Scheelite.

When searching for minerals at the head of Lake Wakatipu, in November, 1880, in company with Mr. Pryde, of Bannockburn, we learned that a heavy white substance occurred a short distance up the Bucklerburn Creek, not more than a mile from the north shore of the Lake. Finding the outcrop of what appeared to be a large quartz reef, we put a cut into it, and with little trouble exposed a lode of scheelite 3ft. 6in. in width. As the outcrop of the lode was easily traced, we marked out a claim about one mile in length, embracing all the ground easily got at and containing the outcrop. There is not a doubt as to the extent and permanency of the lode, and as the Lake steamboats can get to within a mile of it, the ore can be put on board at a trifling cost per ton. We had 15 bags of the ore taken out and forwarded, some to England and page 4 some to Scotland, to be tested. From England we have an offer from one firm of £8 to £10 per ton for the ore in its natural state, from another firm an offer to erect the necessary works to extract the various substances found in the ore. As yet we have no returns from Scotland, but these offers will be sufficient to show that the consignment sent to London fell into the hands of those who knew something about it. The ore has been repeatedly analyzed. On October, 6, 1881, it was analysed by Robert H. Davies, F.H.F.C., Chemist to Apothecaries' Hall, Public Analyst for the District of Fulham and Hamersmith, E.C., and was found to contain aluminum, potash, and tungstic acid, associated with quartz. The quantity of quartz varies according to whether the sample is a picked piece or taken promiscuously from the lode. As near as can be ascertained about one-third of the lode in bulk consists of scheelite. The question of separation of the quartz from the scheelite is only a matter of grinding and running the stuff over shaking tables, in order to separate the two by specific gravity—a very easy matter as the scheelite is more than six times the weight of quartz. This operation will cost about 10s. per ton of scheelite. I will therefore deal with the product of the lode as clean scheelite.

Tungstic acid was first discovered by Scheele, a celebrated German chemist, in 1781, just 100 years ago, and the mineral has been named after him, and is now known as Scheelite. For many years, indeed until well into this century, the metal was recognised only as a scientific curiosity. But amongst the many facts of applied science is the applica-tion of this rare metal to useful purposes. One prominent feature of this metal is it great weight, its specific gravity being 17.4, that of iron being 7.8. It will be seen to be two and a half times the weight of iron. It is found, in nature, as scheelite, and as an associate of sulphur, iron, and manganese. Not unfrequently the latter combination, known as wolfram, occurs in the tin mines of Cornwall, and for many years it baffled the skill of metallurgists to separate it from the tin ore, except at great cost. Now the difficulty has been overcome by adding soda to the pulverized tin ore, and calcining, when a tungstate of soda is formed, and the tin is relieved of a troublesome neighbour. On account of its frequent occurrence in tin, it came to be looked upon as a plentiful substance, but, when its value as an acid and an alloy was discovered and quantity was wanted, it was found to be very scarce. It may be said to be plentiful in the same sense as gold is plentiful in the auriferous drifts of Otago, but very hard to get in quantity.

Ure's Dictionary of Mines and Manufactures, page 924, says—"Amongst miners tungsten has the reputation of being an abundant mineral, but on close enquiry it is found to be comparatively rare, schoral, specular, and other iron ores and gossan being commonly mistaken for it."

The useful application of tungsten to manufactures is a fulfilment of the prediction of a great many chemists, but being of recent date its history is not yet written; but I am convinced, after twelve months' careful investigation, that tungstic acid and the metal tungsten will take a prominent place amongst the useful metals, will be much sought after, and, on account of the scarcity of scheelite, will become of still greater value.

page 5

Having perused all or nearly all the publications in which tungsten is referred to, I will quote from the most reliable authorities only.

Millen's Chemistry, part second, page 646 :—"Larient says—There are no fewer than six modifications of tungstic acid, each of which forms a distinct class of salts. This was disputed at the time, but it is now an established fact, and it is in this great range of division that its usefulness in the arts is apparent."

The metal has not been entirely unknown to the New Zealand chemists, scheelite having been found in water-worn boulders in the Bucklerburn as far back as 1864. It attracted the attention of the goldseeker on account of its great weight, and is known to the digger as "White Maori." A piece of ore from the creek at the head of Lake Wakatipu was exhibited at the New Zealand Exhibition held in Dunedin, 1865. Mr. Skey, who officiated as Analytical Chemist to the Exhibition, examined the scheelite, treated it in a variety of ways, and reported on it at great length : see Juror's Report, pages 414, 415, and 416. He formed a very high opinion of its value and usefulness, as will be seen from the following quotations :—"A very fine specimen of scheelite mixed with quartz, having the external appearance of quartz boulders, was exhibited by the Queenstown District Committee. From the specific gravity of this mineral there would be about 59.35 per cent, of pure tungstate of lime in the specimen." He goes on to say—"The metal tungsten and its compounds are attracting a good deal of attention at the present time (1865). It is thought by some that steel alloyed with a small quanity of this metal is much superior to any other kind of steel. Some of its soluble salts are used as mordants in the place of compounds of tin. Tungstate of lime and tungstate of lead are used as substitutes for white lead and oxide of zinc in painting. The salt called tungstate of soda, besides being used for a mordant, is employed to render fabrics non-inflammable. The clothes are steeped in a solution containing 20 per cent, of this salt, and then dried, when, unlike other salts recommended for this purpose, it does not interfere with the process of ironing, but allows the iron to go over the fabric smoothly. It is said to be used constantly in Her Majesty's laundry. The various oxides of tungsten afford excellent pigments of different colours. From a few hasty experiments made in the Laboratory certain new properties were observed sufficiently interesting and relative to this article to allow of their announcement here. The blue oxide was found to be soluble in certain acids, and the ben oxide in muriatic acid, under certain conditions, communicating respectively magnificent colours of blue, pink, or red. A brilliant ruby red pigment, in the form of crystals, was obtained by fusing tungstate of soda with the acetate for some time, and supposed to be benoxide of tungsten, but, from the pressure of other work, this substance has not yet been fairly studied. Recently it has also been discovered that the metal tungsten can be substituted for tin in the substance called 'Purple of Cassius' without affecting its properties for all the purposes to which it has been hitherto been applied, as far at least as can be determined. Indeed, this new Purple of Cassius is not to be distinguished from the genuine by its outward appearances.

"It will be seen, too, that inversely, we have in these solutions of tungsten a new and exceedingly delicate test for gold. The reaction page 6 also of these oxides of tungsten with silver and mercury is similar to that of the oxide of tin.

"But, interesting as it is to trace out all these analogies between two metals having so great physical differences of constitution as tin and tungsten, belonging, too, to separate isomorphous families, the most important to us is this property of tungsten before instanced—that of substituting tin in the compound called Purple of Cassius, this substance being largely used in the colouring of porcelain. It can be produced in its greatest purity by the method first used for its production, by boiling ordinary tungstate of soda with weak acetic acid, adding hydro chloric acid to the hot solution and deoxidizing the tungstic acid by zinc; the clear blue solution is then poured off and the chloride of gold added; the precepitate when washed is the new compound.

"The following is a brief outline of the method that was found most successful in extracting the tungstic acid in a pure state from the quartziferous ore :—The ore is finely pulverized, water is then poured upon it and the mixture well stirred, and allowed to rest for ten minutes; the liquid and suspended matters are then poured off; the liquid is allowed to get perfectly clear, when it is poured carefully off from the deposit. The fine powder so obtained is then treated with ordinary muriatic acid, and the mixture raised nearly to boiling and kept at this temperature for nearly half-an-hour; the white color of the mineral will then have changed to a perfect yellow, from the liberation of the insoluble acid; the soluble substances are then washed away by frequent decantation. Any of the ordinary soluble tungsten salts are then produced by gently warming the mixture of quartz and tungstic acid with the solutions of the carbonates of their bases. Several of the combinations and salts of tungstic acid above alluded to were represented in the Otogo Geological Museum along with the other Chemical products manufactured from the native minerals of Otago."

It will be seen from the above quotations that Mr. Skey's researches were most satisfactory in their results. The existence of the ore in a lode was not then known.

Not the least important feature of the metal tungsten, is its value as an alloy of steel. Steel, it is well-known, is fast superseding iron. If the last 50 years' period has been the "iron age," the next 50 years will likely be the steel age. By the Bessemer process alone, over half a million tons of steel are turned out every year; consequently anything tending to improve steel must be of great value.

A very able and exhaustive work on "Steel, its history, manufacture, and use," has been written by J. S. Jeans, Secretary to the Iron and Steel Institute. In the preface he states : "That the volume is designed to aid in placing within easy reach of the manufacturers and users of steel, the most recent, as well as the most authoritative notabilia relative to that metal." The book was published so late as 1880, and the following interesting account of tungsten steel is given in page 529 : "Various patents have been taken out for the use of tungsten in the manufacture of cast steel, and at several works, both in England and on the Continent, steel containing sometimes as much as 8 per cent, of tungsten is produced. An elaborate series of experiments has been made at the Royal Iron Foundry, Berlin, on the alloys of iron and page 7 tungsten with the most satisfactory results. Mayer, of Leoben, Styria, is assigned the credit of having first applied tungsten to cast steel, on a large scale, and owing to the success which he attained, tungsten steel has been declared to be of the highest quality in respect to fineness of grain, uniformity of structure, hardness, toughness, strength, and durability. By melting tungsten and iron together, it is possible to obtain a steel much harder than one with carbon alone. For uses which require a special degree of hardness, a steel rich in tungsten, called 'special steel,' is frequently employed. Thus, a fine Sheffield steel for lathe tools, according to an analysis made by Baron Barnekow, in the laboratory of the Stockholm School of Mines, contained 9.3 per cent, of tungsten and 0.7 per cent, of siliceum, with only 0.6 per cent, of carbon. This steel, which is used without being tempered for turning cylinders of hard cast iron, is of sufficient hardness to scratch glass, and yet, it is not fragile, for great difficulty is experinced in breaking a ¾ inch square bar. Tungsten is added for obtaining not only a steel of great hardness, but one of moderate hardness, combined with high ductile capacity, and suitable for the tubes of cast-iron cannons. According to M. Le Guen, tungsten increases the hardness of steel, and up to a certain point its tenacity also. Mushet's patent tungsten steel is manufactured at the works of Wund and Co., at Buckaw, near Magdeburg, in Prussia, and in Hanover. The magnets used at Siemen's telegraphic works in Berlin, are also said to be made of this steel. Tools made of tungsten steel, in use for planing and other machines, are reported to stand longer than those made from the best Sheffield cast steel. A special steel, patented in England, August 10th, 1872, by H. A. Levallois, of Paris, is an alloy containing tungsten and nickel in various proportions, and claims to be less liable to oxidize or rust than ordinary steel. C. W. L. Bierman, of Hanover, manufactures alloys of cast iron and steel containing from 20 to 50 per cent, of tungsten, in ingots, which are sold for mixing with, and so introducing any desired percentage of tugsten into iron or steel."

The following is taken from a late number of the Year Book of Facts :—"By the order of the French Minister of War, a series of experiments has been instituted to determine the influence produced by tungsten upon the qualities of bronze, cast iron, and steel. Caron, who carried out the experiments, reported that the addition of tungsten to cast iron was found to increase both the hardness and tenacity in about the same ratio with the quantity of tungsten added. Even a small percentage, not exceeding one per cent., was found to exert a marked influence, the grain of the iron becoming regular, fine, and grayish, and the fracture showing great homogeneity. The addition of tungsten to steel was found always to increase both its hardness and tenacity. In conclusion, Caron confidently recommended the employment of tungsten to improve the quality of steel, and shows that with tungsten at 3.70 francs the kilogramme, the price of steel would be increased by only seven or eight francs per 100 kilogrammes."

The reference here to the price of tungsten indicates it to be worth about £6150 per ton in France.

Fownes' Inorganic Chemistry, page 482, "Steel alloyed with tungsten acquires an extraordinary degree of hardness. Wotz, or Indian steel, page 8 from which swords are made, contains tungsten. Tungsten has also a remarkable effect on steel in increasing its power in retaining magnetism. A horseshoe magnet of ordinary steel, weighing 2lbs, will not carry more than 7lbs weight. Seimens, the great electrician, says a magnet of that weight (2lbs), if alloyed with tungsten will suspend 20lbs. In view of the important part played by magnets in the generation of electricity, and the application of it to so many useful purposes this is not the least important feature of the metal tungsten.

The latest Supplement recently published of Ure's Dictionary says :—"A patent has been obtained for the manufacture of metallic alloys by Mr. Roxland. Steel of very superior quality, manufactured under this patent, is now coming extensively into use. In Germany it is prepared by simply melting with cast steel, or even with iron only, either metallic tungsten or an alloy of tungsten from two to five per cent. The steel obtained works exceedingly well under the hammer. It is very hard and fine-grained, and for tenacity and density is superior to any other steel made."

The same dictionary, after giving the chemical composition of tungstate of soda, and referring to its use for dyeing, for the making of tungstate of Barytes, and of lead, to be used as pigments, says :—"Still more recently, it has been found to be valuable and preferable to any other substance for rendering fabrics non-inflammable so as to prevent the terrible accidents constantly occurring from the burning of ladies' dresses. For this, purpose a patent has been obtained by Messrs. Versmann and Oppenheim. Metallic tungsten is also used for the manufacture of brittania metal, by alloying with copper and tin. By this useful application this metal has already become a desideratum." These are the facts as stated in Ure's Dictionary, one of the most reliable works published.

In a Manual on Metallurgy, published in 1874 by W. H. Greenwood, F.C.S., the following occurs at page 53, paragraph 65:—"Tungsten reduced from tungstic acid in the presence of iron readily alloys with the latter. Thus, when gray iron is heated to a high temperature along with tungstic acid, the graphet of the pig iron, by combination with the oxygen of the tungstic acid, reduces the metal, which alloys with the iron and produces an exceedingly hard, fine-grained, and almost silvery-white steel, which is more or less malleable according to the quantity of tungsten present."

In Engineering Facts for 1868, page 333, it is stated :—"That which is already known of tungsten proves that it exerts great influence on steel. The price of tungsten is somewhat high on account of its comparative scarceness in nature. On the Continent it is said to make puddled steel equal to cast steel, and so hard as to be suitable for files, saws, edge tools, &c. For wheel tires, from 2 to 3 per cent, of tungsten has been found to answer best. For files, saws, &c., from 2½ to 4 per cent. For dies, punches, bushes, &c., from 4 to 7½ per cent."

The Scientific Review of August, 1868, says:—"If there is one subject more than another attracting and requiring attention at the present time, it is the alloys of tungsten and steel."

The Quarterly Journal of Science says :—"Attention is being directed to the combination of tungsten with steel, and the adaptation of tungstate page 9 of soda as a mordant, and the use of tungsten as an alloy. Pig-iron made at Brest, containing 2 per cent, of tungsten, shows an augmentation of resistance equal to 68 kilogrammes per square centimetre. Numerous other tests proving equally favourable to this new alloy of tungsten and iron have been made."

Millen's chemistry, pages 647 and 652, has the following—"When tungsten is alloyed in certain proportion, it yields steel of remarkable hardness. Small quantities of tungstate of lime (scheelite) is found in Germany. Tungsten is always estimated in the form of tungstic acid, 100 grains of which contain 79.32 of the metal."

It will be seen from these quotations that there is a remarkable unanimity of opinion as to the value and importance of this metal which is found so plentifully in the scheelite lode at Lake Wakatipu. One striking feature is the variety of products that can be extracted from the ore, I mean products of economic value, for which there is evidently a large market with a limited supply. Iron and steel are elements of such extraordinary importance to civilization, that any agent capable of improving them must necessarily be applied. It will also be observed that tungstate of soda—a substance that can be made from scheelite at a very small cost, has the power of resisting fire. There is possibly no limit to the uses to which this material may be put. Fire-proof cloth is already in the market, fire-proof paint, and fire-proof paper. Fireproof roofing for wooden houses would find a large and ready market in the Colonies. The following is a significant advertisement by a London firm :—"Frederick Versmann, 7 Bury Court, St. Mary's Axe, London.—Scheelite ore colours; tunsgate of soda—ladies antiflammable life preserver." Another advertisement is "Briggs and Co., Great Peter St., Westminster.—The ladies' life preserver from fire.—Ladies dresses and other textiles steeped in a solution of this compound are rendered non-inflammable, without injury to texture, colour, or appearance."