260 report — 1859. 



positive molecules predominate ; acidity when the electro-negative are in excess. 

 By writing minus points to show the want of symmetry, it is possible to indicate a 

 priori whether an acid is monobasic, bibasic, or tribasic. In conclusion, the author 

 referred to the oxides of nitrogen, chlorine, and carbon as illustrations of the import- 

 ance of symmetry. Writing them all on four-volume formulae, it is necessary to 

 double them when the compound has an uneven number of molecules of oxygen ; 

 but the oxides of an even number do not require this duplication. Further, it was 

 shown that the symmetrical oxides are neutral or only feebly acid in character in the 

 case of the oxides of electro-negative elements. Thus hypochlorous, chlorous and 

 chloric acids are uneven, like nitrous and nitric acids ; while binoxide of nitrogen 

 and the peroxides of chlorine and nitrogen are neutral from there being a balance in 

 the molecules of oxygen. In like manner oxalic acid, with an uneven number of 

 atoms of oxygen, is more powerfully acid than carbonic acid, where the conditions 

 for symmetry are more nearly satisfied. 



On two new Photochemical Experiments. By M. Nikpce de St. Victor. 



1st Experiment. — Chemical Photometer. Into a flask with a neck is introduced 

 a solution of oxalic acid so concentrated that a portion of the salt remains undis- 

 solved at the bottom ; into this solution a certain quantity of a solution of nitrate of 

 uranium, or simply of oxide of uranium, is next poured ; the flask is then hermetically 

 sealed by a cork, through which passes a straight, graduated tube, whose lower ex- 

 tremity reaches below the surface of the lquid, and whose upper one rises to a certain 

 height above the cork. The apparatus being thus constructed, no particular phe- 

 nomenon manifests itself so long as the bottle remains in the dark; the liquid in the 

 tube remains at the same level as that in the flask : but when exposed to diffuse, or 

 to direct solar light, the oxalic acid, under the influence of light aided by the presence 

 of a salt of uranium, becomes decomposed and gives rise to the formation of carbonic 

 oxide, which latter, collecting in the flask and pressing on the surface of the liquid, 

 causes the same to rise in the tube with a rapidity and to a height proportional to 

 the chemical intensity of the light. The little apparatus is in fact a chemical photo- 

 meter, and acts admirably ; it remains to be seen whether the proportionality between 

 disengagement of gas and chemical intensity is constant, and whether by this means 

 it would be possible to measure accurately the chemical action of diffuse or solar light 

 at different elevations of the sun, at various seasons and at different places ; whether, 

 in short, the mixture of M. Niepce de St. Victor is capable of completely replacing 

 the gaseous sensitive mixture of Bunsen and Roscoe. We earnestly recommend this 

 new kind of experiment to M. Poey, who resides in the favourable climate of Havanna. 

 The magnitude of the tube's diameter and the best method of graduation also remain 

 to be determined. 



2nd Experiment. — Photochemical Pile. In this experiment a flask is chosen with 

 a wide neck through which two plates may be passed, one of zinc and the other of 

 copper ; to these plates two copper wires are fixed so as to form a small element 

 of a simple pile. The liquid, or rather the mixture of liquids poured into the flask, 

 is the same as in the preceding apparatus, viz. a solution of oxalic acid with an 

 excess of salt and a solution of oxide or of nitrate of uranium. When the circuit is 

 closed, even in the dark, an action at once commences, and a current is produced 

 capable of deflecting the needle of a sensitive galvanometer. But when the flask is 

 exposed to the light the action becomes incomparably more energetic, the quantity 

 of carbonic oxide formed is very considerable, its disengagement in the form of smoke 

 or transparent cloud is visible to the eye. To a certain degree the oxide or nitrate of 

 uranium may be replaced by nitrate or perchloride of iron. 



Geology. 



On the Discovery of Silurian Fossils in the Slates of Downshire. 

 By James Bryce, M.A, LL.D., F.G.S. 



In a paper laid before the Geological Section of the Association at the Belfast 

 Meeting in 1852, the author has described the structure of these slates and their 



