•36 French National Institute. 



must be taken to free the must from a more or less consi- 

 derable quantitv of tartar or other acids, wliith is eftected 

 by means of lixiviated ashes. This operation constitutes 

 . the essence of M. Parmentier's discovery. 



To return to chemistry in general : ii will be recollected 

 that pome time aoo M. Morveau endeavoured to find an 

 instrument for measuring the highest degrees of heat, and 

 of which we have frc^m time to time given an account. In 

 the jiresent year M. Morveau read to the class a complete 

 history of the attempts previously made by chemists and 

 manut'actuiers on this sui/ject ; he has appreciaied the me- 

 thods resorted to bv Newton, Muschcnl)roec k, Mortimer, 

 and particularly VVedgwood, to whom he does nuire jus- 

 tice than has hitherto been done in France. He has even 

 given an account of the experiments on the dilalability of 

 the metals, made bv watch-makers and otbers v>uh a view 

 of constructing compensation pendulums: lastly, he' has 

 described an instrument of his own invention, sufficiently 

 de'icue for showing the minutest changes in length ot a 

 small metallic bar. In short, it is only such a bar, par- 

 ticularly when made of platina, that can be at once suffi- 

 cientlv dilatable and unalterable in the fire to be used as a 

 pyrometer; but the greatest difficulty is to place it on a 

 scale which does not dilate, — otherwise we could never as- 

 certain the variations. This is is what M. Morveau expects 

 to attain, and to which he continues to direct his attention. 



M. Gay Lussac has recentlv developed an elegant law of 

 general chemistry, on the proportion of metal which enters 

 into each metallic salt, and on that of theoxvacn necessary 

 for its oxidation. He has proved that the metal which precipi- 

 tates another metal IVom an acid solution, finds in the preci- 

 pitated metal all the oxygen necessary for beitig oxidated, and 

 dissolved in such aqiiantitv that the solution is neutralized 

 to the same decree. The (]uantity of oxygen remains there- 

 fore constant, whatever be the quant ty necessary of each 

 metal : the acid is therefore in each salt in proportion to 

 the oxyo^en of the oxide, and there must be so much the 

 nioreof each metal for saturatitiir, the less occasion this me- 

 tal has for oxvgen in order to be oxidated. This law gives 

 a very simple method of determining the composition of 

 all the metallic salts ; lor it is sufficient to be acquainted 

 with the proportion of the acid in a salt of any kind, in 

 order to know it in them all,' and a single analv-i' dis- 

 penses vvith all the rest. It is always pleasing to fi ;d an 

 increase of simple methods for attaining precision in 



the 



