2 The Subject Propounded.' 



the fubjecl, either as a chemical operator, or as 

 a writer. Tho* indeed., to be ingenuous, fome- 

 thirVg of difguft and indifference interpofed ; as 

 generally is the cafe in a work of conliderable 

 length, and carried on amidft a diflipation of 

 thought. Neverthelefs, fuch as it is, I have fpent 

 fo much time and been at fo great expence in 

 ihis performance, that I know not whether, under 

 the fame circumftances, I mould ever again be 

 able to execute fuch another. 



2. The importance of the fubject: more than a 

 little time Was required to procure from the feveral 

 countries and mines their feveral fpecies or fam- 

 ples; and the Englifh famples, difpatched for 

 me by the celebrated Dr. Woodward, never came 

 to hand. A repetition of fome experiments was 

 alfo neceiTary, efpecially to determine the very 

 ilow vitrioiifation of feveral forts of pyrites^ fur- 

 ther to confirm my opinion of this mineral bo- 

 dy, and to procure the remarks and fentiments 

 or my correfpondents concerning it. 



3. My method of treating the fubjeft : it was 

 not my intention to fill up my book with tran- 

 fcripts from authors. Nor indeed had I ever fo 

 great a mind to it, could I well •, feeing nothing 

 ufeful to my purpofe could be found in them. 



But is it readily to be imagined, that the treat- 

 ing a fubject in the laboratory, and the dif- 

 covering a new truth, fhall require no more 

 time than the writing over a few leaves of pa- 

 per ? I may truly aver, there is many a truth 

 and many a very fhort proposition, which I was 

 obliged to retain in my thoughts, through the 

 courfe of this enquiry, as it were in labour, to 

 bring them to the birth, here fet down in the com- 

 pafs of a few lines, that employed me not only 

 days and Weeks, but even months to afcertain. 

 And yet, after all, fome others remain behind, 



on 



