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IX. — On certain Obstructions which form in Draininr/ -Tiles. 

 By M. Hekv^ Maxgox.* Translated from an article in the 

 French Scientific Review, the ' Cosmos.' By J. EvELYN 

 Denisox, M.P. 



In certain soils the water from drains forms, more or less quickly, 

 a deposit of solid matters which create an obstruction in tiles, 

 prevent all flow, and render the work done useless. This is 

 the most serious mischief which can happen to works of drainage ; 

 and unless it can be prevented, it is vain to attempt the improve- 

 ment of lands liable to be so affected, bv draining. The ob- 

 structions formed in tiles by the chemical deposit of substances 

 held in solution in tfie drainage-water are of two different natures. 

 One is formed principally of carbonate of lime ; the other con- 

 tains a large proportion of oxide of iron, and exhibits an ochreous 

 colouring, which has acquired for it the name of the ferruginous 

 deposit. 



1 will now explain the results of my investigations into these 

 two classes of obstructions, and the simple means by which I am 

 enabled to prevent their formation in draining-tiles. 



Calcareous Obstructions. — Spring waters in calcareous soils 

 contain sometimes a sufficient proportion of carbonate of lime to 

 form incrustations ; that is, they will deposit by exposure to air a 

 greater or less proportion of calcareous salts. The same phe- 

 nomenon occurs in draining-tiles ; the bore rapidly diminishes, 

 soon it becomes Insufficient to allow a passage for the water 

 which should How througli them, and the fruits of a great 

 outlay are entirely lost. Waters charged with carbonate of lime 

 hold it in solution by means of the carbonic acid gas which 

 they contain. They remain limpid as long as the gas does 

 not disengage itself. The calcareous deposit is only formed 

 when the quantity of carbonic acid is no longer proporlioncd to 

 the calcareous salt which the water contains. The lormation ol 

 calcareous substances in drains may therefore be obviated by 

 preventing the disengagement of the carbonic acid in the water 

 which runs in tlie tlrains. This is easilv done by cutting off all 

 communitation between the drains and the external air. The 

 small (piaiitity of atiiiosj)heric air in the subterraneous conduits 

 soon imbibes carbonic a»id in proportion to the volume of gas 

 dissolved in the water, Tliis has then no longer a tendency to 

 disengage its(;lf. The water charged with the calcareous matter 

 preserves its limpiditv, and the flow may continue without inter- 

 ruj)tion. Xothiug is more easy than to realise this in jiractice. 

 It is only necessary to place an air-trap (un regard pneumatique) 



* M. Maii;'oii's papiT was rvail at the Iiistitiit Imperial de Frain-i', Aoademic dcs 

 Sciences, and received with Bpprobalion, at the sitting of AitgMSt 25, 1856. 



