f *9 2 1 



then to be directed on the matter i tie If, and ir? 

 the fait fpreads too much about, leaving the proof 

 almoft alone, it may be brought to it again by 

 blowing the flame on its extremities, and direct- 

 ing it towards the fubject of the experiment. 

 In the afiays made with this fait, it is true, we? 

 may find if the mineral bodies which are melted, 

 •with it have. been diffolved by it or not •, but we. 

 cannot tclt with any certitude whether this is done 

 haftily and with force, or gently and : flowly -,, 

 whether only- a lefs or a greater part of the matter 

 has been difiblved $ nor canut be well diftineruilhed 

 if the matter has imparted any weak tincture to • 

 the flag*,, becaufe this ialt always bubbles upon 

 the charcoal during the experiment, nor is it clear 

 when cool*, fo that fcarce any colour, except it be 

 a very deep one, can be difcovered, although 

 it may fometimes be coloured by the matter that^ 

 has been tried. 



SECT. XXI. 



The other two falts, viz. the Borax, and. the 

 Sal fuftble microcofmicum, are very well adapted 

 ro thefe experiments, becaufe they may by the 

 flame be brought to a clear uncoloured and trans- 

 parent glafs i and as they have no attraction ta> 

 the charcoal, they keep themfelves always upon; 

 it in a round globular form. The Sal; fufibile mi- 

 crocofmictini is very fcarce, and' perhaps not; to, 

 be met with in the ftiops--i.it is made of urine : 

 Mr. MargrarT has given a full account of its pre- 

 paration in the Memoirs of" the Academy of- 

 Scleiices at Berlin, 



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S E C T. 



