NATIONAL LCADEMY OF SCIENCES. 



larger leg being about half an inch and the smaller about one- 

 tenth of an inch in diameter. Mercury is poured into the larger 

 and dilute sulphuric acid into the smaller tube, the latter liquid 

 resting on the former. On connecting the mercury with the 

 negative terminal of a voltaic battery and the acid with the positive 

 the mercury falls in the tube. Reverse the battery-terminals and 

 the mercury column rises. Moreover, Dr. Draper observes that all 

 these changes in position are accompanied by certain definite changes 

 of figure of the bounding surface, and shows that this might have 

 been expected from the theory of Laplace. Placing a globule of 

 mercury in acidulated water in contact with the negative terminal 

 of the battery he found that whenever contact of the positive termi- 

 nal was made with the acid an instant deformation of figure took 

 place, the upper surface being flattened, so that the mercury touched 

 the inclosing tube all around in a complete ring. This memoir, 

 published in 18o4, must be considered in all respects a remarkable 

 one, and anticipates clearly many of the more important later dis- 

 coveries. 



The phenomenon of osmose described by Dutrochet in 1827 had 

 been noticed by Dr. Diaper in the above memoir. A few years 

 later Dr. J. K. Mitchell had published a valuable paper on the 

 osmotic phenomena observed in membranes of caoutchouc. When 

 Dr. Draper entered upon his medical studies in Philadelphia, there- 

 fore, it was natural that he should take a lively interest in the phe- 

 nomena referred to, and particularly in their physiological relations. 



His experiments on gaseous osmose were original and important 

 and were baaed on the simple assumption that any substance in 

 contact with any other tends to diffuse into it. He found that am- 

 monia gas penetrated almost instantly films of shellac, gold leaf 

 and mica, and especially liquid films, whether these were thin, as in 

 a soap bubble, or were composed of a layer of water of quite con- 

 siderable thickness. When such a layer separated carbonic-acid 



and hydrogen gases, for example, he observed that the phenomenon 



was a simple one and consisted in the mutual solution of the gases 

 in the liquid, their transference through the film, and their subse- 

 quent evaporation, the process ceasing when the at niosphere on both 

 sides of the layer was the same. Using then a membrane of caout- 

 chouc he sought to discover whether gaseous osmose could be pre- 

 vented by pressure ; and he experimentally proved that sulphur- 

 ous acid passed into air under a pressure of 7 ' h atmospheres, car- 



