BLOW′PIPE

(blō′-). Syn. Chalumeau , Fr.; Löthrohr , Ger. An instrument by means of which the flame of a candle or lamp, or a gas-jet, is directed upon any substance placed to receive it, which is thus subjected to an intense heat. The blowpipe is to the artist and the experimentalist what the wind-furnace is to the artisan; but it is proportionately more powerful, convenient, and economical. Beginners are usually unable to maintain a continued stream of air from the jet of this instrument, although the doing so is really a very simple affair. The operation merely depends on a little artifice in using it, which is more difficult to describe than to acquire. The effect intended to be produced is a continual stream of air for many minutes, if nece ary, without interruption, even for an instant. This is done by simply applying the tongue to the roof of the mouth, so as to interrupt the communication between the mouth and the pa age of the nostrils; by which means the operator is at liberty to breathe through the nose, at the same time that by the muscles of the lips he forces a continued stream of air from the anterior part of the mouth through the blowpipe. When the mouth begins to be empty it is replenished by the lungs in an instant, while the tongue is withdrawn from the roof of the mouth, and replaced again in the same manner as in pronouncing the monosyllable tut. In this way the stream of air may be continued for a long time without fatigue, provided the flame be not urged too impetuously; and even should it be so urged no other inconvenience will be felt than that of slight fatigue of the muscles of the lips. at the tip of the outer white flame, which has also the property of rapidly burning or oxidising substances placed in it which are susceptible of such a change; and it is hence commonly called the OXIDISING FLAME . The interior blue flame is, for a like reason, called the DEOXIDISING or REDUCING FLAME , as it po e es the property of extracting oxygen from most bodies capable of being so affected. Substances to be submitted to the action of the blowpipe-flame are placed on a support, which is either a piece of charcoal, or a wire or small spoon of platinum, gold, or silver, as the case may require. Sometimes a plate of cyanite is used. Pine-wood charcoal is preferred for this purpose; and the sides, not the ends of the fibres, are presented to the flame. When a very intense heat is required, the substance operated on should not exceed the size of half a peppercorn. Several characteristic colour reactions may often be obtained in the examination of a substance for analysis, by fusing a small portion of it, with a bead of microcosmic salt, and exposing it for some time to the outer flame of the blowpipe. If the substance di olve readily in the salt and rather copiously to a clear bead whilst hot , and is of a blue colour by candle light inclining to violet, it denotes COBALT . If it be green, upon cooling blue; in the reducing flame after cooling, red— COPPER . If green, particularly fine on cooling, unaltered in the reducing flame, CHROMIUM . If brownish red, on cooling light yellow or colourle ; in this reducing flame, red whilst hot, yellow whilst cooling, then greenish— IRON . If reddish to brownish red, on cooling yellow to reddish yellow or colourle ; in the reducing flame unaltered— NICKEL . If yellowish-brown, on cooling light yellow or colourle ; in the reducing flame almost colourle , and blackish-grey on cooling— BISMUTH . If light yellowish to opal, when cold, rather dull; in the reducing flame whitish-grey— SILVER . If amethyst-red, especially on cooling; colourle in the reducing flame, not quite clear— MANGANESE . If the bead remains clear on cooling, ANTIMONY , ALUMINA , ZINC , CADMIUM , LEAD , LIME , and MAGNESIA are indicated, the latter five when added in somewhat large proportion to the microcosmic salt, give enamel white beads. The bead of oxide of LEAD saturated is yellowish. If the bead becomes enamel-white on cooling, even where only a small portion of the powder has been added to the microcosmic salt— BARYTA and STRONTIA are indicated. If the substance di olves in the microcosmic salt slowly and only in small quantity, the bead being colourle and remaining so after cooling, the undi olved portion looking semi-transparent, and if upon the addition of a little sesquioxide of iron it acquires the characteristic colour of an iron bead—this denotes SILICIC ACID . For producing extreme degrees of heat the flame is blown with a jet of oxygen gas, the instrument being then called an OXYGEN BLOWPIPE ; or a mixture of oxygen and hydrogen is burned, when it is called an substance can stand exposure to it, even the most refractory native compounds being immediately fused. Gold is volatilised, and iron is rapidly consumed the instant it is placed in the flame. IMG:596405606043057898_i336.png: 1. Hemming’s safety-jet for the oxy-hydrogen blowpipe. a , Pipe conveying oxygen gas. b , ” hydrogen gas. c , Ball stuffed with fine wire-gauze. e , Jet (internal diameter 1-80th of an inch). 2. Black’s blowpipe. 3. Bergman’s blowpipe. 4. Pepy’s blowpipe. 5. Wollaston’s blowpipe. 6. Oxy-hydrogen blowpipe. The principal varieties of the blowpipe in general use are figured in the engravings above. Beside the above there are several other varieties of the blowpipe occasionally employed; one in which the air is expelled by the pre ure of a column of water, and hence called the HYDROSTATIC BLOWPIPE ; another, in which the flame is blown with the vapour of boiling alcohol, is named the SPIRIT-BLOWPIPE .