exactly with the process used in Germany at present; whereas the French use mineral alkali, and instead of tallow, employ oil, which appears to be a later in

1 Watson's Chemical Essays, ii. p. 277. 2 Descriptive Catalogue of Tassie's Engraved Gems, Lond. 1791, 2 vols. 4to, i. p. 51. 3 Plin. xviii. 12, sect. 51, p. 475.

4 It is beyond all doubt that the words sapo and σáπwv were derived from the German sepe, which has been retained in the Low German, the oldest and original dialect of our language. In the High German this derivation has been rendered a little more undistinguishable by the p being changed into the harder f. Such changes are common, as schap, schaf; schip, schiff, &c. 5 De Simplicibus Medicaminibus, p. 90, G.

vention. Pliny in his description does not speak of quicklime; but as he mentions a mixture of goats' tallow and quicklime a little before, it is probable that the use of the latter was then known at Rome. Gallic and German soap are often mentioned by later writers', as well as by the Arabians, sometimes on account of their external use as a medicine, and sometimes on account of their use in washing clothes. The latter purpose is that for which soap is principally employed in modern times; but it does not seem to have been the cause of German soap being introduced at Rome. Washing there was the occupation of indigent scourers, who did not give themselves much trouble concerning foreign commodities. The German soap, with which, as Pliny tells us, the Germans coloured their hair red, was imported to Rome for the use of the fashionable Roman ladies and their gallants. There is no doubt that the pila Mattiace, which Martial recommends as a preventive of gray hair2; the caustica spuma with which the Germans dyed their hair3; and the Batavian froth or lather which the Romans employed for colouring theirs, were German soap. It is probable that the Germans tinged it with

1 According to Aretaus De Diuturnis Morbis, ii. 13, p. 98, soap appears to have been formed into balls.

2 Mart. xiv. 27. This soap acquired the epithet of Mattiacum from the name of a place which was in Hesse.

3 Caustica Teutonicos accendit spuma capillos,

Captivis poteris cultior esse comis.-Mart. xiv. 26.

These lines are generally explained in this manner:-" Dye thy hair with soap, and it will become more beautiful than that of the Germans." But in this case all the wit of the advice is lost; and the expression, "eris cultior quam comæ captivæ," seems to me to be very improper. I should rather translate them as follows:-"Let the Germans dye their hair with pomade; as they are now subdued, thou mayst ornament thyself better with a peruke made of the hair of these captives." This was a piece of delicate flattery to Domitian and the Roman pride. That prince thought he had conquered the Germans; and the most beautiful German hair, that which was not dyed, could be procured, therefore, at Rome, much easier than before. If the title of this epigram was written by Martial himself, it contains the first mention of the word sapo.

4 Fortior et tortos servat vesica capillos,

Et mutat Latias spuma Batava comas.-Mart. viii. 23, 19.

The first line of the above proves that people then covered their heads, in the night time, with a bladder to keep their hair, after it was dressed, from being deranged; and a bladder was undoubtedly as fit for that use as the nets and cauls employed for the like purpose at present.