62 Intelligence and Miscella?ieous Articles. 



the instrument is intended for the measurement of very high tempe- 

 ratures. If, for example, the air at 0° has an elastic force of 300 

 millims., it will acquire at 500° an elastic force of 850 millims., which 

 only exceeds the external pressure by about 90 millims. 



When operating at high temperatures, by a peculiar arrangement 

 of the apparatus it is possible to avoid the danger of an alteration 

 of the form of the reservoir when there is only one temperature to 

 determine. But there is always a cause of uncertainty arising from 

 ignorance of the law of dilatation of the envelope, which may be of 

 platinum instead of glass, in particular in the case of an air-pyro- 

 meter ; but this cause never leads to very considerable errors, as 

 may be seen by experiments made up to 350° on air-thermometers 

 with a glass envelope. The errors may become more considerable, 

 and even rise to several degrees when the temperature exceeds 300 , 

 if, the dilatation of the envelope between 0° and 100° being un- 

 known, the apparent coefficient of dilatation be deduced from the 

 elastic forces which the gas presents from 0° to 100°. 



M. Regnault indicates, in concluding, the possibility of employing 

 with advantage a thermometer of mercurial vapour, in a great many 

 eases in which the experiments do not require very minute precision ; 

 that is to say, this instrument would be a pyrometer intended to 

 measure temperatures above that of the boiling-point of mercury. 

 The mercury ariving at ebullition drives the air completely out of 

 the apparatus, and the vapour of mercury, behaving now as a per- 

 manent gas, dilates so as to remain in equilibrium with the external 

 pressure. By means of a peculiar arrangement, it is possible to ex- 

 tract the mercury which has been condensed on the sides and deter- 

 mine its weight, after the apparatus has cooled down to the tempera- 

 ture of the surrounding medium. By means of a very simple formula, 

 and by admitting for mercurial vapour the same coefficient of dila- 

 tation as that of air, the temperature to which the apparatus has 

 been exposed may be determined. It is requisite only, in order to 

 avoid the oxidation of the mercury at the beginning of the experi- 

 ment, when the mercurial vapour has not yet driven the air out of 

 the apparatus, to place in the vessel a little oil of naphtha, which 

 first drives out the air and then is itself expelled by the mercurial 

 vapour. 



M. Regnault announces that he intends to execute some experi- 

 ments, by this method, at the porcelain manufactory of Sevres ; we 

 do not know whether he has realized his project ; the results, if he 

 has obtained any, are still unknown to us. 



VI 1 1. Intelligence and Miscellaneous Articles. 



NEW PROCESS FOR EXTRACTING SUGAR FROM THE SUGAR- 

 CANE. BY M. MELSENS. 



THE following account of the new and important method of ex- 

 tracting sugar from the sugar-cane, is abridged from the first of 

 two long articles recently published in the Courier de V Europe. 



