hy Contact of Liquids with Powdered Silica Sfc. 309 



The apparatus is placed in a situation in which the tempera- 

 ture remains sufficiently uniform, and is entirely surrounded 

 by a movable screen of cardboard. 



In making an experiment, the powder and liquid were 

 placed near each other in a covered glass vessel in a sheltered 

 situation during a period of sixteen hours, in order to acquire 

 the same temperature. The liquid was then poured into A, 

 and the powder into B, the cup A placed in position beneath 

 with the thermometer immersed in the liquid, and the entire 

 arrangement allowed to stand a sufficient period of time, 

 usually about half an hour, for the solid and liquid to regain 

 the same temperature. The outer tube B was then raised so 

 as to allow the whole of the powder to fall slowly in a thin 

 annular stream into the liquid. The powder entirely sur- 

 rounded and covered the bulb to a height of one fourth of an 

 inch above its upper end. If the bulb was not sufficiently 

 covered by it, the changes of temperature were less owing to 

 the liquid above being less heated than the powder. The 

 liquid was not stirred in any instance. The act of pouring 

 the liquid into A caused a rise of temperature of about *03° C, 

 but that of pouring the silica into B had no apparent effect. 

 The maximum rise by contact of the powder and liquid 

 usually occurred in about three minutes. The powders em- 

 ployed were almost wholly different from those used by 

 M. Pouillet, and were such as would not oxidize, and had no 

 recognized chemical action upon the liquid : it is important 

 also to use powders which do not agglomerate or change by 

 use. 



Experiments. 

 Silica with various Liquids. 



In all the following experiments with silica, except those 

 otherwise indicated, the weight of silica employed was 100 

 grains, the volume of solution was 50 centim., and the pro- 

 portion of dissolved anhydrous substance was 10 per cent, by 

 weight of the water. 



The silica was thoroughly purified and ignited previous to 

 each experiment, and was kept in a covered glass vessel 

 during the cooling until it was used. The proportion of 

 cyanogen in the cyanide agreed with that of 100 per cent. 

 KCy; but by evaporating a solution of it to dryness with an 

 excess of sulphuric acid, the weight of sulphate obtained 

 indicated a mixture of 14*45 per cent. NaCy and 85*55 KCy. 



The following Table shows the results of the experiments 

 with silica. 



Phil Mag. S. 5. Vol. 37. Ho. 226. March 1894. Y 



