Page:The American Cyclopædia (1879) Volume II.djvu/767

 BLOWPIPE 747 of air to mines. Two cylindrical-shaped ves- sels, such as long casks, are selected, of such sizes that one, when inverted, may easily move up and down within the other. The outer one is nearly filled with water, and is furnished with an air pipe, which leads from its upper part through the water, and through its bottom down into the mine. Upon the upper end of this pipe is a valve opening downward. The inner inverted cask surrounds this pipe. It has upon its upper end a large valve opening within. Being suspended by a chain to the end of a lever beam, or to the arm of a bob, air passes within as it is lifted up, and is pro- pelled as it descends through the pipe. By this alternating motion a continual current of air is supplied with little cost of power or at- tention. A more perfect arrangement of this machine is in making it double, by attaching one to each end of the lever beam. For blow- ing furnaces these machines have the common disadvantage of all water blasts, that they cause the air to take up more or less moisture, which is discharged into the furnace, and must to some extent diminish the effect of the blast. BLOWPIPE, in the simplest form, a small metallic tube of tapering shape, its smaller end curved around to form a right angle, and the larger end of convenient size for applying to the mouth, designed to concentrate the heat of a flame upon a particular point. It is 8 or 10 inches in length, with a bore varying from j^ to -fa of an inch, but drawn out at the small extremity to a very minute aperture. Through this air is blown upon the flame of a lamp, causing a portion of the flame to be diverted in a jet of intense heat. It is an instrument of great use with jewellers for soldering small pieces of work, and with glassblowers and enamellers, for softening and working small articles. By these it is often used upon a larger scale with a bellows for supplying it with air, instead of furnishing this by the month. But the most important use of the blowpipe is to the mineralogist and analytical chemist, in whose hands it is made to serve the purpose of a small furnace, with the ad- vantage that the operations taking place are directly under the eye. When used, the point is placed in the flame of a lamp, and the cur- rent of air is directed across this, by a steady blast from the mouth. A lateral cone of flame is thus produced, which is pale blue without and blue within. At the point of the inner blue cone is the greatest intensity of heat. A small particle of metallic ore placed upon char- coal, and kept at this point, may be reduced to a metallic state, the charcoal aiding the process by its chemical action in abstract- ing the oxygen of the ore. If of difficult re- duction, the experiment may be aided by the introduction of proper fluxes, as in crucible operations. The outer cone of flame in con- tact with the air possesses oxidating proper- ties ; and in this the preparatory operation of calcining and desulphurizing is effected upon the particle of ore, before it is submitted to the reducing flame. Control is thus had over any desired amount of heat, and with a facility of employing it for different purposes in a small way, which renders the blowpipe far prefer- able for experimental purposes to the cumber- some furnaces and other expensive apparatus which were required before its application for determining the properties of mineral sub- stances. The process of cupellation is very readily effected upon small pieces of metallic lead containing silver or gold. The button of metal is placed in a small cupel of bone ash, and this is laid upon a piece of charcoal for a support. It is thoroughly heated and the button melted in the reducing flame, and then exposed to the action of the oxidizing flame. In this the lead is kept in fusion, and a pellicle of oxide of lead is continually formed upon the surface, and as constantly absorbed in the cupel, till the lead is all thus removed, and the little globule of the more precious metal, so small perhaps as to be scarcely visible, is kept as a bright point in the centre of the cupel. By working upon a weighed quantity in re- peated operations, and adding the products to each other, the analysis may be made quanti- tative by the use of the ingeniously contrived apparatus applied by Plattner to the estimation of the weight of minute bodies. Another im- portant use of the instrument is melting small particles of undetermined substances with differ- ent fluxes, as borax or salt of phosphorus, upon a fine piece of platinum wire, hooked at the end to sustain the little bead. By the reaction of the ingredients of the substance with the flux, as seen in the mode of melting, the color of the head in one flame, and its change to an- other color in the other flame, these ingredients are detected and the compound determined. For example, copper gives a green bead in the outer flame, but a red one in the inner when borax is the flux used ; iron gives a yellowish green bead, cobalt a blue bead, and manganese a violet bead, which is made colorless in the in- ner flame. The qualitative analysis is rendered more complete by subjecting the substance to the action of the blowpipe in glass tubes, for the purpose of detecting the volatile ingredients, as water by the steam, ammonia by its vapor and odor, sulphur by its odor and yellow sublimate, and arsenic by the metallic ring it forms around the inside of the tube, where its vapor con- denses. This may be satisfactorily effected where the particle under examination is too small to he visible without the aid of the microscope. The substance may also be dis- solved in acids in glass tubes, and the precipi- tates obtained, freed from some of their asso- ciated matters, be subjected to the test by the blowpipe. Many minerals may be determined by simply heating them alone in platinum- pointed forceps and observing whether they fuse and how ; what color they impart to flame, and what appearance the fused mineral pre- sents. Thus the blowpipe, with a few simple