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Some light may be thrown upon the question by experience in other places, and in this connection we find the following statements in Mr. T. A. Rickard's " Stamp-milling of Gold-ores," pages 125, 126, the first reference being to Australian practice: "At the Britannia United, on Bakery Hill, in Ballarat, the water used in the batteries is warm, and is made so by conducting the condenser water of the engine into the tank which supplies the mill. Two points open to discussion are here suggested, the use of warm water and the addition of lime. The object of heating the battery water in such a warm climate as that of Ballarat does not appear very evident. The use of condenser water in any mill is decidedly objectionable. To consider these two propositions, let us take first the effects of warm water upon amalgamation. At the alluvial mines of the mountains of the interior of Otago, New Zealand, the use of mercury, the good friend of the miner all the world over, is hardly known, and the explanation given is that mercury will not act in the cold climate of that region. This is due to the use of hot water in cleaning up at both mines and mills. The idea is, of course, quite an erroneous one, though there is a substratum of truth in it, from the fact that amalgamation is usually assisted by heat and retarded by cold, but within narrow limits only. The amalgamation of gold, not silver, in ordinary stamp-milling, not pans, is here discussed. Ou the other hand, at Black Hawk, at over 8,000 ft. above the sea-level, in the bitter cold of the Colorado winters, the mill-men will tell you that cold weather is better for amalgamation upon the plates than summer heat. Why ? Because heat thins the amalgam, and the vibration of the mill, due to the falling stamps, causes the globules of mercury to run off and down the surface of the amalgainatiug-tabies, while cold (which thickens the amalgam) tends to keep it in position. From one point of view hot water is to be recommended. Slimes which will float on cold water will sink in warm water, owing to the expansion of the air bubbles, which float the fine dust and are the raison d'etre of the slimes. On the whole, however, while amalgamation (and here the amalgamation of gold is the only question discussed) is assisted by heat, yet below the temperature of boiling water the effects of a small rise are so slight that it is doubtful if the use of warm water is to be advised in ordinary gold stamp-milling. It is certainly not to be recommended in summer at a locality having the climate of Ballarat, and therefore its use at the Britannia United is to be objected to. (At the time referred to it was summer, and the temperature outside the mill 82 deg. Fahr.)" The excellent paper on the " Amalgamation of Free-milling Gold-ores," by Mr. Louis Janin, jun., in "The Mineral Industry," vol. iii., has brief references only to this question. Thus he says, on pages 328 and 343 : " Some mill-men believe in heating the battery water, but it would seem doubtful if this can produce any result other than to create a fluid amalgam. The plates in particular are softer when warm water is used, but this is a doubtful advantage. If the water be heated at all it should not be done by the direct application of the exhaust steam, as is explained elsewhere. A peculiarity of amalgam is that it contains more gold in winter than in summer. This is due undoubtedly to the warmer water in summer making the amalgam more fluid. The difference ordinarily is slight. Amalgam that retorts 40 per cent, in summer may retort 45 per cent, in winter." The experience reported by Mr. Allan J. Clark in the Homestake Mill itself points rather to the theory that the effect is chiefly mechanical. In the cases reported by him the amalgam from the third row of plates is softer than that of the first row —it rarely retorts over 20 to 22 per cent., as against 35 to 37 per cent., and after standing for some time after squeezing it assumes a more or less liquid condition—the material collected during two weeks after coming down to the assayoffice for retorting, fully 75 per cent, in liquid form, with a few pasty lumps included in it. Moreover, this condition has not been so noticeable during the winter months as it was during the summer and autumn. In this case the colder water, by hardening or stiffening the amalgam, may prevent scouring, and so give higher results. Mr. Reed, amalgamator at the Golden Star Mill, experimented with a battery that had been worked for some time on water at 56 deg. Fahr. Before leaving the mill one evening he changed it to 70 deg. Fahr.—at this time the plates being covered with amalgam —and next morning at 7 o'clock much of this had washed off, small wedges remaining where the brushes had broken the even surface of the amalgam ;at 11 a.m. these had disappeared, and the plate was almost bare. This was a silver plate; the copper-plate of the first row showed no such changes in working when the temperature is varied. Mr. Reed adds that he has only occasionally observed any evidences of chemical action when using warmer water, a black scum showing on the surface of the plate when it is gently rubbed with the hand. So far, therefore, the weight of testimony seems to be rather in favour of the mechanical effect. The experience of mill-men in other localities may point to different theories, however ; it would at any rate be of value. Mr. Grier's discovery is suggestive, and it is quite possible that it might be of advantage to pay more attention to the temperature of the water than has heretofore been done in many places.

PATENT RIGHTS GRANTED. An Improved Process for extracting Gold from Ores, Minerals, and other Gold-bearing Substances. We, James Gow Black, of Dunedin, in the Colony of New Zealand, Professor of Chemistry in the University of Otago, and Robert Challen Skeet, of Oamaru, in the Colony of New Zealand, do hereby declare the nature of our invention for " An improved Process for extracting Gold from Ores, Minerals, and other Gold-bearing Substances," and in what manner the same is to be performed, to be particularly described and ascertained in and by the following statement: —