As a means of readily detecting the presence of minerals in their ores the blow-pipe, in the hands of a skillful operator, is unrivaled. Nor is this skill at all hard to come by; two or three weeks' patient study under a good master should teach a great deal, and subsequently proficiency would come by practice in the field. Unfortunately, some very clever men have become so enthusiastic as to blow-pipe work that they have devised methods by which the amount of metal in an ore as well as its nature may be determined, but in so doing have so enlarged the amount of apparatus, and complicated the tests so seriously that the simplicity of the blow-pipe outfit is in danger of being lost, and its chief advantage of being forgotten; for there are many better ways of determining the value of an ore. A good assay or, better still, a mill run, is worth incomparably more than any quantitative blow-pipe test, even when conducted by a Plattner. The chemical blow-pipe is made of brass or German silver, with platinum tip. The best fuel, taking everything into consideration, is a paraffin candle in cold climates, and a stearine candle in hot ones. Tallow may do in an emergency, but it requires too much snuffing. [Illustration: REDUCING FLAME.] The blow-pipe can produce two flames. The one known as the reducing flame, and generally printed as R.F.; and the oxidizing flame, represented by the initials O.F. In the first the substance under examination is heated out of contact with the air and parts with its oxygen. In the second, it is heated in the air and absorbs oxygen. [Illustration: OXIDIZING FLAME.] Well-burnt pine or willow charcoal in slabs 3 inches by 1-3/4 inches is the material upon which the mineral to be tested is placed. A small shallow depression is scraped out of one side of it and the assay placed therein. Platinum wire, some 3 inches long, conveniently fused into a piece of glass tube as a handle, is used to test the coloration of minerals in the flame. This should be cleaned occasionally in dilute sulphuric acid and then washed in water. A small pair of forceps with platinum points serve a great variety of purposes, but the beginner must be careful not to heat metallic substances in them to a red heat, as he may thereby cause an alloy of the metal with the platinum and spoil them for future use. [Illustration: AGATE MORTAR.] Glass tubing one-twelfth to one-quarter inch in diameter and from four to six inches in length is used for a variety of purposes. From this material what are known as closed tubes may be made by heating a piece of the tubing at or about its center over a spirit lamp, and, when the glass has fused, pulling it apart. These closed tubes are used in heating substances out of contact with the air. A small agate mortar is indispensable. It must be used for grinding substances softer than itself to a powder, but it will break if rapped sharply.