[Illustration: Fig. 29.] 7. ~Treatment of the Mixture.~ a) Trituration. In describing the mixing machines, we do not intend to enter into details regarding the machines formerly in use, but merely to give a brief outline of the principles illustrated in their construction. Trituration was formerly produced; 1. by rollers running backwards and forwards on a grinder; 2. by several cones rotating in a circle on a disc-shaped bed; 3. by means of rotating stones running in a trough; 4. by means of several cylindrical rollers; 5. by means of grooved cone moving in a grooved casing.[115] At the present time only the type mentioned under 1. and 4. are in general use. 3. is met with less frequently, and will be described at greater length in a subsequent paragraph. The machines 1. and 3. are put into operation prior to the cylinder rolling mills, which finish off the incorporation of chocolate and sugar and the levigation process only begun in the first-named. The machines constructed in the manner described under 3., to which we now turn, were introduced by G. Hermann of Paris, but are at present almost obsolete. Since they have some historical interest and are typical of the development of the melangeur, we annex a rough sketch showing their general construction in fig. 29. The ellipsoid runners _a_ made of granite work in the trough _i_ which is also of granite and is fitted with the casing _h_. The runners rotate on their axles _b_ so as to move in a circle. The two arms of the axis _b_ have at the centre an elliptical ring with a quadrangular opening, into which fits the similar shaped part of the vertical shaft _c_ fitted with the toothed wheels, _d_ and _d′_, which are set in motion by power transmitted to the shaft and its connections. The arm _b_ has some play downwards, so that it can adjust itself vertically according to the greater or less quantity of material in the mill. The two steel blades, _e_ and _e′_, are shaped to fit the cavity of the trough; being connected with the shaft _c_ they revolve with it and sweep down the cacao mass adhering to the sides of the mill. Between the foundation _k_ and the trough _i_ there is a space _l_ into which steam can be introduced through _f_, the condensed water passing away by _g_.