Effects of Heat modified by Gompression. 23 



changed. The external surface, as seen on removing the 

 lid of the conical cop, was found to shine all over like glass, 

 except round the edges, which were fringed with a series of 

 white and rough sphericles, one set of which advanced, at 

 one spot, near to the centre. The shining surface was com- 

 posed of planes, which formed obtuse angles together, and had 

 their surface striated, the strise bearing every appearance of 

 a crystalline arrangement. When freed from the cup, as be- 

 fore, the substance moulded on the platina was found to have 

 assumed a fine pearly surface. Some large air-bubbles ap- 

 peared, which had adhered to the cup, and were laid open 

 by its removal, whose internal surface had a beautiful lustre, 

 and was full of stride like the outward surface. The mass is 

 remarkable for semi-transparency, as seen particularly where 

 the air-bubbles diminish its thickness: a small part of the 

 mass being broken at one end, shows an internal saline 

 structure. 



April 29.— -A cup of platina was filled with several large 

 pieces of a periwinkle* shell, the sharp point of the spiral 

 being made to stand upright in the cup (fig. 30). A heat 

 of 30° was applied, and no water was introduced. The car- 

 bonate lost no less than 16 per cent. The shell, partieu- 

 lar4y 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 vitrification ; the <pace 

 between the entire shell and the fragment being filled, and 

 the angles of their meeting rounded, with this shining sub- 

 stance. The colour is a pale blue, contrasted, in the same 

 little glass, with a natural piece of periwinkle, which is of 

 a reddish yellow. 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 specimens of the experiment (fig. 32). This 

 result shows as yet no sign of decay, notwithstanding so 

 great a loss of weight. 



• Turbo tercbra Lion, 



B4 The 



