214 REPORT — 1873. 



On the "Duti/" of Arrastres hi reducing Gold Ore in Italy. 

 By C. Le Neve Fostek, B.A., D.Sc., F.G.8. 



After defining " duty " as the percentage of the total gold contents extracted by 

 the machines, the author proceeded to give the results of experiments carried on 

 by him for three years (18UU-72) at the Piedimulera Reduction Works, situated at 

 the foot of the Val Anzasca, and belonging to the Pestarena Gold-Mining Company. 

 The machines used for reducing the ore are improved arrastres, on a plan invented 

 by Messrs. T. and J. Roberts and H. Iloskings. 



The ore for amalgamation, containing from 9 to 13 dwts. per ton, was very care- 

 fully sampled and assayed before it went to the arrastres. The average result for 

 the first year was, that the arrastres extracted 7?>'S per cent, of the gold in the ore, 

 in the second year 78-o per cent., and in the third year 82 per cent. The author 

 called attention to the ftvct that the average duty of the six winter months, when 

 the average temperature of the water supplied to the mills was 39'' F., was always 

 higher than the average duty of the six summer mouths, when the average tempe- 

 rature of the water supplied "to the mills was 52° F. He considered that the fall in 

 duty for the summer months was due to the water being charged with mud from 

 the glaciers, whereas in winter the water was quite clear. The fact, however, was 

 instanced to show that high duties are quite compatible with cold water. 



On the Irrigation of the Casule District, By P. Le Neve Foster, Jun. 



On the Mechanical Treatment of Fibrosis Substances. By S. C. Lister. 



On Na2yier's Pressure Log*. By James R. Napier, F.R.S. 



On Stone-dressing in Bradford. By ARcniBALD Neii.l. 



There is little machinery at work in the stone trade of the district ; for, although 

 stone-moulding and -dressing machines have been at work on Eath, Portland, and 

 other soft stones of the southern counties, they are not adapted to work the hard 

 stone of this district, the great grinding-power of the stone on the tools being a 

 considerable difhculty. We have the ordinary steam stone-saws, that are very 

 useful, enabling the builder to cut the stone in such a manner as always to secure 

 that when set in the building it shall be on its natural bed. At the same time 

 it is a great economizer of material, saving fully 10 per cent. Coulter and Harpin's 

 and the ordinary rubbing-tables are in use, and answer well for flags, landings, and 

 common work. Still we want machines that will perform the more expensive 

 portions of masons' work, such as moulding, sinking, and circular work. The 

 author exhibited sketches of four machines which he had constructed — two for 

 working stone, and two for wood. Though simple, they are yet capable of doing 

 a considerable amount of work. In No. 1 the stone is placed on a travelling table, 

 and carried against the cutters held on a revolving wheel. The stone is then cut 

 to a true face. The grind on the tool is considerable, but the expense in steel and 

 sharpening is not so much as in the ordinary masons' chisel. The work is done 

 at one third the cost of hand labour. No. 2 machine is for rubbing stone to a true 

 and smooth face. The stone is roughly punched to a shape and fixed on a table. 

 This table is moved before the face of a revolving plate, while weights draw the 

 stone up against the face of the plate. Sand and water are put on, and the work 

 is done at about one third the cost of hand labour. This machine is simple and 

 cheap, and requires little power to drive it. The author concluded by exhibiting 

 drawings of two machines for working wood. 



I 



* Published in cxtenso in the 'Engineer' for Oct. 3, 1873. 



