SEARCHING FOR IRON.--Any heavy mineral of a black, brown, red or yellow color may be suspected to be iron. To prove it, dissolve some in oil of vitriol and pour in an infusion of nut-gall or oak-bark; if it turns black, iron is present. If a ton of rich magnetic ore costs more than $4 at the furnace, good hematite more than $3, and poor ores more than $1.50 or $2, they are too expensive to pay, unless iron is unusually high. Deep mining for iron is not profitable. Generally speaking, a bed of good iron ore, a foot thick, will repay the cost of stripping it of soil, etc., twelve feet thick. Red and yellow earths, called ochres, contain iron. Magnetic ore is easily found by a compass. CHAPTER V. ASSAY OF ORES. WHEN AN ORE WILL PAY--WASHING FOR GOLD AND PLATINUM--HOW TO ASSAY GOLD IN THE SIMPLEST WAY--TO TEST ANY ROCK FOR GOLD AND SILVER--TO FIND THE PURITY OF GOLD--TO DETECT AND ASSAY SILVER ORES--ASSAY OF COPPER, IRON, ZINC, TIN AND LEAD ORES--READY METHOD OF TESTING GRAPHITE. One of the first questions asked after the discovery of a metallic ore, is--“will it pay?” We propose to state in plain words a method of determining the character and value of the principal ores, so that any intelligent man, however unscientific, may answer his own question. The chemical analysis or exact assaying of ores is too complicated, and must be left to professional assayers. “Will it pay?” is an important query; for many ores of even precious metals, are not “paying.” Whether an ore is profitable depends not so much upon the relative value of the metal as upon the ease of separating it from the rock or “gangue” as it is called. Thus the minimum percentage of metal, below which the working of the ore ceases to be profitable is-- Of Iron, 25 per cent. Zinc, 20 “ Lead, 20 “ Antimony, 20 “ Copper, 02 “ Tin, 01½ “ Quicksilver, 01 “ Silver, 1/2000 “ Platinum, 1/10000 “ Gold, 1/100000 “ That is, an ore of iron which contains less than 25 per cent. of metal will not pay for working; for the reduction of iron in comparison with copper ore is very difficult. Gold is very easily extracted, and hence some quartz rocks which do not apparently contain a particle of gold, pay well, a bushel of rock often yielding half an ounce. Iron occurs in large masses or beds; but the other metals are scattered in fragments through sand or soil, or exist in veins running through rocks.