Whilst these systems were exclusively supplied with rollers made of granite or hard porcelain up to a few years ago, it has been found that good results are obtained by the use of cast rollers, and they have been for some time employed on machines of three, four and five rollers. (Figs. 38, 40, 41 a-c.) In consequence of the non-porous surface of these steel rollers, it is possible to grind to a finest powder, merely in one operation, without passing the chocolate through the machine several times; and the so-called “Burning” of masses which have not been properly mixed cannot arise in this case, though it is true that the apparatus must be provided with water cooling arrangements to avoid a too excessive heat. They are specially adapted to the preparation of the more ordinary qualities, and are even occasionally employed for finer chocolates, for obviously these must be again submitted to a rolling process, when granite or porcelain rollers are preferred. [Illustration: Fig. 41 c.] For this reason the 6, 9 or even 12 roller mills have been more discarded since the last grinding process has been performed by granite rollers (cold process). In order to avoid the disadvantages of the pulley drive, it is in certain cases advisable to drive each machine direct from an electric motor. Fig. 42 illustrates a refining machine driven in this manner. [Illustration: Fig. 42.] c) ~Proportions for mixing cacao mass, sugar and spices.~ The relative proportions of cacao, sugar, and spices, as well as of starch as in the manufacture of the cheaper sorts, vary considerably. Generally speaking 50 or 60 parts of sugar are added for 50 or 40 parts of cacao mass; the following are a few formulae applicable for the production of those kinds of pure chocolate that are most used. A. Hygienic chocolate. Cacao mass } Powdered sugar} equal parts of each. B. Spiced chocolate. a) Cacao mass 4 kg Sugar 6 kg Cinnamon 72 g Cloves 38 g Cardamoms 16 g b) Cacao mass 4 kg Sugar 6 kg Cinnamon 130 g Coriander 8 g Cloves 88 g Oil of lemons 2 g Cardamoms 16 g c) Cacao mass 5 kg Sugar 5 kg Cloves 80 g Cinnamon 220 g Mace 8 g d) Cacao mass 5 kg Sugar 5 kg Cinnamon 100 g Vanilla 100 g or Vanillin 2·5 g Mace 2 g Cardamoms 4·2 g e) ~Spanish spiced chocolate.~ Cacao mass 5 kg Sugar 5 kg Cinnamon 116 g Cloves 50 g Cardamoms 82 g Mace 44 g Vanilla 40 g or Vanillin 1 g Oil of lemons 1 g C. Vanilla chocolates. a) Cacao mass 5 kg Sugar 5 kg Cinnamon 160 g Vanilla 50 g (or Vanillin 1·2 g)