Page:The American Cyclopædia (1879) Volume II.djvu/768

 T48 BLOWPIPE instruments and some tests, all of which may he easily transported, serves the purpose of a portable laboratory. In skilful hands all min- eral substances may be determined and a com- plete qualitative analysis made by it; and by the improvements introduced by Prof. Plattner, many quantitative analyses may be effected for practical purposes. The blowpipe was first ap- plied 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 classi- fication of minerals according to their chemical composition. This hook was first published in 1758, and was translated into English hy 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 sci- entific men was thus directed to its great use as an analytical instrument, hut the difficulty of learning to apply it, without practical instruc- tion, prevented its being so generally received as it deserves to he ; and had not the Swedish chemists continued to employ and improve it, it might after all have fallen into disuse. Berg- man found it very serviceable in his chemical researches, and Gahn, who assisted him, car- ried its use to a higher state of perfection than had hefore been attained. Berzelius enjoyed the most friendly intercourse with this remark- able 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 as- certained the nature of substances not recog- nizable hy their external properties. Long before the subject of vegetable substances con- taming 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 1J inch to its capillary extremity. The object of the cylinder is to intercept the moisture of the breath, which without such an arrangement asses through the tube, and is projected in _rops 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, accom- pany the instrument, and are changed as the fiamc is desired to be more pointed and intense, or of less intensity and to cover a larger surface. Considerable practice is required to blow con- tinuously 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 attain- ment, but is at last caught, one knows not how, and is never afterward lost. Quick's gas blow- pipe, 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. 3. 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 pro- cesses 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 gen- eral. The methods adopted by Prof. Plattner for separating the minute particles, and ascer- taining their weights, are of great ingenuity and simplicity, and valuable for the prompti- tude with which they may be used ; but to be successfully practised, they require long and patient use of the instruments. The little glo- bules of gold and silver extracted from their combinations by the blowpipe are often too small to be weighed, but their quantity is de- termined 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 Riiger, 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