_Action of Heat_.--This is, perhaps, the most important characteristic, and, when taken with the preceding data, will identify any of the minerals found in any one locality, which I will describe, from each other. The heat is applied to the mineral by means of a candle and blowpipe. A thick wax candle answers well, and an ordinary japanned tin blowpipe, costing twenty cents, will serve the purpose. The substance to be examined is held on a loop of platinum wire about one inch to the left and just below the top of the wick, which is bent toward it. Here it is steadily held, as is shown in Fig. 1, and the flame of the candle bent over upon it, and the heat intensified by blowing a steady and strong current of air across it by means of the blowpipe held in the mouth and supported by the right hand, whose elbow is resting upon the table. The current of air is difficult to keep up by one unaccustomed to the blowpipe, the skill of using which is readily obtained; it consists in breathing through the nostrils, while the air is forced out by pressure on the air held by the inflated cheeks, and not from the lungs. This can be practiced while not using the blow-pipe, and may readily be accomplished by one's keeping his cheeks distended with air and breathing at the same time. This heat is steadily applied until the splinter of mineral has been kept at a high red heat for a sufficient length of time to convince one of what it may do, as fuse or not, or on the edges. The first two are evident, as when it fuses it runs into a globule; the last, by inspecting it before and after the heating with a magnifying glass; sometimes it froths up when heated, and is then said to "intumesce;" or, if it flies to fragments, "decrepitates." Upon the first it is further heated; but in the latter case, a new splinter of mineral must be broken off from the mass and heated upon the wire very cautiously until quite hot, when it may then be readily heated further without fear of loss. For holding the splinter of mineral, which should well represent the mass and be quite small, is a three-inch length of platinum wire of the thickness of a cambric-needle; this may be bought for about ten cents at the apparatus shop. The ends should be looped, as is shown in Fig. 2, and the mineral placed in the loop.