sweeping off all the seed when it has been sufficiently bruised. The pres sure and action of these rakes is adjusted by means of wooden springs, which cannot be easily and distinctly represented by any figure. The oblique position of the rakes (the outer point going foremost) causes them to shove the grain inwards, or toward the centre, and at the same time to turn it over somewhat in the manner as the mould-board of a plough shoves the earth to the right hand, and partly turns it over. Some mills have but one sweeper; and indeed there is great variety in the form and i construction of this part of the machinery. Fig. 464, profile of the pestle-frame. 1, section of the horizontal shaft. 2, three wipers for lifting the pestles. 3, little wheel of 28 teeth for giving motion to the spatula. A, another wheel which is driven by it, having 20 teeth. 5, horizontal axle of ditto. 6, another wheel on the same axle, having 13 teeth. 7, a wheel upon the upper end of the spindle, having 12 teeth. 8, two guides, in which the spindle turns freely, and so that it can be shifted higher and lower. 9, a lever, movable round the piece No. 14, having a hole in it at 9, through which the spindle passes, turning freely. The spindle has in this place a shoulder, which rests on the border of the hole 9, so that by the motion of this lever the spindle may be disengaged from the wheel-werk at pleasure; this motion is given to it by means of the lever 10, 10, movable round its middle. The workman employed at the chauffer pulls at the rope 10, 11, and thus disengages the spindle and spatula. 11, a pestle seen sidewise. 12, the left of ditto. 13, the upper rails, marked No 3, in fig. 460. 14, the rail marked No. 5, in fig. 460. To this are fixed the detents, which serve to stop and hold up the pestles. 15, a detent, which is moved by a rope at its outer end. 16, a bracket behind the pestle, having a pulley through which passes the rope going to the detent 15. 17, the said pulley. 18, the rope at the workman's hand, passing through the pulley 17, and fixed to the end of the detent 15. This detent naturally hangs perpendicular by its own weight. When the workman wants to stop a pestle, he pulls at the rope 18, during the rise of the pestle. When this is at its greatest height, the detent is horizontal, and prevents the pestle from falling, by means of a pin projecting from the side of the pestle, which rests upon the detent, the detent itself being held in that position by hitching the loop of the rope upon a pin at the workman's hand. 19, the two lower rails, marked No. 10, fig. 460. 20, great wooden, and sometimes stone, block, in which the mortars are formed, marked No. 21, fig. 460. 21, vessel placed below the press-boxes for receiving the oil. 22, chauffer, or little furnace, for warming the bruised grain. 23, backet in the front of the chauffer, tapering downwards, and opening below in a narrow slit. The hair-bags on which the grain is to be pressed after it has been warmed in the chauffer, are filled by placing them in this backet. The grain is lifted out of the chauffer with a ladle, and put into these bags; and a good quantity of oil runs from it through the slit at the bottom into a vessel set to receive it. 24, the spatula attached to the lower end of the spindle, and turning round among the grain in the chauffer-pan, and thus preventing it from sticking to the bottom or sides, and getting too much heat. The first part of the process is bruising the seed under the runner-stones; that this may be more expeditiously done, one of the runners is set about two-thirds of its own thickness nearer the shaft than the other; thus they have different treads, and the grain, which is a little heaped towards the centre, is thus bruised by both. The inner rake gathers it up under the outer stone into a ridge, of which the section is represented in fig. 465; the stone passes over it, and flattens it. It is gathered up again into a ridge, of the form of fig. 466, under the inner stone by the outer rake, which consists of two parts; the outer part presses close on the wooden border which surrounds the nether stone, and shoves the seed obliquely inwards, while the inner part of this rake gathers up what has spread towards the centre. The other rake has a joint near the middle of its length, by which the outer half of it can be raised from the nether stone, while the inner half continues pressing on it, and thus scrapes off the moist paste. When the seed is sufficiently bruised, the miller lets down the outer end of the rake; this immediately gathers the whole paste, and shoves it obliquely outwards to the wooden rim, where it is at last, brought to a part that is left unbearded, and it falls through into troughs placed to receive it. These troughs have holes in the bottom, through which the oil drips all the time of the operation. This part of the oil is directed into a particular cistern, being considered as the purest of the whole, having been obtained without pressure, by the mere breaking of the hull of the seed, In some mills this operation is expedited, and a much greater quantity of this best oil is obtained, by having the bed of masonry which supports the legger formed into a little furnace, and gently heated; but the utmost care is necessary to prevent the heat from becoming considerable. This enabling the oil to dissolve more of the fermentable substance of the seed, exposes the oil to the risk of growing soon very rancid; and in general it is thought a hazardous practice, and the oil does not bring so high a price. When the paste comes from under the stones, it is put into the hair-bags, and subjected to the first pressing. The oil thus obtained is also esteemed of the first quality, scarcely inferior to the former, and is kept apart (the great oil-cistern being divided into several portions by partitions.) The oil-cakes of this pressing are taken out of the bags, broken to pieces, and put into mortars for the first stamping. · COLOUR AND INDIGO MILLS. THE reducing of earths, vegetable substances, and metallic oxyds to an impalpable powder, is still in a great degree effected by manual labour, by moving a heavy stone with a smooth surface, called a muller, upon a slab of the same material. To effect this work upon a larger scale, and to secure the workman from the ill effects of the poisonous and noxious vapours of the paint, which is not unfrequently ground with litharge of lead, Mr. Rawlinson, of Derby, has invented a machine which we here describe. It is repre sented in fig. 467. A, the roller, or cylinder, made of any kind of black marble. Black marble is esteemed the best, because it is hardest, and takes the best polish. B, the concave muller, covering one-third of the roller, and of the same material, fixed in a wooden frame b, which is hung to the frame E at ii. C is a piece of iron, about an inch broad, to keep the muller steady, and is fixed to the frame with a joint at f. The small binding screw with a fly-nut, which passes through the centre of the iron plate at c, is for the purpose of laying more pressure upon the muller, if required, as well as to keep it steady. D is a taker-off, made of a clock-spring, about half an inch broad, and fixed similar to a frame-saw in an iron frame K, in an inclined position to the roller, and turning on pivots at dd. G is a slide-board to draw out occasionally, to clean, &c. if any particles of paint should fall from the roller; it also forms itself for the plate H, to catch the colour as it falls from the taker-off. F is a drawer for the purpose of containing curriers" sharings, which are used for cleaning paint-mills. E is the frame, Previously to putting the colour in the mill, it must be pulverized in a mortar, covered in the manner of the chemists, when they levigate poisonous drugs, or rather in an improved mill, used at Manchester, by Mr. Charles Taylor, for grinding indigo in a dry state, a drawing and description of which is annexed. After undergoing this process of dry-grinding, which is equally necessary for the marble slab now in use, it is mixed with either oil or water, and is with a spatula, of palette-knife, put on the roller, near to the top of the concave muller. Motion being given to the roller, it, without any difficulty, carries the colour under the muller, and in a few revolutions spreads it equally over the surface. When ground sufficiently, it is taken off, both cleanly and expeditiously, by the taker-off described, which, for that purpose, is held against the roller, while the roller is turned the reverse way. The muller only requires to be cleaned when the workman changes the colour, or ceases from the operation; it is then turned back, being hung on pinions to the frames at i i, and is cleaned with a palette-knife or spatula; afterwards a handful of curriers' shavings is held against the roller, which, in two or three revolutions, cleans it effectually. The roller of Mr. Rawlinson's machine is sixteen inches and a half in diameter, and four inches and a half in breadth; and the concave muller which it works against covers onethird of the roller. It is therefore evident, that, with this machine, he has seventy-two square inches of the concave marble muller in constant work on the paint, and that he can bring the paint much oftener under the muller in a given space of time than with the common pebble muller, which, being seldom more than four inches in diameter, has scarcely sixteen square inches at work on the paint, whereas the concave muller has seventy-two. The quantity ground at once in the mill must be regulated by the degree of fineness of which it is required, that which is the finest requiring the smallest quantity to be ground at once. The time requisite for grinding is also dependant upon the state of fineness; but Mr. Rawlinson observes, that his colour-grinder has ground the quantity of colour which used to serve him per day in three hours; the colour also was more to his satisfaction, and attended with less waste. When the colour is ground, Mr. Rawlinson recommends, instead of drawing the neck of the bladder up close in the act of tying it, to insert a slender cylindrical stick, and bend the bladder close round it; this, when dry, will form a tube or pipe, through which, when the stick is withdrawn, the colour may be squeezed as wanted, and the neck again closed by replacing the stick. This is not only a neater and much more cleanly mode than the one usually adopted, that of perforating the bladder, and stopping the hole with a nail, or, what is more common, leaving it open, to the detriment of the colour; but the bladder, not being injured, may be repeatedly used for fresh quantities of colour. The barrel of a quill may be inserted in the neck of the bladder, as a substitute for the stick, and the end being cut off, may be closed by a small piece of wood. In order to make the whole of the process of colour-grinding complete, we shall here insert a description of the indigo-mill used by Mr. Charles Taylor, of Manchester, for grinding indigo in a dry state, which may with equal advantage be similarly employed for colours. It is represented in figs. 468 and 468*. L, fig. 468, represents a mortar, made of marble or hard stone; one made in the common way will answer. M. a muller, or grinder, nearly in the form of a pear; in the upper part of which an iron axis is firmly fixed, which axis at the parts N N turns in grooves or slits, cut in two pieces of oak, projecting horizontally from a wall, and when the axis is at work are secured in the grooves by iron pins O O. P, the handle, which forms a part of the axis, and by which the grinder is worked. Q, the wall in which the oak pieces N N are fixed. R, a weight, which may occasionally be added if more power is wanted. Fig. 468, shows the muller or grinder, with its axis separate from the other machinery; its bottom should be made to fit the mortar. S is a groove cut through the stone. On grinding the indigo, or similar substance, in a dry state, in this mill, the muller being placed in the mortar and secured in the oak pieces by the pins, the indigo to be ground is thrown above the muller into the mortar; on turning the handle of the axis, the indigo, in lumps, falls into the groove cut through the muller, and is thence drawn under the action of the muller, and propelled to its outer edge within the mortar, whence the coarser particles again fall into the groove of the muller and are again ground under it; which operation is continued till the whole of it is ground to an impalpable powder; the muller is then easily removed, and the colour taken out. A wood cover in halves, with a hole for the axis, is usually placed upon the mortar, during the operation, to prevent any loss to the colour, or bad effects to the operator. POTTERY. THE clays best adapted for the manufacture of earthenware are excavated in Dorsetshire, and the next in quality in Devonshire. The natural compounds, called clays, consist generally of pure clay, or alumine, combined with either silex or lime, and sometimes magnesia, and the oxyd of iron. The presence of the magnesia may easily be detected by its imparting a soapy feel; and the iron by the clay burning to different shades of red, proportionate to the quantity it contains. The magnesia has obtained the name of soap-rock, and a marked variety of it steatite. The clay is first put into a trough about five feet long, by three wide, and 24 deep, with a certain proportion of water, and subjected to the process called blunging, which is obviously akin to blending, or mixing. This is performed with a long piece of wood formed in the shape of a blade at one end, and with a cross-handle at the other. The bladed end is put into the trough, and moved backwards and forwards, up and |