244 Producilon of Mxifialic Acid and Soda 



Hence the caase of that variation which obtains in the 

 apparent magnitnde of an object, is no longer a matter of 

 mere opinion; for it is an established law in dioptrics, that the 

 image in the focus of a convex lens increases with the aper- 

 ture of the gla'^s, and consequently, the picture of the moon 

 in the focus of the cvystalline lens of the eye increases as the 

 pupil is enlarged. I am, sir, 



Your btimble servant, 



Ez. Walker. 



XLIV. Extract of a Letter from M. Leopold de Buck, 

 of Milan, to Professor Pictet, of Genei'a, on the Pro- 

 duction of Muriatic Acid and Soda hy the Galvanic De- 

 composition of' IVater *. 



SIR Milan, October 6, 1 805. 



X HAVE a few words to say on the snbjcct of a fact which 

 at present occupies the attention of the Italian philosophers, 

 and particularly Volla. It is the experiment whereby we 

 compose the muriatic acid and soda by means of the Gal- 

 vanic action. We have been told that this experiment, for 

 which we are indebted to Dr. Pacchiani, has not succeeded 

 at Geneva f. The following is the method to make it suc- 

 ceed at all times : 



Have two piles, the one near the other, and joined to- 

 gether at the base, in such a manner, that the positive pole 

 of the one and the negative pole of the other shall be at the 

 superior extremities of the two piles. Conduct a gold or 

 platina w^lre from the negative pole (of zinc) into a tube A, 

 slightly closed at the top by a piece of linen or a cork, 

 through which the wire passes in descending down about 

 two-thirds of the tube. Make another wire of the same 

 substance also descend from the positive pole (of copper) 

 into a tube B, disposed in the same manner as the preceding. 

 Plunge both of them into a drinking-glass containing di- 

 stilled water. Oxygen will be disengaged in the tube B, and 



• From Bihliothefjue Bnta'miquc, vol. xxx. 



^ We do not believe it was ever tried at Geneva.— Pictet. 



hydrogen 



