426 Mkcell ft neons Ifdelligence. 



ii. Chkmicaf. Science. 



§ 1. Chemistry. 



1. On the Chemical Phenomena of thin Plates. — Sig. A. Fusit 

 nieri has inserted an account of a long series of experiments on tlie 

 chemical action which takes place in very thin layers of various 

 substances. The fixed and volatile oils, alcohol, ether, balsams, 

 Sfc. were placed on glass, water, and mercury, in the air, i/i. 

 vacuo, in different gases, and in different positions, and the pheno- 

 mena, carefully observed. These are detailed in the Giornale di 

 Fisica, iv. pp. 133, 209, 287, and are to be continued ; but the 

 following are the general principles deduced from the three first 

 parts of the memoir. 



1. All liquid substances reduced to uniform laminte, so thin as 

 to decompose light by reflection and transmission, have the 

 power of throwing off their own substance in the direction of 

 the angle of the wedge parallel to the plane, which passes by the 

 angle perpendicularly to the thickness. 



2. This expulsive force is in the same substance always less as 

 the wedge is more acute, and greater as the wedge is less acute, 

 within certain limits not yet determined. 



3. From this force proceeds the spontaneous expansion of li- 

 quid masses reduced in some parts to thin cuneiform plates, and 

 continued in that direction (1), if the movement be not impeded 

 by external obstacles. In this way drops which form themselves 

 into spherical segments on horizontal surfaces that have no attrac- 

 tion for the drops, and admit of free motion, expand in all direc- 

 tions. 



4. If the expansion is impeded, not by external obstacles 

 placed in the line of its direction, but by some other force which 

 obliges the wedge-shaped lamina to preserve its form, then, by 

 the action of the same force, the substance is successively with- 

 drawn, and extended in the same direction. 



5. When the obstacles to the motion are opposed to the angle 

 of the wedge, then the force re-acts in a direction normal to the 

 resistance, and therefore nearest to the primitive direction, pro- 

 ducing expansion in the new direction. 



6. This force of expansion is smallest in water and aqueous 

 solutions, much greater in all combustible liquids, and among 

 these greater with the odorous than the inodorous substances. It is 

 "reate^t of all in the odorous and volatile substances. In the sul- 

 phuric and nitric acid it exists in a degree equal to that of the 

 volatile combustible liquids. 



7. The vapours which arise from the laminae of volatile liquid 

 combustibles, if retained in contact with their respective sub- 

 stances, impede the expansion of re-action in the direction normal 

 to the plane of the lamina (5). 



