GOLD MACHINERY.—We have just received a letter from J. W. Cochrane, of this city, the inventor of the gold quartz crusher which was illustrated on page 364, Vol. 7, Scientific American, who is now in London with one of his machines grinding gold quartz shipped from California. He is convincing the most skeptical that he can take gold quartz in lumps of 30 cubic inches, and with the aid of two men he can pulverize and amalgamate no less than forty tons of it per day. The whole expenses for labor and steam power does not cost over one shilling sterling per ton. He challenges any other machine lor 125,000 to equal it. He is receiving orders for Australia, California, England, and Spain. He believes that Buffum's Amalgamator, which was also illustrated in our last volume, to be without a superior. He asserts that the quartz and mercury should never be ground together; and the reason he gives for entertaining this opinion is, that in grinding the mercury is finely subdivided, mixed witft the sand, washed away in the water and lost. The grinding acd amalgamating, he asserts, should be performed by separate machines, entirely different in their nature and action. Water Tanks of Locomotives—On page 348, this Volume of the " Scientific American," we noticed an improvement in the construction of locomotive water tanks, invented by A. W. L, Rivers, of Charleston, S. C. The " New York Railroad Journal " noticed the improvement, and said it was not new—that it had been tried on the New York and Erie Railroad, and it was lound to pessess no advantage. We have received a letter from Mr. Rivers on the subject, and in it he says, " his tank has been successfully tried, and is now used on the South Carolina Railroad, and the Superintendent, N. Darrell, Esq., a man of experience and ability, wishes that all the tenders on the road were builton the same plan." He is positive that the water tanks of the tenders on the Erie Railroad, were differently constructed from his.