that assertion founded, which we read in English and French authors, that the preparation of ultramarine was found out in England, and that a servant of the East India Company disclosed it, in order to be revenged for some injury which he had sustained?

[The following is the method of making ultramarine from lapis lazuli. The finest mineral is selected, heated to a dull red heat, and quenched in water; it is thus rendered friable, and is ground down into an impalpable powder. This is then mixed with a tenacious paste made of linseed oil, wax, resin, turpentine and mastic; and the mixture being kneaded in Gobet, in Les Anciens Minéralogistes de France, Paris, 1779, 8vo, ii. p. 705, tells us that this Jerome Ruscellai died in 1565; and that his book was composed from his papers by Franc. Sansovino, who published many works not his own, and printed for the first time at Milan, in 1557. I have nowhere found a particular account of this Ruscellai; and indeed it is always laborious to search out any of that noble family, which I have already spoken in the article Lacmus. He appears to me to be none of those mentioned in Jochers Gelehrten-Lexicon. I have met with no earlier edition of his works than that of 1557: but I suspect that the first must be older. However much the book may have been sought after, it seems to me improbable that three editions should be published in Italian in the course of the first year; for, besides that of Milan, two editions printed at Venice the same year, one in quarto and another in octavo, are still extant. A French translation also was published at Antwerp, in 1557. Is it possible that an English translation could be published at London in 1558, if the original appeared for the first time only in 1557? At that period translations were not made so speedily. The Secrets of Alexis, London, 1558, is mentioned in Ames's Typographical Antiquities, p. 296. I have in my possession a French translation by Christofle Landré, Paris, 1576, 12mo, which I seldom find quoted. It has a large appendix, collected from various authors.

It is well-known that Joh. Jacob Wecker, a physician at Colmar, translated into Latin this book of Alexius, and enlarged it with additions, under the title of De Secretis Libri xvii. The first edition, as Haller says, was printed at Basle in 1559, 8vo. Every edition seems to differ from the preceding; many things are omitted, and the new additions are for the most part of little importance. I have the edition of Basle, 1592, 8vo, in which there is a great deal not to be found in that of 1662, and which wants some things contained in the edition of 1582. The latest editions are printed from that improved by Theod. Zwinger, Basle, 1701, 8vo. The last by Zwinger, was published at Basle in 1753. Though these books on the arts, as they are called, contain many falsehoods, they are still worthy of some notice, as they may be reckoned among the first works printed on technology, and have as much induced learned men to pay attention to mechanics and the arts, as they have artists to pay attention to books and written information. 1 See Savary, Dict. de Commerce, art. Outremer, which has been copied into Rolt's Dictionary of Trade, Lond. 1756, fol.

warm water gives out the blue particles, which are afterwards collected by subsidence.

Chemists are not agreed concerning the cause of the colour of ultramarine. Dr. Elsner considers it to arise from sulphuret of sodium and of iron, the former being a higher sulphuret than the latter. MM. Clement and Desormes show that the iron is not essential, either to the lapis lazuli, or to the pigment made from it.

An artificial method of making ultramarine was discovered in 1828 by M. Guimet; the process has been kept secret. Processes have also been discovered by M. Gmelin of Tübingen, M. Persoz of Strasburg, and others. M. Gmelin's process consists in fusing a mixture of two parts of sulphur and one of dry carbonate of soda in a Hessian crucible, and then sprinkling into it by degrees another mixture of silicate of soda and aluminate of soda. The crucible must be exposed

to the fire for an hour after this. The ultramarine thus prepared contains a little sulphur, which can be separated by means of water.

Some valuable observations on this subject have lately been published by M. Prückner 1. He states that the materials required in the preparation of ultramarine are alumina, sulphate of soda, sulphur, charcoal and a salt of iron, the common sulphate or green vitriol being the best. The alumina is supplied in white bole, or a very pure white clay. The sulphate of soda is reduced by charcoal and heat to the state of sulphuret, and its solution thus obtained afterwards boiled with sulphur so as to form a persulphuret (penta-sulphuret, Berz.). The solution is then mixed with the dried clay and stirred; during the mixing a solution of green vitriol is added and mixed. It is then dried and very finely powdered as rapidly as possible. It is afterwards heated in a muffle; then washed, drained and again heated in a muffle; finally it is again washed, dried and powdered.]

1 Chemical Gazette, May 31, 1845.

COBALT, ZAFFER, SMALT.

THE name cobalt is given at present to that metal and its ores, the oxides of which are largely employed in the manufactures of glass, porcelain and pottery, for the production of a blue colour. The cobalt ores are first roasted and freed from foreign mineral bodies, particularly sulphur, iron, nickel, bismuth, and arsenic, with which they are united, and then well calcined, and sold, either mixed or unmixed with fine sand, under the name of zaffer (zaffera); or the cobalt is melted with siliceous earth and potash to a kind of blue glass called smalt, which, when ground very fine, is known in commerce by the name of powder-blue. All these articles, because they are most durable pigments, and those which best withstand fire, and because one can produce with them every shade of blue, are employed, above all, for tinging crystal and for enamelling; for counterfeiting opake and transparent precious stones, and for painting and varnishing real porcelain and earthen and potters' ware. This colour is indispensably necessary to the painter when he is desirous of imitating the fine azure colour of many butterflies and other natural objects; and the cheaper kind is employed to give a blueish tinge to new-washed linen, which so readily changes to a disagreeable yellow.

The preparation of this new colour may be reckoned among the most beneficial inventions of modern times. It rendered of importance an useless and hurtful production; gave employment to a number of hands; assisted in bringing many arts to a degree of perfection which they could never before attain; and has drawn back to Germany a great deal of money which was formerly sent out of it for foreign articles.

Though there is no doubt that the process used in the preparation of cobalt and smalt was invented about the end of the fifteenth or the beginning of the sixteenth century, we have reason to ask whether the ancients were acquainted with cobalt, and if they employed it for colouring glass. They opened and worked mines in various parts; and it is at any rate possible that they may have found cobalt; they made many successful attempts to give different tints to glass'; and they

1 See what is said under the article Artificial Rubies.

produced blue glass and blue enamel. They may have learned by an accident to make this glass, as they did to make brass; and they may have continued to make the former as long as their supply of coloured earth lasted. When the mineral failed them, they may have lost the art, in the same manner as the method of preparing Corinthian brass was lost for a considerable space of time. The use of cobalt does not imply a knowledge of its metal; for the moderns made brass and smalt for whole centuries, before they learned to prepare zinc and regulus of cobalt.

It seems, however, difficult to answer this question; for one can scarcely hope to discover cobalt with any certainty among those minerals mentioned by the ancients. They could describe minerals in no other manner than according to their exterior appearance, the country where they were found, or the use to which they applied them. Now there is no species more various and more changeable in its figure and colour than cobalt ore, which on this account shows the impossibility of distinguishing minerals with sufficient accuracy by external characteristics. Besides, there are scarcely two passages of the ancients which seem to allude to it; and these, when closely examined, give us little or no information.

The meaning of the term cadmia is as various and uncertain as that of the word cobalt was two centuries ago. It signified often calamine; sometimes furnace-dross; and perhaps, in later times, also arsenic; but, as far as I know, it was never applied to cobalt till mineralogists wished in modern times to find a Latin term for it, and assumed that which did not belong properly to any other mineral. The well-known passage of Pliny 3, in which Lehmann thinks he can with certainty distinguish cobalt, is so singular a medley that nothing to be depended on can be gathered from it. The author, it is true, where he treats of mineral pigments, seems to speak of a blue sand which produced different shades of blue paint, according as it was pounded coarser or finer. The palest powder was called lomentum; and this Lehmann considers as our powderblue. I am however fully convinced that the cyanus of Theophrastus, the cœruleum of Pliny, and the chrysocolla +, were 1 See the Annotatious on Arist. Auscult. Mirab. p. 98.

2 I am of opinion that this Latin name for cobalt was first used by Agri3 Lib. xxxiii. cap. 13. Theophrast. De Lapid. 97.

4 Aristot. Auscult. Mirab. p. 123.

the blue copper earth often already mentioned, which may have been mixed and blended together. Besides, Pliny clearly adds to it an artificial colour, which in my opinion was made in the same manner as our lake; for he speaks of an earth, which when boiled with plants, acquired their blue colour, and which was in some measure inflammable. With these pigments walls were painted; but as many of them would not endure lime, they could be used only on those which were plastered with clay (creta). The expression usus ad fenestras has been misapplied by Lehmann, as a strong proof of his assertion; for he explains it as if Pliny had said that a blue pigment was used for painting window-frames; but glass windows were at that time unknown. I suspect Pliny meant to say only that one kind of paint could not be employed near openings which afforded a passage to the light, as it soon decayed and lost its colour. This would have been the case in particular with lake in which there was a mixture of vegetable particles.

For my part, I find in this passage as few traces of smalt as M. Gmelin; and I agree with him in opinion that the strong and unpleasant mixtures arising from cobalt would, had it been known, have induced the ancients to make particular mention of it in their writings. Would not the arsenic, which is so often combined with cobalt, have given occasion to many reports respecting the dangerous properties of these minerals? And would not arsenic and bismuth have been sooner known, had preparations of cobalt been made at so early a period? It is a circumstance of great weight also, that in the places where the ancients had mines, and where antiquities painted or tinged blue, and resembling in colour that produced by cobalt, have been dug up, cobalt has not been discovered, or has been discovered only in modern times. At present we know nothing of Egyptian, Arabian, Ethiopian, Italian, and Cyprian cobalt; and in Spain1 this mineral was first found in the reign of Philip IV. I shall here observe, that the island of Cyprus was formerly so abundant in copper, that, in a mineralogical sense, it might be called the island of Venus; and we can therefore entertain the less doubt that the cæruleum Cyprium was copper-blue.

1 Bowles, Introducion à la Historia Natural y à la Geographia Fisica de España.-Madrit, 1775 p. 399.