In the stamp-house and auxiliary washing-house the labyrinths are used for settling the slimes from the turbid water of the sand jigs. They are of the usual Hartz type, and consist of series of long deep boxes built side by side, and communicating at each end by cuts in the side wall. There are eight of them in the stamp-house of eleven boxes each, and six of them in the auxiliary washing-house of twelve boxes each. The circulation in each set is 25"-30" in length. ECONOMICAL RESULTS OF THE DRESSING. In conclusion, we will consider the practical results that have been attained from the dressing of ores in these works. Since they were started careful detailed accounts are said to have been kept of the various dressing operations, and of the working of the various machines. These accounts show the amounts fed to, and discharged from each operation, with careful analyses of the products. Figures from these accounts will probably find publication from time to time in the pages of the Zeitschrift für Berg-Hütten-und Salinen Wesen, which is the government organ, and in which, in addition to the careful paper of Mr. Kutscher, the engineer of the works, various data as to experiments and changes in the works have already appeared. As continuous, systematic, careful accounts have never been kept of the operations of ore-dressing on so large a scale, if at all, except for experiments, the most valuable results may be expected from them. One very practical result will be the basis they will afford for careful and frequent comparative experiments, and the great addition they will make to the accurate figures concerning ore-dressing. It does not seem a very wild prediction to anticipate as a not distant result of the accumulation of such figures the radical alteration of the whole method of treating sands and slimes in this establishment. The only exact figures thus far published for these works are for five months in the year 1875. During that period 18,300 cubic meters of ore were treated, which were accounted for by the following products: This showed, therefore, for five months, a total dressing loss of 759 cubic meters, or 4.14 per cent. of ore which passed off unaccounted for. It was probably lost in two ways: (1) some of it went off still suspended in the water leaving the works. If we suppose 15 cubic meters of water leaving the works per minute, this would give about of a pound of material suspended in every cubic meter of water leaving the works for five months. Part of it, however, was (2) in the ore thrown away in hand-picking, and contained in the tailings from the jigging houses. The average of many analyses made show the following percentage of galena to be contained in the barren material sent to the dumping-ground, and in the slimes going off suspended in the waste water or thrown away: To even partially recover that contained in the first class coming from hand-picking and jigging would necessitate further reduction by rolls or stamps for the respective classes, and further handling by jigs, buddles, tables, etc. It is very properly considered that the expense of recovering it would exceed its value. It seems probable that the figure for the second class of loss might be materially reduced by laying down more perfect apparatus than their present buddles and tables. The figure for the third class they expect to reduce by increasing the number of slime and clearing pits, and have probably done so already. From these analyses they reckon the absolute dressing loss in galena during 5 months at 4083 centners (204 tons), which they distribute as follows: 1. Dumped material from hand-picking and jigging, 2. Tailings from buddles and tables, 3. Slime suspended in waste water, . But they obtained 43,552 centners (2122) tons of the galena in the ore in a concentrated form. The dressing loss, therefore, referred to galena in the ore alone, was equal to 9.375 per cent., or, as before stated, 4.14 per cent., if referred to the total ore. They profess to be very well satisfied with this result, and may well be so, for their figures show close work. They propose, however, to better these figures, and the amount of galena contained in the tailings from their buddles and tables point clearly to a very necessary change of method and apparatus. JET PUMPS FOR CHEMICAL AND PHYSICAL LABORATORIES. BY ROBERT H. RICHARDS, PROFESSOR OF MINING, MASSACHUSETTS INSTITUTE OF TECHNOLOGY, BOSTON. (Read at the Amenia Meeting, October, 1877.) DURING the winter of 1868-9, I was called upon by Professor F. H. Storer, to put up the Bunsen filter pump in the chemical laboratory of the Masschusetts Institute of Technology. As the laboratory is on the lower floor, it was found necessary to use a great deal of cumbrous pipe and apparatus to get the necessary column. It was then suggested that if an instrument could be devised which would make use of the hydrant pressure in the service-pipe, it would do away with the objectionable features of the Bunsen pump. After using the Bunsen pump for some years, the jet pump to be described in this paper was devised, and it has since been adopted by Prof. Wing in the quantitative laboratory of the school. I am much indebted to Prof. Wing for his aid in starting the manufacture in brass of these jet pumps, whieh are now to be had in Boston. The jet pump much resembles the Giffard injector in form. It differs from it in the fact that water is the impelling fluid, and air the impelled, while with the injector steam is used to impel water. The principle of condensation of steam, which is availed of in the injector, is entirely wanting in the jet pump. Air Water 20 Foam The jet pump consists in a water jet, w, (see figure), a constriction or waist, a, and a waste tube, o. The success of the jet pump depends on the following conditions: 1. The relation between the sizes of sectional area of a and w. 2. The proximity of a and w. 3. The form and angle of the two hollow cones whose vertices make the constriction a. 4. The relative size of sectional area of w and o. 5. The zigzags, or an equivalent means of making foam. In the following discussion, let a, w, and o represent the diameters of these parts of the jet pump. A number of experiments were tried to ascertain what was the best relation between w and o, from which it was decided that when a good foam was produced in o, but if the proportions were much increased, the foam ceased to fill the bore of the tube, and the pump ceased to work. The zigzag bends or some equivalent means of lashing the waterjet into foam, are needed to start the operation of the pump, for without them, the water-jet would come through a and o, intact as a cylinder of water, and would escape at the outlet without doing any work, but by breaking the jet into foam, a partial exhaustion is at once made in the vacuandum, which causes the foam to rush back to a, and as soon as this is accomplished, the jet pump begins to operate in good earnest, and the issue between the water and air takes place, as it should do at a. The angle of the cones was determined by running a jet of water into a beaker of water, the jet being held just above the surface of the water, the diverging angle of the foam resulting was carefully measured, and was found to be from 14° to 17°, and not to vary with the pressure of the water in the jet. Accordingly, the waist is now made of two cones, with an angle of 17° each. As to the proximity of a and w in small jet-pumps, about 4 inch was found best, but while it was not found that any one distance was better than all others, it was clearly demonstrated that this distance should not be too great, else the water-jet will lose its identity before it gets to a, and the pump will fail to work. To determine the relative sizes of w and a, that would do the best work, a large number of careful experiments were tried, with different ratios, of a2: w2, and with different pressures of water, and from these experiments, the conclusion was reached, that to make the best average jet pump to do average work with average water pressures, the ratio between the two should be Accordingly, the jet pumps now made in Boston, are of this proportion. The jet pump may be used either as an air pump for exhaust, or as a blower. When used as an exhaust, it is simply screwed to the hydrant, and the vacuandum is attached to the side tube, where the air enters by rubber tube. The jet pump may be used very well to aerate fresh water aquaria |