138 Tr^ubia Vol . Ill, Z 



Plan No. 4 indicates the arrangement of the cellar, which is nothing 

 else than a reinforced concrete box entirely closed, whose floor carries a 

 number of reinforced concrete walls, 1.30 M. high, which divide the 

 cellar into reservoirs, filter tanks and accomodation ways. 



The sides of the square base of the filter tanks are 3,30 M, long 

 in the clear, and the height of the tanks 1,30 M. clear, the contents of 

 each tank is, consequently, fully 14 cubic Metres. 



The filter tanks, through which the water percolates from top to 

 bottom (submerged filters), are filled in the reverse order with two layers 

 of bricks laid loosely, one layer of road metal 8 cm. thick, approxima- 

 tely, one layer of gravel from 2 cm. to 5 cm. diameter, 20 cm. thick, and 

 last of all a layer of clean quartz sand, 60 cm. thick. 



This quartz sand is procured from Tandjong Ruh, in the Klabat Bay, 

 on the island of Banka. 



Through the kind office of the Department of Tin Mining at Banka 

 (Dienst der Banka Tinwinning) and also of the Department of Navigation 

 (Dienst van Scheepvaart), 1 managed to get 40 cubic Metres of this sand 

 transported to the Laboratory site at Batavia. 



The top of the quartz sand layer lies about 15 cm. below the top 

 edge of the filter tanks. 



Each of the two filter tanks is able to treat the whole of the circu- 

 lating water rapidly enough by itself, and the need for this can arise 

 when one of the filter tanks is thrown out of action in order to clean 

 it; normally, however, the water from the aquarium tanks is divided over 

 the two filters. 



The water that flows out from underneath the filters, comes into the 

 mixing reservoir (2, Plan No. 4) via the channel A or the duct a (see 

 Plan No. 4) in the manner indicated below. 



This mixing reservoir is precisely the same size as the filter tanks, 

 that is to say 3.30 M. by 3.30 M., by 1.30 M„ capacity 14 cubic Metres. 



Above this mixing reservoir is the distilled water reservoir (4, Plan 

 No. 3). From the latter reservoir distilled water can be added to the 

 seawater in the mixing reservoir by means of a short hard phosphor 

 bronze pipe fitted with a cock, which passes through the reinforced 

 concrete roof of the aquarium cellar. 



Below in the cellar, this pipe is coupled to a thick rubber hose 

 with a hard rubber (= ebonite) cock on its end. 



It is possible to determine the amount of distilled water to be added 

 every day from an evaporimeter connected above each of the two -rows 

 of tanks, while a check on these additions can be effected by ascertaining 

 the salinity of the aquarium water at regular intervals. 



The water from the mixing reservoir flows through duct B (Plan 

 No. 4) to the Easterly end of the first large Southerly reservoir (3, Pian 

 No. 4). 



