BY COMPRESSION. 



117 



surface, as seen on i-emoving the lid of the conical cup, wvis 

 found to shine all over like glass, except round the edges, 

 which were fringed with a series of white and rough spheri- 

 cles, one set of which advanced, at one spot, near to the cen- 

 tre. The shining surface was composed of planes, whicfe 

 formed obtuse angles together, and had their surface striated j 

 the striae bearing every appearance of a crystalline arrangc- 

 inent. When freed from the cup, as before, the substance 

 moulded on the piatina was found to have assumed a fine 

 pea/. ly surface. Some large air bubbles appeared, which had 

 adhered to the cup, and were laid open by its removal, whose 

 intenial surface had a beautiful lustre, and was full of stria; 

 like the outward surface. The mass is remarkable for semi- 

 transparency, as seen particularly where the air-bubbles di- ' 

 minish its thickness: a small part of the mass being broken 

 atone end, shews an internal saline structure. 



April 29. — A cup of platma was filled with several a shell partly 

 large pieces of a periwinkle* shell, the sharp point of the ^"^^'i ^^■''^^^ 'i'*-^ 

 spiral being made to stand upright in the cup, (fig. 30.). A gure a^ 30"/ 

 heat of 30"^ was applied, and no water was introduced. The 

 carbonate lost no less than 16 per cent. The shell, jjarticu- 

 larly the sharp end of the periwinkle, retained its original 

 shape in a great measure, so as to be quite discernible ; but 

 the whole was glazed over with a truly vitreous lustre. This 

 glaze covered, at one place, a fragment of the shell which 

 had been originally loose, and had welded the two together. 

 All the angles are rounded by this vitrifaction ; the space 

 between the entire shell and the fragment being filled, and the 

 angles of their meeting rounded, with this shining substance. 

 The colour is a pale blue, contrasted, in the same little glass, 

 with a natural piece of periwinkle, which is of a reddish-yel- 

 low. One of the fragments had adhered to the lid, and had 

 been converted into a complete drop, of the size of a mustard- 

 seed. It is fixed on the wax (at b), along with the other 



pecimens of the experiment (fig. 32.). This result shews, 

 as yet, no sign of decay, notwithstanding so great a loss of 

 S^'^eight. 



The last experiment repeated on the same day^ and pre- R^'petitfon *:' 

 pared in the same manner, with large fragments of shell, and [^^g^^Xai^ 



the point of the periwinkle standing up in the cup. A fusion." 



heat 

 * Turbo terebPij Lin . 



