Page:Popular Science Monthly Volume 37.djvu/185

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do not deplore this sacrifice of the best elements in human life, but on the contrary hold up as an ideal for whose protection and extension the national policy should chiefly exert itself, that very industrialism under which this sacrifice takes place. Food, clothing, shelter, and the household goods and gods have value only as they minister to human life. But, by a curious inversion, these things are now held to be of greater importance than the life which they were originally intended to conserve. The savagery of modern times wears a different garb from that of the past, but it is none the less of the essence.

But to return to the acid-worker, for his besmeared face and irritated eyes are still before us. The three windows of the little room in which he works are kept open winter and summer, in the hope of diluting the poisonous fumes—a clumsy arrangement at the best. It would be quite possible to have the atmosphere, if not entirely wholesome, at least comparatively so, by placing the acid bath directly under a good flue or exhaust, so that the escaping fumes should be drawn off artificially. Every chemist's laboratory contains such an evaporating closet.

The hydrofluoric acid employed for etching is a chemical unfamiliar to the majority of people. Its corrosive character, and the fact that it has few common uses, preclude such an acquaintance. The source of the acid, however, the mineral fluor-spar, is quite abundant in nature. It is so beautiful a mineral, occurring in nearly all the colors of the rainbow and in well-defined cubes and octahedra, that it is given a prominent place in all mineralogical cabinets. It is, therefore, probably better known than the acid derived from it. The mineral itself is a fluoride of lime, and, when treated with oil of vitriol, gives off fumes of hydrofluoric acid. These are exceedingly soluble in water, forming the ordinary hydrofluoric acid of commerce. The bath used in etching the globes contains in addition a certain amount of oil of vitriol. Glass plunged into such a bath will have its surface eaten away, but will remain transparent. The wooden trough containing the bath is from three to four feet long, and less than a square foot in cross-section. Half a dozen globes are treated at a time. They are mounted on a steel axle, separated from each other by washers cut out of thick rubber. These serve the double purpose of protecting the glass from injury and of keeping the liquid out of the interior. When the axle is put in place in the trough, the globes are about half submerged in the bath. The axle is given a slow rotary motion, and, at the end of about fifteen minutes, the etching is completed. The globes are removed from the bath, and another axle carrying six fresh globes put in its place. The chemical action consists in the formation of gaseous fluoride of silicon, the bath affording the fluorine and the glass the silicon. It is