| Description | ' About the Metalline composition for an object - speculum to his reflecting Telescope. '
' Sir
Not having tryed many proportions of the Arsenick and Metall, I am not assured which is absolutely best, but there may conveniently be used any quantity of Arsenick equalling in weight betweene a sixt and eight part of the Copper. A greater proportion makes the metall brittle.
The way which I used is this : I first melted the Copper alone, then put in the Arsenick, which being melted I stirred them a little together, bewaring in the meanetime that I drew not in breath neare the pernicious fumes. After that I put in the Tin, and again, so soon as that was melted, which was very suddenly, I stirred them well together, and imediately powred them off.
I know not whether by letting them stand longer on the fire aftert the Tin as melted, a higher deree of fusion would have made the metall porous ; but I thought that way I proceeded to bee safest. In that metall which I ssent to London there was noe Arsenick, but a small proportion of silver ; as I remember 1 in 3 of metall. But I thought the silver did as much harm in making the metall soft and so lesse fitt to bee polished, as good inrendering it white and luminous. At another time I mixed Arsenick i, Copper vi, and Tin ii. And this an acquaintance of mine hath polished better than I did the other. ' |