Page:The American Cyclopædia (1879) Volume II.djvu/769

 BLOWPIPE 749 analysis of many metallic compounds. The compound or oxyhydrogen blowpipe is an ap- paratus invented by Dr. Robert Hare of Phila- delpbia, in the early part of the present cen- tury. By this a mixture of oxygen and hy- drogen is made to produce the jet, which being inflamed just beyond their point of mixing, an amount of intense heat is evolved far exceed- ing what had ever been before obtained. Sub- stances 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 light- houses, and his name has since been applied to the light, which was first obtained and no- ticed by Dr. Hare. The first arrangement adopted by Dr. Hare was to collect each gas in a separate reservoir, and cause them to be dis- charged by separate jets at the point of com- bustion. 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 explo- sion by a retrocession of the flame into the sin- gle 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 ex- hibited a specimen of the metal, weighing be- tween 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 suffi- ciently capacious to contain it all. He also obtained platinum directly from the crude pro- duct 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 consider- able pressure, the effect was still further in- creased. With this modification, Prof. Clarke, of the university of Cambridge, England, re- peated 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 man- ganese. 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 plati- num 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 Ibs. to the square inch, forced the gases through metallic pipes to the apparatus con- nected 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 be- ing 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 i by J 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 fur- nace 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 instant- ly ignited, and the platinum at once begins to melt. Its surface assumes a brilliant appear- ance 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