ON SPARRY IRON ORIS. 315 



ntari)' two years ago in the Philosophical Journal ; but their 

 ::>ileiice obliges me to become my own accuser. Jiome expe- 

 riment of mine will be found in your number for JVJarch, Water may be 

 1806', from which I inferred, that water cannot retain its go© 

 fluidity when cooled below 32°. Such was my opinion at 

 the time, but I was soon induced to suspect its accuracy from 

 a conversation on the subject with Mr. Dalton, of Manches- 

 ter. The gla&s vessels Ubed in my experiment:* were exter* 

 nally covered, witb the freezing mixture nearly to their 

 brims; but in consequence of this gentleman's infownation, 

 I repeated the same experiment last winter, care being taken 

 to raise the upper half of the vessel, containing the water, above 

 the salt and snow which surrounded its bottom. With this 

 precaution I found water might easily be cooled many de- 

 grees beiow the freezing point ; in consequence of which dis- 

 covery, I was obliged to abandon the theory referred to above, 

 and HI pronouncing it to beanerrourlamonly doing justice to 

 the truth and your excjrllent miscellany. 



XIV. 



Report made to the Mathematical and Physical Class of the 

 Institute, on a Memoir of Mr. Descotils, relative to Iron 

 Spar: hy Messrs, Berthollet, Lelietre, and Vav- 



QUELIN*. 



spara vary 



JLN January 1806 Mr. Descotils read to the class a memoir iron 



in wbich he proved by expenmer\t8, that the iron spar, which ^"^ *heir princi- 



was the subject of it, varied in the proportions of its consti- be differently 



tuent principles ; and hence he explained the differences treated. 



that the ores require in their metallurgic treatment. The 



difficulty of fusing some of them constituted at that time 



the principal object of his research; and the comparative Their refracto- 



analysis he made led him to the conclusion, that the mag- '■'"^ss owing to, 



nesia, which is frequently found in them in large quantity, 



was the cause of their refractoriness. 



Reflecting on the processes adopted to deprive these ores Processes Tsy 



•j^nales de Chimie, vol. LXIJ, p. 135^ May, 1807. 



of 



