ELEMENTS OF MATERIA MEDICA.
582
then drawn off and put into a copper boiler, where it is evaporated andshimmed. It is then conveyed through a series of boilers, the last ofwhich is called the teache. When it has acquired a proper tenacity andgranular aspect, it is passed into a wooden cooler, where it is allowed tocrystallize or grain. The concrete sugar is then placed in casks (usuallysugar hogsheads) with holes in the bottom, each of which is partiallyclosed by the stalk of a plantain leaf. Here the sugar is allowed todrain for three or four weeks. It is then packed in hogsheads and sentto this country under the name of muscovado or raw sugar. The un-crystallized portion is termed molasses ; it is brought to England incasks. In Jamaica a mixture of w'ater and molasses, with the skimmingsof the clarifier and evaporating coppers, is fermented, and a vinousliquid thereby obtained, which, by distillation and rectification, yieldsrum (spiritus sacchari, vide pp. 196, 199, 204).
Sugar Refining. —Raw sugar contains several impurities, from whichit is freed by refining. The eye recognizes the colouring matter. In anaqueous solution of raw sugar, lime is detected by oxalic acid, whichthrows down the white oxalate of lime ; tannic acid by the dark colourproduced on the addition of sesquichloride of iron, and by the precipi-tate formed by gelatin; glutinous and gummy matter by diacetate oflead ; and free acid by litmus. By keeping, strong raw sugar becomesweak, that is, soft, clammy and gummy. This change Mr. Daniell[Quart. Journ. of Science, vi. 38) ascribes" to the action of the lime.
The following is an outline of the refining method which I saw'practised at a large sugar-house in town:—Raw sugar is dissolved inwater by the aid of steam (this process is called a blow-up). The liquidis then heated with bullock’s blood (technically called spice), and some-times with hydrate of alumina (termed finings), and filtered throughcanvas. The clear liquor is allowed to percolate slowly through a bed
View of Two Vacuum-Pans and their subsidiary Apparatus.
a, a, Charging measures, supplied by pipes, which descend from c, c, the liquor cister 0 * ad, d, are the vacuum spheroidal pans, the lower half of each being supplied wlt eletjacket, as a case for the steam. At the sides of the neck of each pan are a barom ^and thermometer. Below the neck, and just above the horizontal line b, b, IS j.handle of the proof-stick, which appears like a stop-cock. When the sjrup“ sufficiently-concentrated, it is discharged into the heater, e, e.