as deduced hy himself and Dr. Suerman. 341 



order to their being comparable with mine, be multiplied by 



P 

 The apparatus employed by Suerman was one of a very 



ingenious but rather complicated description, and, as an exact 

 idea of all its parts cannot be well conveyed without a dia- 

 gram, for a detailed account of it I must refer to his own 

 essay. The general principle, however, on which it acted is 

 easily explained. Tlie air or gas which was the subject of 

 experiment was, under the pressure of a column of water 

 which was maintained constant by the well-known contrivance 

 of Marriotte, forced from a gasometer through oil of vitriol 

 contained in an adjacent Wolfe's bottle, and thence through 

 a tube packed with fragments of fused chloride of calcium. 

 Escaping from the tube in a state of desiccation, it was next 

 made to enter one of sheet tin, through the sides of which were 

 inserted a manometer, to show the interior pressure, and a 

 wet and dry thermometer ; and having traversed this it passed 

 on to a second gasometer, from whence it was made by the 

 same means, if necessary, to return to its original reservoir, 

 flowing in succession through the oil of vitriol, the chloride 

 of calcium, and the calorimeter or tube containing the mano- 

 meter and thermometers. In the experiments on atmospheric 

 air, the pressure of water was employed ; but the other gases, 

 lest they should become contaminated by the air with which 

 water is naturally impregnated, were impelled through the 

 apparatus by the hydrostatic pressure of a saturated solution 

 of common salt, which was selected on account of the very 

 small amount of air which it is capable of absorbing. From 

 the sketch given of the apparatus (p. 270) the reader will have 

 perceived that when the air or gas has been forced from gaso- 

 meter A into gasometer B, it is possible to continue the 

 current with scarcely any interruption, and cause it to return 

 from B to A, passing of course in both cases in a state of 

 perfect dryness through the tube containing the thermometers. 

 It being, however, difficult to render the second current per- 

 fectly continuous, and identical in velocity with the first, 

 Suerman completed his experiment in every instance while 

 the elastic fluid was passing from A to B, by resorting to the 

 simple expedient of cooling the wet thermometer before its 

 introduction into the apparatus, by means of which the sta- 

 tionary temperature was attained long before the contents of 

 gasometer A had been expelled. To this description it is only 

 necessary to add, that, by the proper management of a stop- 

 cock placed at the extremity of the tube containing the ther- 

 mometers, he was enabled so to regulate the blast during each 



