1 14 Ohservaiions on the polishing of Glass, c^c. 



extended the number of the plates is doubled, so that thc\? 

 amount sometimes to eiffhtv or more. They are theii 

 smoothed with the flat side of the hammer, and are beat 

 till they acquire the length of six or seven feet, and the 

 breadtli of four or five. The small blcx-k of tin from which 

 they are formed is at first ten inches long, six in breadth, 

 and a line and a quarter in thickness. 



When the leaves are of less extent, and thin, from eighty 

 to a hundred of them arc smoothed together. 



Tin extracted from the amalgam which has been em- 

 ployed for silvering glass, exhibits a remarkable peculiarity. 

 When fused in an iron pan, its whole surface becomes co- 

 vered with a nudtitude of tctraedral prismatic crystals two 

 or three lines in length and a quarter of a line in thickness. 

 The interior of these pieces of tin, when cut with a chi- 

 sel, have a grayer lint than pure tin, which is as white as 

 silver. The latter crystallizes also by cooling; but it re- 

 quires care. When it begins to be fixed, decant the part 

 •which is still in fusion, and there will remain at the bottom 

 of the ciucible beautiful crystals of a dull white colour, 

 which appeared to nie to be cubes or parallelopipedons. 



The peculiar and constant crystallization of tin taken 

 from the an)algam of mirrors, the leaden gray colour which 

 the mass of this metal had, and the mystery made of the 

 preparation of this tin, induced n)e to try whether I could 

 not discover by analysis the substance mixed with it. 



Having calcined this tin in a test, it was reduced to a 

 powder of a delicate red colour, and increased in its weight 

 l-25th. The magnet attracted particles of iron, tlie result 

 of the hanmiering. It appears that this metal concurs to 

 produce the crystallization of the tin, and the singularity 

 exhibited by the solution of its oxide in nitric acid. At 

 first, nothing is manifested but a slight effervescence, which 

 soon subsides ; but four or live minutes after, the mixtures 

 become very hot, and a stronger effervescence takes place, 

 accompanied with a great deal of nitrous gas, which is dis- 

 engaged with an explosion, and there remains in the glass 

 a magma of a pale red colour. 



The white oxide of tin, mixed also with nitric acid at 32% 

 exhibits neither effervescence nor disengagement of nitrous 



I fused this reddish calx of tin with three parts of black 

 flux and a little charcoal powder, and extracted from it 18 

 pounds of tin per quintal. This metal was brittle, a pro- 

 iperty arising from tlie lead, which contributes also to at- 

 ^tenuatc the colour of the tin. If the lead is found there iu 

 ti'. ^ larger 



