THE OTAGO INSTITUTE.

Otago Witness, Issue 1005, 4 March 1871, Page 5

THE OTAGO INSTITUTE.

The following " Description of a simple contrivance for economising the current of the Clutha or Molyneux, and other large rivers, for gold- sluicing, town supplies, and mill power," was read by Mr J. T. Thomson, at the meeting of the Institute held on the 21st ult. : —

I claim for my present little contrivance some indulgence from the members of thU Society while I endeavour to explain iti properties and probable uses. By wy of pekoe, I m»y B&y tltft in my w

port tb Government, dated 12th August, 1867, 1 find T wrote as follows : —

" Large sluicing operations would appear to be the ultimate great industry of the interior (of Otago), and that the mining portion of the population have been fctfly alive to this will be proved by the enumeration in those, reports of their great and numerous water-races.

" The principle sources of water are in the Snowy Ranges, and others, the Dunstan, Umbrella, Nevis, Richardson, Pisa, Hawkdun, Kakanui, Eock and Pillar, Lammermoor, &a, &c. But it appears to me that in the Golden Stream — that ia, in the Clutha itself — iB to be found a power that will serve to wash away all itß auriferous banks, and clear the same to the profit of the miner. The fall of this river, from the lakes to the sea, is about 1000 feet in 100 to 120 miles, and the area from which It collects its waters above the gorge of the Dunstan iB equal to 3,325,000 acres. From these data, we can have a rude or comparative estimate of the power contained in it. Allowing 24 inches of fall over the area by averaging the greater fall in the mountains with the lighter fall in the plainß, we have 289,674,000,000 cubic feet per annum as the discharge of the Ciutha at the above point. This is equal to a discharge of 551,130 cubic feet per minute, but allowing, again, half the rainfall to be absorbed by evaporation, the actiial result will be 275,565 cubic feet per minute.

"How to arrive at the object of the enquiry. We have the fall from the lakes to the sea, as above stated, at 1000 feet, which gives 422,500 nominal horse power. This may truly be said to be a very valuable property of the province, which always remains to it, and which, if only partially made use of, may be fraught with great importance to the prosperity of our interior population.

'•' It would not be consistent with the object of this report for me to suggest modes for the economical use of this power; but I may shortly state that I am aware that the mining population have applied it to a limited extent to social purposes. Of all contrivances, however, the simplest, I have no doubt, will prove the most successful, and the merits of the paddle wheel and the marine screw as motive powers will no doubt eventually be much canvassed. I would presumably advocate the latter, on account of its greater hold on the body of the flowing stream, its ready management and applicability in swift or slow currents, and its easy connection with, the apparatus for raising water."

Since the above report was written, of which this is a short extract, though, fully alive co the importance of the subject, I have, owing to constant engagements in other works and services, been able only to give an occasional thought in its direction. Since then I have heard of various attempts by miners and others to apply the force of the current of the Clutha to machinery employed in these enterprises, but how far successful they have been I have had no opportunity of learning. Some years ago 1 inspected two machines, one of which was for the purpose of raising water, and the other for working the gearing of a dredge, and in both oases the principle adopted wan that of the paddle wheel, though, one was of unusual construction, being set obliquely to the stream. Neither machine had great power, and having become disused, appear not to have met the expectations r of their designers. The paddle wheel, of proper and peculiar form, is no doubt well adapted for driving the machinery of floating mills (flour, bone, saw, &c.) in shallow rivers, where shallowneas of the stream would prevent the screw being applicable, and where there was large floatage capacity, at any rate, required to support the mill and its contents ; but its great size, cost, and weight of the paddle form of wheel create a most important objection to its general use in the Clutha, where only the temporary works of gold mining for the most part are engaged in. On the contrary, the great depth of the stream is particularly applicable to the screw, working as it does so much below the surface, and when jte smallness and lightness make it so easily handled, and its cheapness and simplicity render it of easy construction and repair.

The floating paddle wheel in a seven mile current requires 40 Bquare feet of floatboard to give a power of 12 horses, and of float boards there requires to be eleven in number ; while one screw of eight feet diameter would give the same Eower, and this, instead of requiring to c floated like the paddle wheel high out of the water by sufficiently strong barges or punts, can be immersed and attached not only to barges and punts, but to a buoy, rriiQ rope, boom, bridge pier, piles, or othtr fixtures suitable to the various situations.

The Otago sluice head, by the Goldfields Regulations, being equal to 95 cubic feet of water delivered per minute, naftohiti— of the abort dimension* will rai»e one iluict head to on elav&tioa of 70

feet, or 7 heads 10 feet, and this without intermission day and night. The advantage of the screw when made of timber (as I would support) is in its easy construction and repair — this fact should be particularly noted ; besides, the screw is the only portion of the apparatus, whether for mills or pumping gear, that need be, subject to accidents from floods. Acoidents from floods can also be avoided by drawing the screw into the banks till the danger from drifts ia over. On the Clutha, with its great body of water, the construction of the screw need not now be scientifically correct, but may be of the rudest description, the fault in form being amply compensated for by the superabundance of power. Thuß, the screw may be easily made by a common carpenter and blacksmith — in fact, out of an old gin case and a piece of scantling I would engage to make a very effective 2 horse- power machine. The contrivance then, I am sanguine in stating, supplies that which is wanted by the sluicing, dredging, pumping, and other enterprises on the banks of the Clutha, viz. — an inexpensive and simple machine for economising the power of the current. The nature of the contrivance is simple. A model is now on the table for inspection. I will be happy to show it at work in tha stream of the Water of Leith, at anytime the members of this Sooiety may appoint, when they could judge of its effectiveness themselves.

The model will be seen to be made of wood, in the make- shift fashion much had recourse to on the diggings, the only portion of it executed by skilled labour being the brass force-pump and india-rub-ber tubing. The screw (or more properly speaking fan wheel, as the blades in this little example are plain and not to the helical curve) is 15 inches in diameter. The blades are set to an angle of 20 degrees to the disc, and in a two-mile current the revolutions are once per second nearly. The pistons of the pump are worked by a crank, and, being singleacting, propel its contents once per second. The diameter of the oylinder is three-quarters of an Jnoh, and stroke of piston 2 7- 10 th inches. The quantity of water per stroke is therefore 11925 cubic inch. At the above rate of Bpeed, the quantity delivered therefore is 71 65 cubic inch per minute, or 59 "5 cubic feet, equal to 368 9 gallons per diem of 24 bours. This little model would, therefore, liberally supply the wants of a house of the largest class, and the first cost (not including piping) would .not be over 14 or L 5 sterling. -

For town supply, the screw, pump, and gearing would require to be designed for the population ; but taking for example one of the largest force pumps in the works of Messrs Burt, of this city, I fini it to be 4 inches in diameter, 8 inch stroke, single action once per second. TMb pump in constant operation would deliver 3 5 cubic feet per minute, or 5025 cubic feet, equal to 31,155 gallons for 24 hours, which would amply suffice for the supply of a town of 1000 inhabitants. Had the water supply to be raised 100 feet above the level of the river, such as would be necessary for Balclutha, Alexandra, Clyde, or Cromwell, as one-horse power raises 5*28 cubic feet to that elevation per minute, this power, allowing amply foi? friction, would suffice for the above ser* vice. So, were a screw applied to the pump revolving in a current of 7 miles per hour, one of 3 feet 6 inches in diarae* ter would do the duty.

The cost of the apparatus complete, deliverine; water at the top of the bank (not including street pipes, &c.) will o£ course vary with the nature of the posisition and relative facilities afforded* Where the river is narrow, the Borew and pump would best be held by a wire cable stretched across the current or arm of the rive. Where the banks are steep and rocky, a boom secured by stays and guys would be the best mode. Where the river is wide, a small punt, or even a barrel or buoy, might be used, and so forth. Ia either case the cost would not vary very much, so, taking the first by way of example, the following is an approximate estimate :—: —

In this case, for the avoidance of damage by heavy floods, arrangements would be made to elevate the wire cable and ' draw the screw and pump in shore till they had abated. I have already given the dimension* of a screw required to raise one sluice bead (95 cubic feet per minute) 70 feet above the level of the river, and an approximate estimate of the coat of the tame would b» a» follow*. The duty required would take * pingl© sating pump }4 Inohe?

diameter and 18 inohes stroke per second, or doable acting, 11 inches diameter and 14.5 inches stroke of same velocity :—: —

Of course the cost would be much modified by position and the relative facilities given by the state of the river, its banks, rocks, and currents. In applying the large machinery, it would be advisable to choose such sites as would afford rock foundations for the pump and gearings, so as to avoid the necessity of supporting the same by cable or punt, and in such cases the permanent material (cast iron) might be used solely for the piping.

As the altitude of water to be raised in many parts,' especially below theTeviot, does not require to be so great, of course much reduction in cost could alao be efieoted. This remark is ako partioularly applicable to the service of pumping water from river bank claims carried on below the level of the stream surface, where the height to be raised k generally small. In many parts of the goldfielda of Otago large capital has been expended in bringing water to claims on the banks of the Clutha now worked out. The coat of bringing in water when not available for other claims thus remains a loss. Thus a great advantage k gained under such circnmstances by the introduction of the contrivance and machinery proposed, inasmuch as the plant can be removed to other localities, and re-erected for new operations.

>0 fathoms of 3-moh galvanwed £ «. d. iron wire rope 8 15 0 ?ump 10 0 0 Sorew 10 0 0 150 feet of 2-inob. Indiarnbber tnbing at 2a 6d per foot ... 18 15 0 150 do do iron piping, at Is 3d perfeot t . 9 7 8 Carriage and labour of erecting... 60 0 0 £106 17 8

£ s. d. ?twnp 65 0 0 Jorew 20 0 0 iO fathoms of 4} inoh galvanised iron wire 46 0 0 50 feet of leather 8 inoh hose, at 5s per foot 37 10 0 .50 feet of oast iron 6 inoh pipes, at 4a per foot 30 0 0 Carriage and labour (cay) ... 100 0 0 297 10 0