143

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engines and the wmch engines are supplied with steam from two 16 nominal horse-power boilers carrying 1401b. pressure. It was contemplated putting in one 30-horse-power boile? but he difficulty of transporting up-country prevented this. The boilers are on a principle specially designed for dredges where dirty water has to be used. They are what may be called loco-tubular boilers wnh circular furnaces. The furnace end is much larger in diameter than the other, the object being to reduce botn weight of boiler and contained water, as well as to allow for the unequal expansion which comes on the Cornish type of boiler when fired straight through without returning sts^LtighTEngSd. 611811168 an<l bOilerß haVe been impOTted from S M»i, " f Th i e COS f ° f fud iS US n UaU ? hig} \ in . oufc -° f places, and it is found advisable to use the highest class of engines and boilers obtainable. These boilers are also specially adapted to burn th* local fuel which is usually a low class of lignite. The elevator consists of a long steel ladder TrtT Z m °! * b *1 the u tOp ' and laUlC6d at the Sides below the box to form a Ser.' It is fixed to the stern of the dredge by a pivoting-shaft, and supported by four steel-wire ropes' leading to two masts of 40 ft. high, set in the centre of the dredge, and it is stayed sidewaysTv two hght steel pipes from the stern corners of the dredge up to° about 30 ft. from the upper end At each end of tne elevator there is a pair of light seven-sided tumblers, over which a continuous h M wl bu , ck f , work ' , and lnslde th e upper portion of the ladder there are six pairs of rollers on which the buckets travel, also six pairs of rollers on the lower side down which the returning empty -buckets travel The elevator is driven from the lower tumbler by a train of gearing connected to the mam gearing by means of a belt. The whole of the machinery, with the exclptSnofTheTentnwi pump air-pump and condenser, is above deck, under the eye of the driver, and every pointk considered to make the machinery convenient to work, and accessible in case of repairs '• Ihe dirt after being lifted is discharged into a double shoot made of steel, heavily barred with stael bars Prom this it is again discharged into two revolving steel cylinders, each 16 ft 6in long by 4 ft. diameter, and perforated for about 12 ft. of their lenjth with holes ranging from In! at the upper end to* in. at the lower. These screens are set with a fall towards the stern ofthe dredge, and there is a perforated pipe through each cylinder near the top. From these pipes a continuous shower of water falls upon the washdirt, which is tumbled about as it passes down through the cylinders. The fine dirt, sand, and gold is all washed through the perforations on to S bles below while the coarser dirt and stones pass out at the lower end into the tailings elevator. The gold-saving tables consist of a series of four boxes, each 3 ft. wide and 13 ft long on both sides of the dredge. These boxes are made of steel, thick set parallelTnri secured together the one being stepped below the other to the"fall or P p tc of the screens, and each set of boxes has a fall from the centre towards the sides of the dredge where they again discharge into the tail-shoots, 2 ft. wide, leading aft, where they deliver the fine'dirt behind " The boxes or tables are covered with cocoanut-matting, in lengths of 4 ft., for convenience in lifting and washing. Calico is laid on the bottom of the boxes to catch any fine °o d at m pass through the cocoanut-matting, and the matting is held down by strips of wood la°d edges, and wedged by wooden wedges, or clips, along the side-divisions of the boxes. The mats on tne upper end of the go d-saving tables are usually lifted every morning, and sometimes oftener if the dredge is getting a large amount of gold. They are washed in large troughs, and he Save! sand, and gold is then streamed down on either plush, baize, blanket, or cocoanut-mSnl tn a box about 12 ft. long and 20 m. wide. After this nothing but the gold and heavier pcrtiSns of the sands remain, and this is taken out by either panning it off in a dish or amal™ ,„„ h usually the former. The coarser dirt and "stones, after passing out of the °4voS cyln de ' are discharged into the tailings-elevator, lifted up and stacked behind the dredge, at such a distance that the stern will not touch or ground upon them. The dredge will work its wlyTnto the bank from the river, stacking its tailings to a height of 40 ft. behind it, forming its own dam or paddock which will be raised by letting a stream of water flow into it, and thus raise the dredge to any leve required to work the ground. It has to work almost con inuousy night and day, and in all weathers, and the whole of the machinery, with the exception Sl?elXc S Ugh?. tailm^-eleVator ' will be comfortably hoLed in, and HghtEt night "This dredge would be capable of lifting and treating about 19,800 cubic yards of travel per week rf the buckets could be kept continually running full, but allowing 25 per oeS o loss for buckets coming up not full, the dirt lifted would be, say, 14,800 cubic yards The working-expenses will be: Wages, £23; fuel, £16; wear-and-tear to machinery. £?2 •<S was c and sundries, £2: m all £53 a week. This would make the average cost of lifting and ltrltine a cubic yard of dirt something under Id. ° creating i-« " l \ iS "^ c . restin S *°, n ° te the Wft y in which che tailings from a dredge will stack up under different conditions. A dredge with a single sluice-box, into which the whole of the Sashdir is discharged, will require about 20 per cent, more room to stack the tailings tbln they formerly occupied; but one fitted with a revolving screen will require fully 33 nef cent mni room due to the fact that the fine dirt is separated from the coarse, and only gets parSv mixed again when discharged at the stern by the two shoots; while the tailings from HredS with a tailings-elevator require nearly 50 per cent, more space to stack. In this case the fife dirt, and a 1 tha passes hrough the perforations in the revolving screen, is delivered close under the stern of the dredge, and settles on the bottom, while the coarse dirt Tnd stones are carried up the c evator and stacked on top of the fine stuff, which gets no chance „ c " mterstices betw een are not filled, consequently much more room if "As illustrating the state of perfection to which the New Zealand type of dredges has been brought, the largest of them are being worked by only two men per eight-hour slfft, and one