468 



MINERALOGY. 



Oryctogno- 

 X- 



Brooke'* 

 blowpipe. 



in water, and powder of charcoal added to it, until it be- 

 comes very viscid, when it is to be formed into parallelo- 

 pipeds, and slowly dried. The incombustible supports 

 are, metal, glass, and earth; in the use of all which, one 

 general caution may be given, to make them as little 

 bulky as possible. The best metallic support is platina, 

 because it is infusible, and transmits heat to a less dis- 

 tance, and more slowly, than other metals. A pair of 

 slender forceps of brass, pointed with platina, is the best 

 support for non-metallic minerals, which are not very 

 fusible ; for the fusible earthy minerals, and for the in- 

 fusible ones when fluxes are used, leaf-platina will be 

 found the most convenient. It may be folded like paper 

 into any form, and the result of the experiment may be 

 obtained, simply by unfolding the leaf in which it was 

 wrapped up. Glass supports, are slender glass tubes, on 

 the extremity of which the mineral to be examined is 

 cemented by heating. Earthen supports are, either of 

 small pieces of kyanite, or, when a kind of cuppellation 



Brooke's Blotvpipe. 



Mr. Brooke some time ago contrived a very simple 

 and convenient blowpipe, of which the following de- 

 scription is given by Mr. Neuman. 



" The instrument I have made consists of a strong 

 plate-copper box, perfectly air-tight, three inches in 

 width and height, and four in length, a condensing 

 syringe to force air into the box, and a stop-cock and 

 jet at one end of it to regulate the stream thrown out. 

 'The piston-rod of the condenser works through collars 

 of leather in the cap, which has an aperture in the side, 

 and a screw connected with a stop-cock, which may 

 again communicate with a jar, bladder, or gazometer 

 containing oxygen, hydrogen, or other gases. This 

 communication being made, and the condenser being 

 worked, any air thatjs^required may be thrown into 

 the box and propelled through the jet on the flame. 



"The use of the instrument is very simple. By afew ^^ a ^ ,.._, ., rr 



strokes of the piston, the air is thrown into the cham- ig tQ bg p er f orme ii j they are made of bone-ash, in order 



ber, and forms a compressed atmosphere within. When to absorb t j, e litharge, and other impurities. 



the cock is opened, the air expanding, issues out with The gize of the S p ec j mens to be used in our experi- 



great force, in a small but rapid stream, which, when ^ i :*.,,io f 



directed on the flame of a lamp, acts as the jet from a 

 common blowpipe, but with more precision and regu- 

 larity. The force of the stream of air is easily adjust- 

 ed by opening more or less the small stop-cock ; and I 

 have found, that with a moderate charge, it will re- 

 main uniform for twenty minutes ; opening the stop- 

 cock, or the use of the syringe, will immediately raise 

 it to its first strength. 



These blowpipes are very portable, not liable to in- 

 jury, and answer, I believe, the expectations of all who 

 have tried them, and I have made many of them for 

 different persons. The whole instrument, with a lamp 

 adapted to it, packs up in a small box not more than 

 six inches in length, and four inches in width and 

 height, and there is space enough left for other small 

 articles. I have fitted up boxes rather larger in size, 

 with a selection of tests and other useful articles in ad- 

 dition to the blowpipe, and in this state they form com- 



ii i A _ >r 



Oryctogno- 

 sj. 



plete mineralogical travelling cabinets." 

 Fuel for the Blowpipe 



specimens 



ments, depends in some measure on the magnitude of 

 the flame to which they are exposed. In a blowpipe 

 having an aperture not larger than a fine pin, the 

 piece ought not to be so large as a pea. A good deal 

 also depends on the fusibility of the mineral ; for, if 

 it is very fusible, a much larger piece may be used 

 than when it is difficultly fusible : in the one case, it 

 may be the size of a pea: in the other, it should not 

 exceed that of a pin's head. The heat first applied to 

 investigate the properties of mineral substances should 

 be very low, not exceeding that which exists a little the 

 outside even of the yellow flame. At this temperature 

 the phosphorescence is best extricated, and decrepita- 

 tion for the most part takes place, the fusible inflam- 

 mables begin to melt, and the metallic and most other 

 mineral salts lose their water of crystallization. The 

 yellow flame will raise a mineral to a tolerably full red 

 heat : and it is the temperature best fitted for roasting 

 all the metallic ores. In the still higher degree of heat 

 produced at the point of the interior blue flame, although 

 some minerals still continue refractory, and undergo 



fuel for the 

 blowpipe. 



F tt d for the Blowpipe. ^ ^ e of my kindj yet the greater part are 



The fuel for the lamp is oil, tallow, or wax ; and ot ^ sensibly altered. Some, as pearlstone, enlarge 



these the wax is the best, the oil the worst. The wick 

 should neither be snuffed too high nor too low, and 

 should be a little bent at its summit from the blast of the 

 pipe. The flame, while acted on by the blowpipe, will 

 consist of two parts, an outer and inner : the latter will 

 be of a pale blue colour, converging to a point at the 

 distance of about an inch from the nozzle ; the former 

 will be of a yellowish colour, and will converge less per- 

 fectly. The most intense heat is just at the point of the 

 blue flame. The white flame consists of matter in a 

 state of full combustion, and oxygenates substances im- 

 mersed in it : the blue flame consists of matter in a 

 state of imperfect combustion, and therefore partly de- 

 oxygenates metallic oxides which are placed in contact 

 with it. 



, 



very sensibly altered. Some, as pearlstone, enlarge 

 very considerably in bulk at the first impression of the 

 heat, but are with difficulty afterwards brought to a 

 state of fusion : others are melted only on the edges 

 and angles; and in some, a complete fusion takes 

 place. 



Fluxes for Minerals exposed to the Blowpipe. 

 In examining earthy minerals with the blowpipe, no 

 fluxes are required ; whereas to most of the metallic ores 

 fluxes will be found at almost all times a very useful and 

 often a necessary addition. The ores of the difficultly 

 reducible metals, such as manganese, cobalt, chrome, 

 and titanium, are characterised by the colours which 

 the oxides give to glass. In all these cases, therefore, 

 glassy fluxes must be largely made use of, both to dis- 

 solve the earthy matter with which the oxides are ge- 



r 



Fluxes for 

 minerals 

 exposed to 



Supports 

 for mine- 

 rals expo- 



Supports for Minerals exposed to the Blowpipe. soive me ean.iiy umi.vci .*.. - - 



Various substances are employed for supporting the nerally combined, and to furnish t t ,od \y,v, -ith J JU e or 



mineral, when undergoing the action of the blowpipe, no colour of its own, yhich may ^vj n cl^uttic* em 



rals expo- These are of two kinds, combustible and incombustible, ly dilute, the inherent colour o oxide ntn 



,ed to the The comb ustibl e support, used chiefly for ores, is char- object is not only *> dissolve he o J^JJ^JNJJ 



blowpipe. coa] The dosest '^ined and soundest pieces of char- time to retain it at a high state of oxidrt on the flux ,em 



coal, of elder or lime-tree, are to be selected ; or a sup- poyed should be either n Tborax formed by 



port may be made of well pulverised and heated char- glass of borax, or, still better ml "i^S its 



coal and gum tragacanth. The gum should be dissolved dissolving common borax in hot water, n< 



