Pneumatics — Mineralogy. 367 



PNEUMATICS. 



3. On the cold produced hy the dilatation of air. By M. Legrand. — 



The general law that air is cooled by its dilatation was controverted by 



MM. Gay-Lussac and Welter, in the particular case where it is blown 



out of an aperture under a constant pressure- This strange result, which 



was deduced from an experiment made with a fire engine at Chaillot, is 



published in the Ann. de Chim, torn. xix. p. 416. M. Legrand, Professor 



of Natural Philosophy at Besanjon, has obtained very different results from 



the same engine. The following were his observations : — 



Distances from the aper- Temperature, ^ v 



tureorcock. Cent C°°^^°g- 



10 million. 22 7°.5 



50 25.5 4 



100 26.8 2.7 



200 28.8 0.7 



250 29 0.5 



The temperature of the external air was 29°.5, and the third column is the 

 difference between this number and the temperature in the second column. 

 When the cock was taken out altogether, and the bulb of the thermometer 

 put in its place, the temperature oscillated between 12°.5 and 13°.5, so that 

 the cooling was here aibont Jij'teen degrees centigrade, or twenty-seven de- 

 grees of Fahrenheit. 



The experiments were repeated in June 1829 by M. Saigey, who obtain- 

 ed analogous results. — Annales des Sciences d' Observation^ No. i. p. 45. 

 Par M. M. Saigey and Raspail. 



II. NATURAL HISTORY. 

 MINERALOGY. 



4. Analysis of the Brochantite. {Moh&'s Mineralogy, translated by Haid- 

 inger, vol. iii. p. 81.) — Mr Magnus of Berlin has found in the variety of 

 this ore from Transylvania, the specific gravity of which was = 3.78 ... 

 3.87, the following elements : — 



Oxide of copper, - - 66.935 



tin, - - 3.145 



lead, - - 1.048 



Sulphuric acid, - - 17.426 



Water, - - 11.917 



FoTmnUiCuSS + SAq 



Poggendorff 's Annalen, vol. xiv. p. 141» 



