In former times mining was entirely carried on by primitive methods with hand labour, but the utilization of dredges has steadily increased, since their introduction in 1900. In 1909, 13 per cent. of the total production was obtained by dredging, and in 1914 this percentage rose to one-third of the total output. The season during which dredges may be employed extends on the average from the middle of April to the middle of October. In the South Verkhotur and Perm areas dredges have been used in the large enterprises; but at the small mines the working is very primitive, and carried on largely with the help of _starateli_, or tributers. In 1914 a modern 7½ c. ft. dredge was installed on the Nikolaie-Pavdinsk Estate. In mines where dredging is not in use, the gravels are mined by open cuts, or, if the overburden is thick, shafts are employed. The former method is much preferred, both on account of its relative cheapness, and also because it is possible to obtain a better clean-up of the bedrock. The usual types of stationary plant in use include the _botchka_, or conical revolving screen; the _tchaska_, or puddling machine, with a bottom of perforated iron plates; and the _boronka_, or conical screen, on which the stones and clay are turned over by a double rake[55]. The gold is removed by amalgamation with mercury in wood, iron or porcelain bowls. Special methods are in use in certain parts of Russia for working the deposits during the winter. The workings are allowed to freeze, and the frozen ground is mined after being partially thawed by means of wood fires. The method is simple, but care must be taken to ensure that the thawing does not proceed too far, otherwise the ground collapses, and the workings become flooded. The method is suitable for depths to 30 ft., and in localities where the snowfall is comparatively slight. Latest reports from Russia indicate that no dredges are now working there, the platinum being produced by hand methods only. Some interesting experiments were recently carried out by V. N. Chorzhevski in the Nizhni-Tagilsk district, with a view to testing the commercial possibility of mining platinum _in situ_. The metal here occurs, in association with chrome iron ore, in dunite rock, which in this region extends over an area of 11½ sq. miles. The platinum appears to be present in quantities directly proportional to the amount of chromite in the rock. The dunite is first ground under runners; the chromite slack is separated from it; and after this has undergone a second grinding, the metal is separated by washing[56]. An experimental test, carried out in March 1917, is stated to have produced over 200 oz. platinum from 9,720 lb. chromite slack. Another experiment with 3,600 lb. of grey slack, “or fines,” consisting chiefly of undecomposed dunite obtained from the dredges, is reported to have yielded ⅓ oz. of platinum.