112 On the polishing of Glass, and on 



this paper cannot be submkted to too severe a scrutiny; 

 and no judge can. be more rigid or more competent than the 

 very person who was the first to doubt my former experi- 

 ments. But it is necessary to be observed by whoever shall 

 think them worth the trouble of verifying, that even these 

 experiments are Hable to fail, unless proper precautions are 

 used ; that I liave never operated upon less than one hun- 

 dred grains ; and that the results which I have stated, how- 

 ever simple they may appear, have been the constant labour 

 of some weeks. 



POSTSCRIPT. 



Since this paper was written, Dr. Wollaston has pub- 

 lished some experiments upon platina. He has found that 

 palladium is contained in very small quantities in crude 

 platina. This fact was mentioned to me more than a year 

 ago by Dr. Wollaston. I have not yet seen a copy of his 

 paper ; but I shall merely observe here, that, whatever be 

 the ijuautity of palladium found in a natural state, no con- 

 clusion can be drawn as to its being simple or compound. 

 Nothing is more probable than that nature may have formed 

 this alloy, and formed it much better than we can do. At 

 all events the amalgamation to which platina is submitted 

 before it reaches Europe^ is sufficient fo account for a small 

 portion of palladium. 



XVII. OhscrvatioTts on the polishing of Glass, and on ths 

 Amalgam used for silvering Mirrors. By B. G. Sage *. 



JlIaving been consulted in regard to the bad effects of 

 some calces or red oxides ni" iron, which alter the surface 

 of glass bv renderino- it dull and yellowish, I analysed these 

 calces of iron, and found out the cause on which this defect 

 depci'.'i^;. Red calx or oxide of iron, called cokothar, is 

 employed with water for giving the last polish to glass in- 

 tended for mirrors. 



Were not the oxide or calx of tin, commonly known by 

 the name oi' pul/i/, so dear, it would be far preferable to red 

 calx or oxide of iron, obtained by the decomposition of mar- 

 tial vitriol, either by calcining it in a fire proper for disen- 

 gaging the arid or decomposing the sulphate of iron by 

 marine salt. In the latter case, the red oxide or calx of 

 Iron retains a little of that salt, which is of no hurt in the 



* Fiom the Journal de Pliysiquc, I'hermidor, au 12. 



polishing 



