This structure can be rendered visible by superficial etching with dilute acid; and as the minuter crystals dissolve more quickly than the larger ones, the surface assumes a frosted appearance (moiree metallique).
While the Alps thus constitute the northern boundary of Italy, configuration and internal geography are determined almost entirely by the great chain of the Apennines, which branches off from the Maritime Alps between Nice and Genoa, and, after etching in an unbroken line from the Gulf of Genoa to the Adriatic, turns more to the south, and is continued throughout Central and Southern Italy, of which it forms as it were the back-bone, until it ends in the southernmost extremity of Calabria at Cape Spartivento.
Fluorides can be readily detected by their power of etching glass when warmed with sulphuric acid; or by warming them in a glass tube with concentrated sulphuric acid and holding a moistened glass rod in the mouth of the tube, the water apparently gelatinizes owing to the decomposition of the silicon fluoride formed.
In the 17th and 18th centuries the processes of scratching, engraving and etching were brought to great perfection.
Dark coloured micas are strongly pleochroic. Accurate determinations of the optical orientation, as well as the symmetry of the etching figures on the cleavage planes, seem to suggest that the micas, except muscovite, may be anorthic rather than monoclinic in crystallization.
In some places wood-carving has been brought to considerable perfection; and native artists know how to engrave on metal both by etching and the burin.
These regions present magnificent examples of dry erosion by wind-borne sand, which acts as a powerful sand blast etching away the rocks and producing most beautiful sculpturing.
Wood engraving kept its ground for a considerable period, especially in Germany, but copper in the end supplanted it, and owing to the beauty and clearness of the maps produced by a combination of engraving and etching it still maintains its ground.
Schwanhart of the process of etching on glass by means of hydrofluoric acid, and the rediscovery by J.
Among engravings of the same time are three Madonnas, the apostles Thomas and Paul, a bagpiper and two peasants dancing, and three or four experiments in etching on plates of iron and zinc. In wood-engraving his energies were almost entirely given to bearing a part - which modern research has proved to have been not nearly so large as was traditionally supposed - in the great decorative schemes commanded by the Emperor Max in his own honour, and devised and carried out by a whole corps of men of letters and artists: namely, the Triumphal Gate ..and the Triumphal March or Procession.