Page:Popular Science Monthly Volume 31.djvu/657

Rh may be desired. The conical corks are used when the corking is done by hand, the cylindrical ones when it is done by machinery. Other machines for punching corks into shape and for grinding them have been tried and discarded. M. Moreau, the inventor of the latter machine, combined with it the idea of cutting a portrait-face on the cork,



so that every house might send out the image of its chief on its wares; but the device has not advanced further than to the stage of a happy thought. Another machine has been invented in which the knife is a rotating disk, self-sharpening, and the cork also turns.

After having been shaped, the corks are washed in water containing oxalic acid or chloride of tin, or are sometimes treated with sulphuric acid. They thus acquire a characteristic salmon tint, and become velvety and soft to the touch. They are then sorted according to size, tested for quality, counted by hand or by the aid of special machines, and packed in sacks containing from fifteen to thirty thousand each.

The quality most sought in a good cork is impermeability to gases and liquids. The bark may be tested for this quality before making up, by means of an apparatus invented by M. Salleron, in which it is subjected to the pressure of a liquid which has already been compressed in a hydraulic machine. A cork of the first quality should stand a pressure of several atmospheres without absorbing any of the