LABORATORY. 



urged ; but these instruments seem to be 

 rather toys than of use to the actual che- 

 mical investigator. It appears preiera- 

 ble to use bellows, as the enamellers do, 

 where an extensive application of this im- 

 plement is required ; though in this case 

 the desirable requisite of portability is 

 lost sight of. 



The bodies intended to be heated by 

 the blow-pipe must not, in general, ex- 

 ceed the size of a pepper-corn, unless 

 bellows and a very large flame be used. 

 The proper supports are, either a piece 

 of smooth, close-grained charcoal, for 

 such bodies as are not subject to an al- 

 teration of their properties, from the in- 

 flammability of the coal, as might be con- 

 trary to the nature of the investigation. 

 This support is therefore most frequent- 

 ly used ; as it is properly adapted for sa- 

 line, earthy, and many metallic bodies. 

 The other support consists of a spoon, 

 somewhat less than a quarter of an inch 

 in diameter, made of a metal not sub- 

 ject to oxydation ; that is to say, pure 

 gold, silver, or platina, or such a mix- 

 ture of these metals as might be found 

 to be least deficient in the requisite de- 

 gree of hardness, which gold or silver 

 alone does not possess. Bergman advis- 

 ed to add one-tenth of platina to a given 

 mass of silver. There is, however, no 

 very considerable inconvenience resulting 

 from the use of a small spoon, either of 

 gold or of silver ; and platina possesses 

 every quality which can be wished for. The 

 small metallic spoon must of course be 

 properly fixed in a socket of metal, pro- 

 vided with a wooden handle. 



Very small or pulverulent substances 

 are apt to be carried away by the current 

 of flame. These may be secured by 

 making a small hole in the charcoal, in- 

 to which the powder is to be put, and 

 covered with another small piece of char- 

 coal, which partly protects them from the 

 flame. Some experiments of reduction 

 are made by binding two small pieces 

 of charcoal together, cutting a channel 

 along the piece intended to be the un- 

 dermost, and making a cavity in the 

 middle ot this channel to contain the sub- 

 ject matter of examination. With this 

 apparatus the flame is urged through the 

 channel between the two pieces of coal, 

 and violently heats the substance in the 

 cavity, which may be considered as a clos- 

 ed vessel. 



A great number of mineral bodies are 

 not fusible by mere flame, urged by com- 

 mon air through the blow-pipe ; though 



oxygen gas subdues most bodies. See 

 GAS ojcygen. 



Whenever, therefore, the fusion of any 

 refractory substance is to be attempted, 

 some other substance must be added 

 which is more fusible, and capable of 

 dissolving the former. These solvents in 

 the dry way, are distinguished by the 

 name of fluxes, and, like the solvents 

 used in the humid way, are mostly sa- 

 line. It may easily be imagined, that 

 the nature of the products will greatly 

 vary, according to that of the flux, which 

 enters into combination with them ; and 

 accordingly they are varied in experi- 

 ments, as well as in operations, in the 

 large way. The blow-pipe experiments, 

 though conducted upon the same prin- 

 ciples as those upon a larger scale, dif- 

 fer nevertheless from them in two par- 

 ticulars ; namely, that the whole of the 

 phenomena are visible throughout, and 

 that the residues are of no value, other- 

 wise than as they serve to indicate facts. 

 For these reasons, every flux, without 

 exception, might be used with the blow- 

 pipe, provided it were not of such a 

 nature as to sink into the charcoal. We 

 may therefore select a certain small 

 number of the most convenient fluxes, 

 and note the effects which they respec- 

 tively produce upon the various mineral 

 bodies ; and these will serve as indica- 

 tions to enable the chemical enquirer 

 to distinguish them again with a great 

 degree of accuracy, not to mention, that 

 he may also derive much advantage, 

 with regard to the more extensive ope- 

 rations he might be disposed to under- 

 take. A considerable part of this pre- 

 liminary labour has already been per- 

 formed by Engestrom, Bergman, Mon- 

 gez,, and others ; and it is now become 

 usual for chemists, among their other 

 experiments on minerals, to mention their 

 habitudes with the blow-pipe. 



The fluxes which have obtained the ge- 

 neral sanction of chemists, on account 

 of the extensive use they have been ap- 

 plied to by Bergman, are phosphoric 

 acid in the dry or glassy state, soda, 

 and borax, or the native borate of soda. 



LABOUR, in general, denotes a close 

 application to work or business. Among 

 seamen a ship is said to be in labour when 

 she rolls and tumbles very much, either a 

 hull under sail, or at anchor. It is also 

 spoke of a woman in travail, or child-birth. 

 See MIDWIFERY 



LABRADOR stone, in mineralogy, is of 

 a grey colour, passing into a dark ash. 



