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V. 



ON THE COMPOSITION OF TWO HAED-WATEE DEPOSITS. 

 By W. N. HAETLEY, F.E.S, Eoyal College of Science, Dublin. 



[Read December 17, 1890.] 



These two deposits, -wliicli have been formed from hard waters, 

 have some points of interest on account of their composition being 

 in certain respects very similar, though the waters came from 

 entirely different districts. 



No. 1. — This deposit was formed inside a service-pipe which 

 conveyed water across " The Meadows " to a distillery on the south 

 side of Edinburgh. It was presented to me about ten years ago 

 by Dr. Little John, the medical officer of health for that city. The 

 internal diameter of the pipe was 6 inches. At first the supply of 

 water was ample, but after some time it began to decrease, and at 

 last was found to be insufficient ; but this was not the fault of the 

 well, which contained plenty of water. On breaking open a pipe, 

 it was seen that a stony deposit, 1^ inches in thickness, had 

 reduced the bore from 6 inches to 3 inches. 



The deposit is yellowish-grey to greyish-yellow in colour. A 

 section of it shows a series of concentric rings of different varia- 

 tions in colours and varying thicknesses : the inner surface, that is 

 to say, next to the running water, and therefore the last deposited, 

 is somewhat slightly mammelated. 



Under the microscope it presents the appearance of an aggre- 

 gate of translucent yellowish crystals. 



Of course the chief feature in the chemical composition of the 

 deposit is the calcium carbonate, but that which is most note- 

 worthy is the large amount of organic matter, nearly 20 per 

 cent., which the dried deposit contains. 



