391 



scientific value will be in future. The entire investigation will be 

 published in the course of the summer. 



It is necessary to remark here that the following experiments 

 were made solely upon the coarser variety of the stone, known as 

 Common or Bed Rock ; the finer portions, not yet submitted to che- 

 mical investigation, being called Liver Rock, most probably from the 

 closeness of its grain. 



The objects which I had chiefly in view in the course of the follow- 

 ing inquiry were, the exact chemical composition of the stone ; the 

 extent to which it contains other insoluble substances than silica ; the 

 amount of substances soluble in pure water, in water saturated with 

 carbonic acid, and in water containing the mineral acids. The ex- 

 tent to which the stone absorbs and retains water, was also object of 

 investigation, and the coaly matter which occurs at intervals in it 

 was analysed. 



The whole of the analyses were made by Mr Thomas Bloxam, the 

 assistant-chemist in the Laboratory of the Industrial Museum, who 

 spent much pains on the inquiry. From what follows it will be seen 

 that the Craigleith sandstone, as taken in cubes for building, is nearly 

 all silica, but that it contains in addition small portions of alumina, 

 lime, magnesia, iron, and, occasionally, a hitherto unsuspected ingre- 

 dient, oxide of cobalt, which Mr Bloxam has distinctly indicated. 

 In addition to those substances, black particles occur disseminated 

 even through the whitest and most solid portions of the stone, which 

 in the majority of cases appear to be coaly matter, but are some- 

 times in greater part carbonate of the protoxide of iron, coloured by 

 an admixture of coal. 



The condition in which those bodies occur in the stone is as im- 

 portant as their relative amount ; but it is not so easily ascertained. 

 Much of the silica is present in more or less perfect grains of quartz ; 

 a small portion occurs as the chief ingredient of scales of mica, and 

 also probably as felspar ; and according to Mr J. Napier of Partick, 

 Glasgow, a certain amount of the silica is in combination with alu- 

 mina as clay. Mr Napier experimented by reducing the stone to fine 

 powder, and washing it on a flannel filter, which retained the silica, 

 and allowed the clay to pass through. Proceeding in this manner, 

 and receiving on a weighed filter paper the muddy water which 

 passed through the flannel, Mr Bloxam found that 9-33 per cent, of 

 substance remained on the paper after drying at 212''. This may pro- 



