On the Stopjjage of Drains hy a Stony Dej)osit. 121 



From Mr. Way. 



" I send you the analysis of the water and the deposit : you will 

 readily observe that the composition of the water sufficiently 

 accounts for the deposit, which indeed it closely resembles in 

 character. The quantity of carbonate of lime in the water is not 

 however excessive^ and it must require some time to form so large 

 an accumulation. From the analysis it is quite clear that the 

 drains are stopped, not mechanically, but by a chemical precipi- 

 tate ; this is evident by simple inspection of the substance : the 

 deposit is principally carbonate of lime, and I believe the pheno- 

 mena you mention may be referable to the following causes : 

 the stone drain would probably for the most part be only 

 partly filled with water, and would leave opportunity for the 

 escape of the carbonic acid, by which the carbonate of lime is 

 held in solution ; the result being a crystalline deposit of this 

 substance, which in time would choke the drain. I must add 

 that the stone acts like a piece of bread in a glass of champagne, 

 in affording points for the escape of the gas. 



"' In the turf-drains, on the other hand, there would most likely 

 be a gradual evolution of this gas from decomposition of vegetable 

 matter, and the water, remaining fully charged with carbonic 

 acid, would not afford a deposit, or, if at all, in smaller amount. 

 From the small size of turf or wedge-drains, 1 can quite under- 

 stand that they would not be filled up, because they must contain 

 less air for the carbonic acid to escape into, and fewer points of 

 escape for it even were other circumstances favourable. 



^' Analysis of a deposit taken from a stone drain :-— 



" Carbonate of lime 86-38 



Sulphate of lime . . • 2-52 



Magnesia, common salt traces. 



Insoluble matter, sand, clay, &c 10*22 



99-12 



" N.B. — The sand and clay are deposited mechanically in thin 

 layers, obvious to the eye, between the thicknesses of carbonate of 

 lime. 



" Analysis of the water passing through the drains : — 

 " Solid matter in a pint of the water 3*160 grains, consisting of— 



" Carbonate of Hme 2-123 



Sulphate of lime 0*270 



Magnesia 0-058 



Common salt 0-216 



Silica 0-338 



Vegetable matter 0*154 



3-160" 

 ^'T. Thomas Way." 



