Mr. Nai'IEE on Sandstones used for Building. 315 



suspended several pieces of stone on the surface of distilled v?ater for 

 several days, agitating the water occasionally, and at the termination of the 

 experiment found a good quantity of sand particles had loosened from the 

 stone and fallen off, and the water afterwards contained a trace of 

 lime and magnesia, and was white by a clay being suspended in it. 

 Repeating this experiment with water containing carbonic acid, the dis- 

 integration of the stone was more, and so was the lime in the water, 

 but the magnesia was not perceptible : there was also clay present. I 

 then took a piece of dry stone, ground it fine in a mortar, and placed the 

 powder in water, the sand particles sunk rapidly to the bottom, while the 

 clay remained suspended, and by several washings and decantings the 

 sand and clay could be approximately separated ; but there being also 

 mixed up in the stone, a great quantity of mica in fine scales, part of 

 which floated with the clay, a perfect separation of sand and clay could 

 not be made in this way. I then took the finely ground stone and placed 

 it upon a stout piece of flannel cloth as a filter, and poured water over it 

 until the water passing through was clear ; by this means the clay was 

 easily separated, and the remaining powder when dried had no longer the 

 dusty appearance referred to, the quartz being transparent and mixed 

 with scales of mica ; and the dusty portion washed off and passed through 

 the filter is mostly all China clay, finding in this way that the clay is 

 often upwards of twenty per cent, of the weight of the stone ; I have no 

 doubt it may form an important part in the tear and wear of the stone. 

 I have as yet found no easy means of separating mechanically the mica 

 from the sand grains, and therefore cannot give their relative propor- 

 tion, but they are variable. 



Knowing that practical men consider that the best stones are generally 

 found at the lowest part of the stratum or seam, I conceived that stones 

 found at different depths might contain different quantities of clay, and 

 so lead to some data, but the few trials I had on this head did not give 

 any regularity in the variation, as in some quarries the greatest quantity 

 of clay was found in the stone at the bottom of the stratum, and in others 

 at the top part of the seam, as, for instance, in one quarry a piece 2 

 feet down gave 20 per cent, of clay, and a piece 8 feet down gave only 

 14-6 per cent, of clay ; while in another quarry not above half a mile 

 distant from that referred to, a piece 2 feet down gave 8'5 per cent, clay, 

 and a piece 8 feet down gave 20 per cent. clay. However, my experi- 

 ments upon this part of the inquiry have not extended beyond these two 

 trials. Another question suggested itself. 



In washing out the clay, were the lime, iron, and other binding ingredi- 

 ents in the stone also washed out? In answer to this I found that in 

 general a great quantity of the lime and iron were washed away, but ia 

 no case was the whole of either lime or iron washed out with the clay ; 

 the following analyses will give the general character of these washing.*, 

 taking the average composition of the stone before washing : — 



