74 Scientific Intelligence. [Jan. 



Article XI. 



SCIENTIFIC INTELLIGENCE, AND NOTICES OF SUBJECTS 

 CONNECTED WITH SCIENCE. 



I. On the Temperature produced by the Condensation of Vapour. 



Mr. Farada}', in some observations published in the Annales de Chi- 

 mie, xx. 329, has illustrated a curious property of vapour which, as 

 he remarks, . though it might have been deduced from known facts, 

 had never been cited or confirmed by experiment. It seems, indeed, 

 that the property had been known in Paris to some of the chemists, 

 but that it had never been published. . 



Hold a thermometer horizontally so that its bulb may be introduced 

 into a current of vapour as it issues from a boiler or tea-kettle: it will 

 soon indicate 212° ; then drop on to it a little powdered nitre, and 

 immediately the temperature will rise to 230° or higher. This effect 

 is due to the condensing power excited by the salt on the vapour, 

 which, reducing the latter to the fluid form, liberates the heat that 

 raises the thermometer. 



In making the experiment, care should be taken that the water con- 

 densed on the stem of the instrument does not run down and dilute the 

 salt, for then the temperature foils. Another method of operating is 

 to tie up the salt or substance, round the bulb of the thermometer 

 in a bit of lint or flannel, and introduce it so covered into the steam. 

 The following are temperatures obtained by the use of different sub- 

 stances ; the first column of numbers as given by the last process, and 

 the second by the other : 



Sulphate ofmagnesia 214 .... 218 



♦Tartrate of potash 2?0 236 



*Tartaric acid 221 226 



Sugar 223 216 



•Muriate of ammonia 227 230 



♦Citric acid 228 230 



*Nitre 230 232 



Nitrate of magnesia 236 .... 236 



Nitrate of ammonia 240 .... 236 



Acetate of potash 258 .... 244 



Subcarbonate of potash 262 .... 258 



Potash — .... 300 and upwards. 



Those marked * are convenient for the experiment with the naked 

 bulb. 



The effect, as might be expected, continues at different pressures, 

 and the same difference of temperature which exists between a clean 

 thermometer and one coated with a salt when placed in steam at 212° 

 under atmospheric pressure, holds when the pressure and temperature 

 are raised. 



Mr. Faraday had stated that at the same pressure a bailing aqueous 

 saline solution gave off steam of the same temperature as boiling water. 

 M. Gay-Lussac makes some remarks on this statement, and shows, that 



