In this process, by the mere act of grinding, the miracle is performed of converting the brittle fragments of the cacao bean into a chocolate-coloured fluid. Half of the cacao bean is fat, and the grinding breaks up the cells and liberates the fat, which at blood heat melts to an oil. Any of the various machines used in the industries for grinding might be used, but a special type of mill has been devised for the purpose. In the grinding room of a cocoa factory one becomes almost hypnotised by a hundred of these circular mill-stones that rotate incessantly day and night. In Messrs. Fry's factory the "giddy motion of the whirling mill" is very much increased by a number of magnificent horizontal driving wheels, each some 20 feet in diameter, which form, as it were, a revolving ceiling to the room. Your fascinated gaze beholds "two or three vast circles, that have their revolving satellites like moons, each on its own axis, and each governed by master wheels. Watch them for any length of time and you might find yourself presently going round and round with them until you whirled yourself out of existence, like the gyrating maiden in the fairy tale." In this type of grinding machine one mill stone rotates on a fixed stone. The cacao nib falls from a hopper through a hole in the centre of the upper stone and, owing to the manner in which grooves are cut in the two surfaces in contact, is gradually dragged between the stones. The grooves are so cut in the two stones that they point in opposite directions, and as the one stone revolves on the other, a slicing or shearing action is produced. The friction, due to the slicing and shearing of the nib, keeps the stones hot, and they become sufficiently warm to melt the fat in the ground nib, so that there oozes from the outer edge of the bottom or fixed stone a more or less viscous liquid or paste. This finely ground nib is known as "mass." It is simply liquified cacao bean, and solidifies on cooling to a chocolate coloured block. [Illustration: SECTION THROUGH GRINDING STONES.] This "mass" may be used for the production of either cocoa or chocolate. When part of the fat (cacao butter) is _taken away_ the residue may be made to yield cocoa. When sugar and cacao butter are _added_ it yields eating chocolate. Thus the two industries are seen to be inter-dependent, the cacao butter which is pressed out of the mass in the manufacture of cocoa being used up in the production of chocolate. The manufacture of cocoa will first be considered. (_i_) _Pressing out the excess of Butter._