﻿Calcium Carbonate in Water. 961 



lower temperatures ; the solutions were tested at different 

 periods until a steady solubility value was reached. 



The manner o£ filtration at the boiling-point occasioned a 

 great deal o£ difficulty. Simple filtration through a double- 

 walled porcelain funnel, fitted with a hardened fluted filter- 

 paper, and heated without by a water-jacket, was first 

 attempted ; but no satisfactory results could be obtained. 

 Although the filtration was carried oat as rapidly as possible, 

 the amount of evaporation from the filtrate was necessarily 

 considerable, and farther, the solution exerted an appreciable, 

 solvent action on the funnel itself, as was found by testing 

 with solutions of prior known concentration, At the lower 

 temperature also, open filtration could not be employed, since 

 the short exposure of the solution during filtration to the 

 carbon dioxide of the atmosphere led to a remarkable increase 

 in the solubility value obtained, 



The method of upright filtration was therefore adopted. 

 The solution was drawn by suction from the first to the 

 second silica vessel through a tube of pure tin, in the shape 

 of an inverted U, one arm qf which was longer than the 

 other. The longer arm dipped info the solution, and wns 

 closed at the end by means of a double layer of hardened 

 filter-paper, protected on both sides by squares of muslin, 

 the whole being tied tightly to the tin tube by ineans of 

 linen thread upon a ruhher hand. The shorter arm was 

 fitted to the second vessel with a rubber Qork, through which 

 passed a silica tube leading to the pump. A glass flask, 

 immersed in ice-cold water, was interposed as a con- 

 denser to intercept water vapour coming over from the hot 

 filtrate. 



By this method, using a tube of one^inoh diameter, two 

 litres of solution could be filtered over in a quarter of an 

 hour. Loss of water from the filtrate by evaporation, and 

 exposure to the air during filtration, were both avoided, and 

 for a short time concordant results were obtained. After a 

 few experiments, however, the hot solution began to attack 

 the tin tube, and once the surface of this was worn away, 

 the action increased rapidly, In the case of experiments at 

 the boiling-point, the filtrate, instead of being clear, was 

 quite cloudy on concentration, and, when tested, showed a 

 decided trace of tin, 



The tin tnhe w<is therefore discarded for a similar tube of 

 silioa, and with this satisfactory results at 100° l\ were 

 obtained. At the lower temperatures no noticeable action 

 was exerted by the solution upon the tin tube, and this wfts 



Phil. Maq. S, G. Vol. 23, No, 13*. Jm? 1913, 3 R 



