•123 



(Ff 0^1; numerous esperiraeuts, of the qualities of diife- 

 fffit compositions, made by several persons, it appears, 

 tjiat no, cpmhinations, of any other metals or semi-metals, 

 are fit for specula, except those of copper, brass, tin, 

 silvea-, and &rsenic. I tried no semi-metal, except the lat- 

 ter, whicii s'hitens copper, and unites intimately with it; 

 ^e;c^use.it is stated, in the treatise of the Art of Assay- 

 itig, by the obsei"vant and accurate Cramer, that all the 

 semi-metals rise in flowers, during the fusion : which would 

 certainly make the metal porous. On this account, I 

 •would have rejected tlie brass, because of the zinc con- 

 tained in it; but that it seemed to render the compo- 

 sition whiter, and less apt to tarnish, than it would be 

 without, j.t.i It will have little tendency to rise in flowers, 

 if thi6: specultim-metai be fused, with the lowest heat re- 

 quisite, and if the brass be of the best kind; because, in 

 this, the jzinc is more perfectly united w'ith the copper, 

 and both are purer. I used, for this purpose, the brass 

 of piurwirec and, because t'he quantity of it was only 

 lili^';$)ne eighth part of the copper employed, which, I 

 jipjagined, would receive too fierce a heat, if put alone into 

 the ujelted copper; I first added to the brass, in fusion, 

 about an equal quantity of the tin, and put the mass 

 ppJUl ii?t<)>vith«; ijj^elted- /copper ; supplying afterward the re- 

 mainder oft^the lin, and then the argenic; the whole be-^ 

 iftg generally anl IhQ I [following proportion: vi.z^-S^-^ ^iii 

 best bar copper, previously fluxed Avith the black flux, 

 ^|";tw0:.p3rt8 taitai,-;; laud' one of nitre, 4 parts brass, 16^ 

 > 1;. /(J parts 



