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 3/10 to 1/10 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 mouth. 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 advantage that the operations taking place are directly under the eye. When used, the point is placed in the flame of a lamp, and the current 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 charcoal, and kept at this point, may be reduced to a metallic state, the charcoal aiding the process by its chemical action in abstracting the oxygen of the ore. If of difficult reduction, the experiment may be aided by the introduction of proper fluxes, as in crucible operations. The outer cone of flame in contact with the air possesses oxidating properties; 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 preferable for experimental purposes to the cumbersome furnaces and other expensive apparatus which were required before its application for determining the properties of mineral substances. 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 repeated operations, and adding the products to each other, the analysis may be made quantitative by the use of the ingeniously contrived apparatus applied by Plattner to the estimation of the weight of minute bodies. Another important use of the instrument is melting small particles of undetermined substances with different 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 bead in one flame, and its change to another 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 inner 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 condenses. This may be satisfactorily effected where the particle under examination is too small to be visible without the aid of the microscope. The substance may also be dissolved in acids in glass tubes, and the precipitates obtained, freed from some of their associated 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 presents. Thus the blowpipe, with a few simple instruments and some tests, all of which may be easily transported, serves the purpose of a portable laboratory.
In skilful hands all mineral substances may be determined and a complete qualitative analysis made by it; and by the improvements introduced by Prof. Plattner, manv quantitative analyses maybe effected for practical purposes. - The blowpipe was first applied to the examination of minerals by Swab, counsellor of the college of mines in Sweden in 1738. Cronstedt, of the same country, next took up the subject, and made great use of the blowpipe for distinguishing minerals by their chemical properties. This was for his work on mineralogy, in which he introduced the classification of minerals according to their chemical composition. This book was first published in 1758, and was translated into English by Von Engestrom in 1765, who added to it a treatise upon the blowpipe, and the manner in which it was used by Cronstedt. The attention of scientific men was thus directed to its great use as an analytical instrument, but the difficulty of learning to apply it, without practical instruction, prevented its being so generally received as it deserves to be; and had not the Swedish chemists continued to employ and improve it, it might after all have fallen into disuse.
Bergman found it very serviceable in his chemical researches, and Gahn, who assisted him, carried its use to a higher state of perfection than had before been attained. Berzelius enjoyed the most friendly intercourse with this remarkable man, and preserved in his "Elements of Chemistry" the most important results of the experiments, which Gahn never took upon himself to publish. Speaking of Gahn in a later work ("Treatise upon the Use of the Blowpipe"), he remarks that when travelling he always carried this instrument, and all new substances which he met with he subjected to its test; and it was an interesting thing to see the readiness and certainty with which he ascertained the nature of substances not recognizable by their external properties. Long before the subject of vegetable substances containing copper was brought to public notice, Berzelius says he has often seen Gahn extract from the ashes of a quarter of a sheet of paper particles of metallic copper visible to the eye. The most perfect form of the instrument now in use is that adopted by Gahn. The long, straight tube which serves as the handle passes into one end of a cylinder three fourths of an inch long, and half an inch in diameter, from the side of which the jet tube projects about 1 1/2 inch to its capillary extremity.
The object of the cylinder is to intercept the moisture of the breath, which without such an arrangement passes through the tube, and is projected in drops into the flame. Berzelius added a little jet of platinum, which slips over the end of the brass jet, and which may be taken off and cleaned whenever it becomes obstructed, by burning out the impurities with the blowpipe itself. The aperture of the platinum jet is 0.012 to 0.015 inch in diameter. Several of them, with holes of different diameters, accompany the instrument, and are changed as the flame is desired to be more pointed and intense, or of less intensity and to cover a larger surface. Considerable practice is required to blow continuously without exhausting the lungs. This is done by breathing only through the nostrils, and using the cheeks for propelling the air. By this means a steady current may be kept up for a long time without fatigue. The process is with some persons very difficult of attainment, but is at last caught, one knows not how, and is never afterward lost. Quick's gas blowpipe, and automatic blowpipes worked by a small rubber ball held in the hand, have been introduced to save the fatigue of blowing from the lungs.
The treatise on the blowpipe by Berzelius, which long occupied the first rank among the works upon this subject, and was translated in this country by Mr. J. D. Whitney, has been superseded by an exhaustive book by Professors Plattner and Richter of the royal mining academy of Freiberg. Prof. Plattner has incorporated the results of his operations with the blowpipe in a work of great interest, which has been translated into English by Henry B. Cornwall of the Columbia college school of mines. This forms a very valuable manual, containing the descriptions of the various processes for estimating the quantities in which many of the metals are found in their natural and artificial compounds, as also for detecting the qualities of metallic combinations in general. The methods adopted by Prof. Plattner for separating the minute particles, and ascertaining their weights, are of great ingenuity and simplicity, and valuable for the promptitude with which they may be used; but to be successfully practised, they require long and patient use of the instruments. - The little globules of gold and silver extracted from their combinations by the blowpipe are often too small to be weighed, but their quantity is determined by a method introduced by Harkort of measuring their diameter.
This is done by running the globules along between two lines upon an ivory scale, which diverge at a very small angle, and are crossed by many other lines at equal distances from each other, which serve as the divisions of the scale. Wherever the globule is found to be contained between the two diverging lines, its diameter is at once obtained, and the weight corresponding to this, whether of gold or of silver, these having been previously determined with care for the scale. To insure exactness in the measurement, a good magnifying glass is required, and care to view the scale in a position perpendicular to the line of sight. The measuring instrument of Ri'iger, furnished with a micrometer screw, yields exceedingly accurate results, and saves the fatigue of the eye. Although the globules are not often perfectly spherical, it has been found in practice that within certain limits this method may be relied on for the approximate analysis of many metallic compounds. - The compound or oxyhydrogen blowpipe is an apparatus invented by Dr. Robert Hare of Philadelphia, in the early part of the present century.
By this a mixture of oxygen and hydrogen is made to produce the jet, which being inflamed just beyond their point of mixing, an amount of intense heat is evolved far exceeding what had ever been before obtained. Substances hitherto regarded as infusible were melted down with great facility. Pure lime was observed to give an intensity of light greater than had ever before been seen. This caused its use to be recommended by Lieut. Drummond of the British navy for lighthouses, and his name has since been applied to the light, which was first obtained and noticed by Dr. Hare. The first arrangement adopted by Dr. Hare was to collect each gas in a separate reservoir, and cause them to be discharged by separate jets at the point of combustion. But finding that a more intense heat is generated by first mixing them under some pressure, he brought them into a single tube, and caused this to terminate in 15 jet pipes of platinum. These were adjusted so as to pass through a vessel, in which ice or snow could be placed to keep the gases from becoming heated, and thus obviate the danger of explosion by a retrocession of the flame into the single pipe.
With an apparatus of this kind Dr. Hare succeeded in fusing large quantities of platinum, and at the meeting of the American philosophical society in January, 1839, he exhibited a specimen of the metal, weighing between 22 and 23 oz. troy weight, which was part of a mass of 25 oz. fused in May, 1838, about 2 oz. of the metal having flowed over in consequence of the cavity not being sufficiently capacious to contain it all. He also obtained platinum directly from the crude product of the mines. Dr. Hare observed that the most intense heat was generated when the proportion of the gases was the same as in water, viz., two volumes of hydrogen and one of oxygen, and that by the use of a condensing syringe for forcing the mixture with considerable pressure, the effect was still further increased. With this modification, Prof. Clarke, of the university of Cambridge, England, repeated the experiments made years previously by Dr. Hare. He also enclosed in the pipe leading from a vessel containing the two gases a great number of layers of fine wire gauze. Though his experiments were successful, and were a subject of great scientific interest, the apparatus proved too dangerous for use, the wire gauze not preventing the explosion of the gases.
Further improvements have been introduced by filling the safety chamber with alternate layers of wire gauze and of the finest fibres of asbestus. Brass wires are also used, packed closely together in a bundle and pressed into the cylindrical portion of the chamber. The quality of the oxygen is found to have a sensible effect upon the intensity of the heat, that obtained from chlorate of potash being much preferable to that from the oxide of manganese. Few substances are found capable of resisting the high temperatures obtained by this blowpipe. Platinum melts instantly, and gold in contact with borax is entirely volatilized. Quartz crystal melts with a beautiful light, pieces of china ware are fused and form crystals, and flints produce a transparent glass. - An apparatus of great efficiency and simplicity of construction was used in New York city by the Drs. Roberts, dentists, for remelting platinum scraps, and converting them into mer-chantable plate. They employed two copper gasometers of cylindrical form, one for each gas, that for hydrogen of the capacity of 220 gallons, and that for oxygen of 80 gallons. The pressure of the Croton water, which is about 60 lbs. to the square inch, forced the gases through metallic pipes to the apparatus connected with the burner.
In this apparatus each pipe connects with a short brass tube, which is closely packed with wire, and these unite in another brass tube, which is also closely packed in the same way. From this, by a pipe of only about a quarter of an inch diameter, the mixed gases are then conveyed to the burner. This is a small platinum box inserted in a lump of plaster of Paris and asbestus, the apertures in the disk making its extremity being 21 little holes in three rows, such as might be made by the point of a pin. The platinum disk in which these holes are perforated is only about 1/2 by 1/4 inch in size. It is found that copper answers the purpose quite as well as platinum. The lump of plaster is constructed like the water tuyere of a forge or furnace, and is kept cool by a current of cold water constantly flowing through it. The supply of the gases is regulated by stopcocks, one for each gas, placed near the point of their coming together. The jet points downward. The platinum scraps are first compressed in an iron mould into cylindrical cakes of the weight of 3 or 4 oz. each. Two or three of these are set upon a thin flat fire brick, and heated in a furnace to a white heat.
Being then transferred with the fire brick to a large tin pan like a milk pan, which is well coated within with plaster of Paris, and brought under the jet, this is instantly ignited, and the platinum at once begins to melt. Its surface assumes a brilliant appearance of the purest white, like that of silver, and soon the whole is melted into one mass; but so great is its infusibility, that it chills before it can flow off the flat surface of the fire brick, and it cannot therefore be cast in a mould. For the uses to which platinum is applied this is of no consequence, as the cake of metal is easily hammered into any desired shape, or may be rolled at once into plates, or cut and drawn into wire. With the apparatus of the Drs. Roberts, 53 oz. of platinum were melted into one cake at one operation, lasting only 13 minutes, in April, 1858. This was hammered down without waste, and drawn out into a plate over 40 inches long and about 3 inches wide. Prof. Henry St. Claire Deville of Paris has considerably modified Dr. Roberts's method of melting platinum, and performs the operation in lime crucibles.
Messrs. Johnson and Matheys of London have fused some pounds of platinum and iridium in Deville's furnace. - A compound blowpipe is conveniently made by placing one tube one eighth of an inch in diameter inside another of one half inch diameter. Illuminating gas is admitted at the side of the outer tube and lighted at one end, while the other end is made gas-tight. A current of air is blown by bellows through the inner tube, which at once changes the yellow gas flame to the intense blue blowpipe flame; the combustion is more complete and the flame hotter as the mixture of gas and air is more perfect. This piece of apparatus is called Bunsen's blast lamp; it is used in all chemical laboratories which have gas, and is also used by glass blowers in the manufacture of nice chemical and philosophical apparatus. By this method the effect of a furnace is obtained by chemists for melting the contents of small crucibles in analytical operations. If either or both gases be passed through heated pipes, a still higher degree of heat may be obtained. By substituting oxygen for the atmospheric air, globules of platinum may be instantly melted upon charcoal. This mixture may be conveniently and economically used instead of hydrogen and oxygen for the production of the Drummond light.
The so-called Bohemian glass blowers seem still to prefer the old-fashioned blowpipe, consisting of two gas burners about 10 inches apart, with air jets blowing directly toward each other, by which means the two opposite sides of the glass are heated at the same time.