[ 1*3 3 



SECT. XII. 



Whenever any thing is to be tried, one mult 

 not begin immediately with the Blow-pipe -, fomc 

 preliminary experiments ought to go before, by 

 which thole in the fire may afterwards be directed. 

 For inftance, a done is not always homogeneous, or 

 of the fame kind throughout, although it may ap- 

 pear to the eye to be fo : The magnifying-glafs is 

 therefore neceffary, to difcover the heterogeneous 

 particles, if there be any ^ and thefe ought to be 

 ieparated, and every thing tried by itfelf, that 

 the effects of two different things, tried together, 

 may not be attributed to one alone. This might 

 happen with fome of the finer mica* which are 

 now and then found mixed with fmall particles of 

 quartz, fcarcely to be perceived by the eye. The 

 Trapp, (in German Scbwartzftein) is alfo ibmetimes 

 mixed with very fine particles of Feltfpat (Jpatum 

 fcintillam) or of Calcareous Spar, &c. After this 

 experiment follows that, to try the hardnefs of thit 

 flone in queftion with the fteel. The Flint and 

 Garnet-kinds are commonly known to flrike fire 

 with the ftcel •, but there are alfo other flones, 

 though very feldom, found fo hard as to flrike fire : 



for the acids, mentioned Seel. Ixii. is reduced to lefs than a 

 fourth of its original bulk, being exattly of the fame fizewith 

 the above. It contains two fmall matrafTes [Tab. I. fig. 4.] 

 for making folutions ; a trough [Tab I. fig. 5.] for warning 

 the ore after its being pounded ; and the three fmall bottles 

 w'tli double fteppers, for the nitrous, ?nuriatic t and -vitriolic 

 Acids, have their refpective initials cut on each. 



Boh thefe Pccket-Lab >ratories, made in the reatefl manner 

 by an ingenious artiii, may be had ready furnifhed with the 

 purelt acid', &c at the General Office of Bufinefs> Arts and 

 tfrade, opened for the piefenr at No. 98, Woou-Street, 

 Chea^fide, and or:ly there, for very reafonable prices. 



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