GLASS-MAKING. 



173 



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, cloth- 

 ing, 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 escap- 

 ing fumes should be drawn off artificially. Every chemist's labo- 

 ratory contains such an evaporating closet. 



The hydrofluoric acid employed for etching is a chemical un- 

 familiar to the majority of people. Its corrosive character, and 

 the fact that it has few common uses, preclude such an acquaint- 

 ance. 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 mineral- 

 ogical 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 ordi- 

 nary 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 pro- 

 tecting 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 etch- 

 ing is completed. The globes are removed from the bath, and an- 

 other axle carrying six fresh globes put in its place. The chemi- 

 cal action consists in the formation of gaseous fluoride of silicon, 

 the bath affording the fluorine and the glass the silicon. It is 



VOL. XXXVII. — 13 



