302 British Association for the Advancement of Science. 



instruments are used two gauges of observation, — one to show 

 when the generator is filled with water by the pumps, and con-^ 

 sequently all the free carbonic acid forced into the receiver ; and 

 the other to determine the quantity of liquid acid in the receiver. 

 A table of the elastic force or tension of the gas, over the liquid 

 carbonic acid was shown for each ten degrees of the thermometer, 

 from 0° to 150^^. The following are some of the results : 



Degrees. Ita. per square inch. Atmospheres of 15 lbs. each. 



- - - 279.9 - - - 18.06- 

 10 - - - 300 - - - 20 



30 - - - 39S.1 - - - 26.54 

 32 - - - 413.4 - - - 27.56 

 50 - - - 520.05 - - - 34.67 

 100 - - - 934.8 - - - 62.32 

 150 - - - 1495.65 - - - 99.71 

 Mr. A. intends to examine the pressure at higher temperatures, 

 up to that of boiling water and above ; and he asserted his belief 

 that it may be profitably employed as an agent of motion, — a sub- 

 stitute for steam, — not directly, as had been already tried by Mr. 

 Brunei, — -but indirectly, and as a means to circulate or recipro- 

 cate other fluids. The solidification of the acid was shown, and 

 the freezing of pounds of mercury in a few minutes, by the cool- 

 ing influence which the solid acid exercises in passing again to 

 the gaseous state. 



Dr. T. Thomson communicated a paper on the foreign sub- 

 stances contained in Iron. These are carbon, manganese, silicon, 

 and phosphorus in very minute quantities. 



Prof. Johnston read a paper on some exceptions to the laio of 

 Isomorphistn, showing that substances crystallizing in the same 

 form were not always composed of the same formulas. 



Dr. R. D. Thomson and Mr. T. Richardson presented a com- 

 munication on the decoinposition produced by the action of Emul- 

 siii on Anii/gdalin. 



A paper was olfered by Mr. Exley, on Chemical combinations 

 pi^oduced in virtue of the presence of bodies which remain to con- 

 tinue the process. It has been observed, said Mr. E., that in ma- 

 ny instances, powerful chemical affinities have been brought into 

 activity by the presence of certain bodies which remain insulated. 

 This Berzelius attributes to a peculiar force, which he calls cata- 

 lytic force. Several reasons are adduced to show that this force is 



