The methods of chemical analysis may be classified according to the type of reaction: (I) dry or blowpipe analysis, which consists in an examination of the substance in the dry condition; this includes such tests as ignition in a tube, ignition on charcoal in the blowpipe flame, fusion with borax, microcosmic salt or fluxes, and flame colorations (in quantitative work the dry methods are sometimes termed " dry assaying "); (2) wet analysis, in which a solution of the substance is treated with reagents which produce specific reactions when certain elements or groups of elements are present.
The first work on this application of the blowpipe was by G.
The simplest and oldest form of blowpipe is a conical brass tube, about 7 in.
Sulphates may be detected by heating the salt mixed with sodium carbonate on charcoal in the reducing flame of the blowpipe; sodium sulphide is thus formed, and may be identified by the black stain produced if the mass be transferred to a silver coin and then moistened.
Cadmium salts can be recognized by the brown incrustation which is formed when they are heated on charcoal in the oxidizing flame of the blowpipe; and also by the yellow precipitate formed when sulphuretted hydrogen is passed though their acidified solutions.
It fuses easily in the electric arc. It oxidizes superficially when heated, but fairly rapidly when ignited in an oxidizing blowpipe flame, forming a black smoke of the oxide.
The introduction of the blowpipe into dry qualitative analysis by Axel Fredrik Cronstedt marks an important innovation.
- For Blowpipe Analysis: C. F.
Tin compounds when heated on charcoal with sodium carbonate or potassium cyanide in the reducing blowpipe flame yield the metal and a scanty ring of white Sn02.
The introduction of acetylene dissolved under pressure in acetone contained in cylinders filled with porous material drew attention again to this use of the gas, and by using a special construction of blowpipe an oxy-acetylene flame is produced, which is far hotter than the oxy-hydrogen flame, and at the same time is so reducing in its character that it can be used for the direct autogenous welding of steel and many minor metallurgical processes.
Soldering, brazing and the blowpipe in the Cordilleran provinces are suspected, but the evidence of their existence must be further examined.
The artificers in gold and silver melted the metals by means of a reed-blowpipe and cast them solid or hollow, and were also skilled in hammered work and chasing, as some fine specimens remain to show, though the famous animals modelled with gold and silver, fur, feathers and scales have disappeared.
BLOWPIPE, in the arts and chemistry, a tube for directing a jet of air into a fire or into the flame of a lamp or gas jet, for the purpose of producing a high temperature by accelerating the combustion.
The blowpipe has been in common use from the earliest times for soldering metals and working glass, but its introduction into systematic chemical analysis is to be ascribed to A.
In blowpipe work only two of these four parts are made use of, viz.
To obtain a good oxidizing flame, the blowpipe is held with its nozzle inserted in the edge of the flame close over the level of the wick, and blown into gently and evenly.
Various materials are used as supports for substances in the blowpipe flame; the principal are charcoal, platinum and glass or porcelain.
Platinum is employed in oxidizing processes, and in the fusion of substances with fluxes; also in observing the colouring effect of substances on the blowpipe flame (which effect is apt to be somewhat masked by charcoal).
The mouth blowpipe is unsuitable for the production of a large flame, and cannot be used for any lengthy operations; hence recourse must be made to types in which the air-blast is occasioned by mechanical means.
The hot blast blowpipe of T.
For the applications of the blowpipe in chemical analysis see CHEMISTRY: Analytical.
Alumina itself is so refractory that it cannot be melted save by the oxyhydrogen blowpipe or the electric arc, and except in the molten state it is not susceptible of decomposition by any chemical reagent.
Fizeau he carried on a series of investigations on the intensity of the light of the sun, as compared with that of carbon in the electric arc, and of lime in the flame of the oxyhydrogen blowpipe; on the interference of heat rays, and of light rays differing greatly in lengths of path; and on the chromatic polarization of light.
It is infusible before the gas blowpipe, but in the oxyhydrogen flame fuses to a clear colourless glass, which has a hardness of 5 and specific gravity 2.2.