and Vegetable Life on Carbonate-of-Lime Waters. 147 
consisted of four small crucian carp with a gold carp. Several 
freshwater mollusks, principally Planorbis corneus and Limneus 
palustris, were also introduced to act as scavengers and consume 
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 atmosphere and impede the too rapid evaporation of the 
water. As the Trichomanes 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 1851, and has not since been 
disturbed, except by occasional supplies of distilled or rain-water, 
to replace the loss in volume arising from evaporation. It had 
been my custom to weed out the excessive growth of the Vallisneria 
during the summer, and also to remove some of the flaky deposit 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. 
The results that have been obtained from this investigation dur- 
ing the years 1861 and 1862 are as follows :— 
= degrees of hardness, or grains of lime- 
1861. March 13 .... 26°2 salts, per imperial gallon, in terms 
of carbonate of lime. 
33 33 
33 33 
33> 33 
33> 3 
33> 33 
33 33 
33 
1862. Jan. ~ Z 
33 33 
33 33 
33 93 
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33 33 
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The amount of calcareous matter dissolved will be seen to have 
steadily decreased during the spring and summer months, from 
its maximum in March 1861 and February 1862 to its minimum 
in July 1861 and August 1862, and then to have increased as 
steadily during the autumn and winter months, 
Part of this hardness, however, unquestionably arose from the 
presence in the water of other salts of lime besides the carbonate. 
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