78 Intelligence and Miscellaneous Articles. 



4. Influence of the zinc. — Amalgamated zinc, as is known, gives 

 stronger batteries than non-amalgamated ones ; but the force varies 

 also notably with the state of the amalgam and the purity of the 

 zinc. Commercial zinc amalgamated four days, and presenting a 

 crystalline surface giving 18,796, I found only 18,510 for pure 

 distilled zinc dissolved in pure mercury ; difference, 286. 



5. Influence of the purity of the sulphuric acid. — Ordinary commer- 

 cial acids contain traces of nitrogen compounds which increase the 

 electromotive force of Smee's battery. Thus with an ordinary acid 

 I obtained 18,961 instead of 18,796 as with a pure acid; difference, 

 165. 



6. Influence of the water. — The influence of the water is to me the 

 most inexplicable. While with distilled water I obtain the normal 

 number 18,796, with unfiltered Paris water it was only 16,886; 

 difference, 1910. 



7. Influence of the temperature. — The influence of temperature on 

 the conductibility of saline solutions and of metals is too marked 

 not to be shown, if not upon the electromotive force of a pile, at 

 least on its numerical estimation. Exact results are not possible if 

 the temperature of the circuit varies in any of its points during the 

 course of an experiment ; no comparable results are obtained if these 

 results of the variation of conductibility, due to the changes of tem- 

 perature from one experiment to another, are not corrected. 



In fine, to have concordant results, I work with a Smee's battery 

 consisting of a plate of platinized platinum immersed vertically in a 

 mixture of sulphuric acid with eight or ten times its weight of 

 distilled water boiled free from air. This solution is in a vertical 

 glass tube, at the bottom of which is a liquid amalgam of pure zinc 

 dissolved in pure mercury. A platinum wire traversing the bottom 

 of the tube forms the negative pole of the element. The element is 

 immersed in a large vessel fall of water, which keeps its temperature 

 constant ; by this arrangement the traces of sulphate formed arrive 

 with difficulty at the platinum : the liquids, moreover, are frequently 

 changed. Porous vessels are a source of trouble. Instead of varying 

 the resistances so as to cause the intensity of the current to oscillate 

 between two constant limits, and measuring by means of the rheostat, 

 according to Wheatstone's method, the variable resistance employed, 

 I introduce in the circuit fixed resistances in platinum, the tempera- 

 ture of which is exactly known, and hence the resistance determined ; 

 and I measure the corresponding variable intensities. 



I take 18,510 for the electromotive force of this pile, which regu- 

 lates the value of my constant coefficient. — Comptes Rendus, Novem- 

 ber 4, 1861. 



EXAMINATION OF THE WINDOW-GLASS OF POMPEII. 

 BY M. G. BONTEMPS. 



After citing the few references to window-glass to be found in 

 ancient authors > and adverting to the dispute which has prevailed 

 as to the antiquity of the invention of that material, the author quotes 



