Ankerites from the Northumberland coalfield were first described, with chemical analyses, some ten years ago (Hawkes and Smythe, 1935), when it was found that examples from veins exposed on the coast near Hartley and from sludge from nearby coal-washeries showed a remarkable uniformity in composition. The operations of the collieries concerned cover an area roughly 6 × 6 miles, and range from the Beaumont to the High Main Seam. In order to ascertain whether this uniformity is maintained over a wider area, five additional samples of ankerite from veinlets in rocks of Coal Measure age, and one from partings in the Lower Carboniferous Scremerston coal have been examined. The Coal Measure rocks cut by the veinlets have been proved to contain substantial proportions of ferriferous carbonates, while for comparative purposes two examples of rocks of similar age with carbonate but unaccompanied by ankerite veinlets have been investigated. The range in composition of ankerites in the coalfield has proved to be small.

The contour and dimensions of a typical blast furnace are shown in fig. 1. The shell of the furnace consists of riveted steel plates, inside which is a lining of firebricks varying in thickness about 2–3½ feet. Molten iron collects in the crucible or hearth at the bottom of the furnace and is periodically run off through a hole in the side of the furnace known as the tap-hole. The hearth is lined with firebrick both around the sides and along the floor, the total thickness of brickwork below the hearth in fig. 1 being 3 feet 9 inches.

Cuspidine was first described by Scacchi (1876) in the ejected blocks of metamorphosed limestone at Vesuvius, but a detailed and systematic morphological description of well-terminated crystals was given first by vom Rath (1883) from material at Cozzolino in Resina, Vesuvius. The monoclinic character of the spear-shaped crystals was then established with a:b:c = 0·7243:1:1·9342, β = 89° 22′, and twins on (100) giving = 1° 16′. Scacchi (in Arzruni, 1877) had earlier indicated the possibility that cuspidine he had described as orthorhombic was monoclinic and twinned when he recognized a re-entrant angle of 178° 42′ on the cleavage truncating the acute ends of the crystals.

In the description of an improved polarizing microscope, recently published by the present authors, provision was made for the use of polarizing film in place of calcite prisms, and the consequent changes in the design of the substage and tube were discussed. The model then described was, however, of smaller size than is required for some patterns of Fedorov stage now in use, and a larger stand wan under consideration. For technical reasons this could not be produced at the same time as the smaller instrument, and it was therefore necessary to postpone the description which forms the subject of the present supplementary paper. The changes involved are mainly dimensional, the optical and manipulative arrangements being in principle the same as in the smaller model, but the general standard of equipment in details such as stage racks, ball-bearing stage, and interchangeable bodies is on a scale corresponding with that in the largest existing types of stand.

While studying some of the early works on minerals I came across an obvious difficulty: several minerals, amongst which lapis-lazuli is the most startling, are described in Latin as flavus, yellow or flaxen-coloured, not blue. This error has been copied into a book in English. The solution is less obvious than the difficulty, and it may therefore be worth while to put it on record for other workers on similar lines.

Pyrophanite was recorded by one of us in a recent paper as one of the minerals occurring at the Benallt manganese mine in the vein from which material for the chemical analyses of the new manganese-rich chlorite, pennantite, was separated. As this was only the third record of pyrophanite in the world it seems necessary to give, very briefly, the evidence for its identification.

The crystals of artificial cassiterite, described below, were produced by volatilization of South African low-grade tin ores. In the sinter-pot method employed, air was blown through a charge of alternate layers of coke and of a 12 % metallic tin concentrate mixed with fine coke. This charge was placed above a basal layer of previously ignited coal. Occasionally sodium chloride was mixed with the concentrate to remove tin as chloride as well as oxide fume. The air-flow was carefully controlled to prevent slagging and was maintained until the evolution of copious fumes of tin oxide, and at times of chloride, ceased.

Optical pyrometer readings on the charges during the experiments gave temperatures of 1050°C. approximately, but it is certain that this value is a grave under-estimate of the actual temperatures in the interior of the sinter-pot.

A new tin mineral, which has been given the name ‘nigerite’, was discovered in June 1944 during au investigation of the tin-bearing pegmatites of Kabba Province, central Nigeria. The chemical and physical properties of nigerite have been determined by F. A. Bannister, M. H. Hey, and H. P. Stadler, and their results will be published in the next number of this Magazine. Dr. Hey's analysis shows SnO2 25·33, Al2O3 50·91, Fe2O3 11·90, ZnO 4·51 %, &c., and the unit-cell contents are given by the formula (Zn,Mg,Fe″)(Sn,Zn)2(Al,Fe‴)12O22(OH)2.