Fig. 13 shows a cleansing machine for the same purpose, which has recently become rather popular. Here the dust passing from the sieve is sucked up into a dust chamber, by means of an exhauster, whilst pebbles, blossom fragments, and small beans are separately isolated. The cleansed beans pass likewise under magnetic influence, which removes traces of iron, and finally succeed to the running belting. Often the beans are introduced into an extensive brushing machine before roasting, to cleanse them from dirt etc. These are generally found in such factories as have circular and cylinder roasters with direct heating apparatus. Fig. 13 a shows such a brushing machine for cacao beans. 2. ~Roasting the Beans.~ The cleansed and sorted beans are now subjected to a high temperature, that is to say, they are now roasted. This roasting answers many purposes; 1. The aroma and flavour of the bean is so developed. 2. The starch granules are gelatinised. 3. The herbal constituents are so transformed that the flavour of the beans becomes milder; a distinct improvement. 4. In the consequent drying, the shells are rendered brittle, and more easily removeable. 5. The beans themselves can afterwards be better ground. The roasting of the cacao bean does not demand so high a temperature as that of coffee, to effect the above chemical and physical changes. Experience has shown that the best temperature lies between 130-140 ° C., though deviations from this standard have recently become frequent and considerable, according to the uses for which the cacaos are intended, and roasting has sometimes taken place at a temperature even as low as 100 ° C. [Illustration: Fig. 12.] The process of roasting can be carried out in the roasting drum or machine in a variety of ways, as: 1. Direct roasting over a coal fire, 2. Passing of a hot-air stream over the beans, [Illustration: Fig. 13.] 3. Roasting by means of gas, with compressed air, as far as ~sources of heat~ are concerned; and as regards ~shape of the drum~, it is to be noted that the cylindrical are most in use. The separation of the shells from the kernel was still effected at the beginning of the present century by stirring the beans in water and so detaching the inner coating of the seeds, the method adopted by Weisched (Mitscherlich page 112). Not till this stage had been reached were they subjected to a strong heat, causing the shells to spring off. This method has at the present time only historical interest, for the so-called roasting drums, as used in the preparation of coffee, are now universal. [Illustration: Fig. 13a.]