190 Mr. Warington on Alteration of Carbonate-of-Lime [Dec. 5j 



intervals during a long peripd of time. And inasmuch, as the degrees of 

 hardness, indicated by the measures of Clark's soap-test, presented a very- 

 ready, accurate, and simple means of arriving at this result, that mode of 

 estimation was adopted, care being taken to displace any uncombined car- 

 bonic acid by agitating the sample with atmospheric air prior to the addition 

 of the test, as directed by Dr. Clark, the indications or degrees thus ob- 

 tained representing the quantity of lime-salts contained in an imperial gallon 

 of the sample (70-000 grains of distilled water) in terms of carbonate of 

 lime. 



In order that the nature of the experiment may be more clearly under- 

 stood, it will perhaps be better for me, before stating the results thus 

 obtained, to describe briefly the construction and arrangement of the 

 aquarium, its position, and its contents. The tank consisted of a rectan- 

 gular zinc framing, twenty inches long by thirteen broad, and twenty-one 

 in depth, having slate cemented into it at the bottom and sides, and being 

 glazed at the back and front. It was filled with water to the height of 

 twelve inches, or a volume equal to ten gallons, and on the slate sides were 

 cemented, at the water-line, ledges of rockwork composed of sandstone and 

 tufaceous limestone from Matlock, on which were planted a few ferns, 

 chiefly Trichomanes, for ornament. The bottom of the tank was covered, 

 for about two inches, with a mixture of sandy loam and gravel, into which 

 several plants of the Vallisneria spiralis, the vegetable member of the ar- 

 rangement, were inserted. Some large fragments of rough rockwork, 

 principally limestone, v/ere also placed upright on the bottom to break up 

 the stiff outline of the square framing, and give a pleasing effect to the eye. 

 The animal branch of the circle consisted of four small crucian carp with a 

 gold carp. Several freshwater mollusks, principally Flanorhis corneus 

 and Limneus palustris, were also introduced to act as scavengers and con- 

 sume the decaying vegetation. The tank was loosely covered with a plate 

 of glass, so as to allow of a free admission of the external air, and at the 

 same time keep out a great deal of the soot and dust of the London atmo- 

 sphere and impede the too rapid evaporation of the water. As the Tricho- 

 manes were stated to delight in shade, a thin muslin blind was placed over 

 the covering glass. 



The aquarium was located in a window-way having an eastern aspect, but, 

 being surrounded within a few yards by the high walls of adjoining houses, 

 the direct rays of the sun only reached it for about three hours in the 

 morning during the months of June and July. It was established in 

 January 18.51, and has not since been disturbed, except by occasional sup- 

 plies of distilled or rain-water, to replace the loss in volume arising from 

 evaporation. It had been my custom to v/eed out the excessive growth of 

 the Yallisneria during the summer, and also to remove some of the flaky de- 

 posit of calcareous matter from the surface of the glass nearest the light ; 

 but as I considered that such disturbances might interfere with the course 

 of the investigation, these operations were discontinued. 



