Foreign Literature and Science. 187 



tained, and by dissolving off the gum in tepid water, the 

 plate presents characters, which, viewed by a lens, are 

 very legible and beautiful. From this plate, by means of 

 common printing ink, true fac-similies of the original wri- 

 ting may be produced. 



Writing already dry, may be copied in the same way by 

 going over the letters with a pen dipped in a very weak so- 

 lution of gum, and then sprinkling it with powder, and pro- 

 ceeding as before, the only requisite precaution in this me- 

 tallo-graphic operation, is, that the metallic plate must be 

 of an even thickness, and that the surface on which the 

 characters are traced must be smooth. 



An. Vindustrie national. 



27. Mineral Waters. — A memoir of Professor J. Anglada of 

 Montpelier, relative to the disengagement of azotic gas from 

 sulphurous mineral waters, published in the Annals de 

 Chimie of October last, exhibits the following results : — 



1st. Those mineral waters, which, by the uniformity of 

 their volumes, at all seasons of the year, seem to depend 

 least upon the variations of the atmosphere, imbibe never- 

 theless a portion of atmospheric air, which is probably re- 

 newed by currents, the origin of which is unknown. 



2d. The oxigen of the air, which accompanies sulphurous 

 waters, combines with their sulphurous principles, while 

 the azote escapes in a state of purity. 



This disengagement of azote, and the presence of aglai- 

 rous matter, analogous to animal substance, are good indi- 

 cations of degenerated sulphurous waters. 



4th. This reaction of the air upon the sulphurous princi- 

 ple of mineral waters, is effected at all temperatures. 



5th. If the characteristic phenomenon of this reaction 

 (the disengagement of azote) cannot be asserted with res- 

 pect to all sulphurous waters, (which requires more exact 

 observations upon all the varieties of water) it is at least 

 acknowledged that it holds good in all sulphurous waters, 

 that contain an alkaline hydro-sulphate, (sulphuret?) 



6th. The determination of this cause, destructive of the 

 characteristic principle of sulphurous waters will often lead 

 to the adoption of means proper to render this decomposi- 

 tion less active, and consequently to give a certain fixity to 

 the dominant virtues of these waters. 



