(5*^ Metallic Compofilionsfor Specufums; ' 



APPENDIX. 



An Aceount offeveral Compofttms of Metals and Semi-Metals, on nvhlch Trials ivere made ft. 

 find out the mofi proper Mipctiire for the Specula of RefieBing Telefcopes. By the Rett^ 

 John Edwards, B. A. 



1. COPPER and tin* equal parts; very bad, foft, andof a blue color^ 



2. Copper with arfenic i ; but little different from the firft. 



3. Tin 2, copper i ; much vvorfe than the preceding ones^ 



4. Copper 32, tin 16, arfenic 4;t black and brittle. 

 5-. Copper 6, tin i|, arfenic i ; very indifferent. 



6. Copper 32, tin 14, arfenic 2 ; a very good metal. 



7. Copper 32, tin 13!, arfenic 1 ; not quite fo good as the fixth.. 



8. Copper 32, tin 13^, arfenic i-i ; a good metal. 



9. Copper 32, tin 15, arfenic 2; much better than any of the above. 



10. Copper 6, tin 2, arfenic i ; compa£V, but very yellow when polifhed.. 



11. Copper 3, tin i~; compa(St, and whiter than the tenth. 



12. Copper 32, tin 144-; a pretty good metal, but polifhes too yellow. 



13. Copper 32, tin 15, arfenic 2, flint glafs J in powder 3; very bright, but rotten. 



14. Brafs 6, tin i ; compaft, but too yellow. 



15. Two parts of n"> compofilion, and i part of 14 compofition ; compafl;, but muchi 

 too yellow when poliflied. 



1(5. Brafs 5, tin i ; fomewhat whiter than the 14th. 



17. Brafs 4, tin I ; a good metal, but rather yellow. 



18. Brafs 4, tin I, with arfenic -rV > whiter than 17. 



19. Brafs 3, tin i § ; will not polifli well. 



20. Brafs 2, tin i ; of a fparry nature. 



21. Tin 3, brafs I ; too foft, being only a kind of hard pewter. 



22. Brafs and arfenic equal parts ; a dirty white colour. 



23. Brafs, copper, and arfenic equal parts j a dingy white. 



• By tin, I always mean grain tin, 



+ The nitre was added to fix the arfenic. 



X Flint glafs was added as a flux. See Shaw's Chemiftry, p. 255. Note, the loth is the compoGtioni 

 of Sirlfaac Newton. See Appendix to Gregory's Optics, p. 121. The nth, 14th, and 15th are the com» 

 pofitions of Mr. Mblyneux. See Smltii's Optics, Vol. II. p. 304. And the lith is the compofition of- 

 Mr, Mudge, See Philofophical Tranfaftions, Vol. LXVII. p, 298. 



§ Thefe compofjtions are mentioned by Neri and Kunckell in Neri's art of glafs making. Surely they, 

 never tried thofe compofitions themfelves, but took them upon the report of other authors ;' as the 19 will 

 not take a good luftre, and the ii is very foft, like hard pewter, therefore highly improper for fpecula,, 

 which Ihould be as hard as polJiblc. 



24. Brafs. 



