Page:Encyclopædia Britannica, Ninth Edition, v. 3.djvu/857

Rh ganate of sodium, a fine green colour. (For particulars of the behaviour of different minerals before the blowpipe, see the detailed description in the article .) Of late years the spectroscope has been successfully used in connection with blowpipe operations, in the detection of certain of the rarer metallic elements. The blowpipe was first applied in the quantitative deter mination of metals by Harkort in 1827, and was brought to a high degree of perfection by Plattner. The methods are substantially those adopted in the assay of ores on the large scale in the wind furnace or muffle, thin cap sules of clay or cavities in charcoal blocks being substituted for crucibles, and steel basins faced with bone ash, for cupels, in silver and gold assaying. From the small size of the beads obtained, especially when the ores of the pre cious metals are operated upon, the results are often such as cannot be weighed, and they are then measured by a tangent scale, and the weight computed from the observed diameter. This method, devised by Harkort, gives very accurate results when carefully used, but owing to the difficulty of sampling the minute quantities operated upon so as to represent the bulk of the mineral fairly, the quantitative blowpipe assay has not made much progress. Perhaps the most useful quantitative application is in the determination of nickel and cobalt. This depends upon the fact that when the compounds of these metals, as well as those of copper and iron, with arsenic, are melted in contact with an oxidizing flux, such as borax or salt of phosphorus, iron is first taken up, then cobalt, and next nickel, and finally copper ; and as the oxides of these metals give very different colours to the flux, we are enabled by examining the slag to detect the exact moment at which each is removed. For the details of the process the reader is referred to Planner s work. I 1 10. 2. Blowpipe witn Bellows. Among the various arrangements which have been con trived for supplying air to the blowpipe otherwise than with the mouth, we may select that represented in the annexed figure (2) as one which is generally sufficient for practical purposes It will be seen that the jet i is sup ported on a slide which can be fixed by screwing in any direction and at any height on the rod 5, which is jointed on the board 6. The blast can thus be adjusted variously, according to the position given to the blowpipe lamp a, which is of the form devised by Berzelius. The bellows B, the tube k. and the reservoir B, are of vulcanized india-rubber, v and v arc valves. The bellows being alternately compressed (with hand or foot) and allowed to expand, air is driven into the reservoir, and a fresh supply admitted into the bellows through v. After a few trials a constant blast may thus be maintained through the nozzle. Fig. 3 - ... For glass-blowing ordinary coal gas is the best com bustible, as the flame can be well controlled by a stop cock, and requires no trimming. The nature of the apparatus will be understood from fig. 3, which shows the burner in horizontal section. The tube ab is screwed into another tube which is con nected with the gas pipe &amp;lt;?/. mn and op are two annular disks which support the pipe ab; they have a series of open ings round their edges, to admit a uniform flow of gas to the narrow annular mouth between the two tubes where it joins the blast. The stop cock / regulates the supply of gas. The wind, supplied by double bellows fixed under the table, is sent through a lead pipe on which brass nozzles of various width can be screwed, opening into ab; the finer nozzles being pushed up nearly to the end of this. Elastic tubing may sometimes be used with advantage for the connections. A modified form of the apparatus is suit able for ordinary blowpipe researches of the mineralogist or chemist (see Plattuer s work, 4th edition), and the appara tus used in hand-soldering of metals and other operations of the workshop is on the same principle. With suit- M able trunnions the blowpipe may be made to point in any direction as required. Fig. 4-... The soldering lamp of tinners is an example of the osolipile, an instru ment which deserves some notice here. The spirit lamp a (fig. 4) is inserted at the bottom of a sheet-iron cylinder MX, which is open on one side, as shown. The upper part of the cylinder supports a strong cup of hammered metal, with an opening for spirits at the top (closed by a screw or cock), and a bent tube coming down from its upper part, through a slit in the cylinder to the back of the flame. The weak spirits which are put in the cup are caused to boil by the heat of the lamp, and the vapour, escaping through the bent tube, pro duces a jet of very hot flame. (The cup is shown separately in fig. 5). Similar advantage is gained by causing air to pass through a quantity of some soluble hydrocarbon before it goes to the nozzle of a blowpipe. FlG - 5. Cap of f,g. 4. There are several forms of apparatus in which water- pressure is utilized for supplying a steady blast to the blowpipe. One of these consists of a tin case, with an oblique, partition reaching nearly to the bottom. The case is filled nearly three-fourths with water. Air is blown into the compartment ohich narrows upwards (and with which the nozzle is connected above) by a pipe reaching nearly to the bottom. This air rises through the water and accumulates above it, forcing the water up into the other compartment, which communicates freely with the outer air. The difference of water-level in the two cham- 