MODIFIED by COMPRESSION. 135 



no longer exifts, having crumbled entirely to pieces, notwith- 

 ftanding all the care I took to inclofe it with glafs and wax. 



April 26. - An experiment was made with fome .carbonate 

 of lime, purified by my friend Sir George Mackenzie. Two 

 grains of water were introduced, but were loft, I fufpecT:, as in 

 the laft cafe. The heat applied was 32°. The lofs of weight 

 was 10.6 per cent. Yet, though made but one day after the 

 laft-mentioned fpecimen, it remains as frefh and entire as 

 at firft, and promifes to continue unchanged. The external 

 furface, as feen on removing the lid of the conical cup, was 

 found to mine all over like glafs, except round the edges, 

 which were fringed with a feries of white and rough fphericles, 

 one fet of which advanced, at one fpot, near to the centre. 

 The mining furface was compofed of planes, which formed ob- 

 tufe angles together, and had their furface ftriated ; the llriae 

 bearing every appearance of a cryftalline arrangement. When 

 freed from the cup, as before, the fubftance moulded on the 

 platina was found to have aflumed a fine pearly furface. Some 

 large air-bubbles appeared, which had adhered to the cup, 

 and were laid open by its removal, whofe internal furface had 

 a beautiful luftre, and was full of ftrise like the outward fur- 

 face. The mafs is remarkable for femitranfparency, as feen 

 particularly where the air-bubbles diminifh its thicknefs : a 

 fmall part of the mafs being broken at one end, mews an in- 

 ternal faline ftru&ure. 



April 29. — A cup of platina was filled with feveral 

 large pieces of a periwinkle * (hell, the fharp point of the 

 fpiral being made to ftand upright in the cup, (fig. 30.). A 

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

 carbonate loft no lefs than 16 per cent. The fhell, particularly 



the 



* Turbo terebra, Lin. 



