1814.] Scientific InteUigence. 313 



shall make a few observations, uhicli may perhaps be of service to 

 my corrtspondent. 



]. Suppose a piece of matter is presented to us, and we wish to 

 know whether it contain a notable quantity of black oxide of man- 

 ganese. 1, Reduce it to powder, and pour upon it muriatic acid; 

 then ap|)ly a moderate lieat. if chlorine Le disengaged in abun- 

 dance, your ore i- chiefly manganese. 2. Melt a little borax or 

 soda upon a thin plate of |)Idtiiium by the ijlow-pipe, add a little of 

 your ore, and keep it melted by the interior flame of the candle. 

 The colour will be at first red, but will gradually disappear if the 

 ore be manganese. Now add a little nitre, or keep it melted for 

 some time in the exterior flame, and the red colour will again 

 appear. 



2, The method of separating manganese from iron has been 

 explained in a preceding Number of the ylnnals of Philosopky. 

 The solution of pure manganese in acids is colourless ; it is precipi- 

 tated by alkalies white, but becomes speedily black when left upon 

 a filfer. This is the usual test of manganese employed by chemists, 

 and it is quite sufficient to distinguish this metal from all others. 

 Manganese is not precipitated from acids by bicarbonate of potash, 



VII. On the Degree of Cold ohta'med hy Professo?- Braun. 



An anonymous Correspondent from Ireland has put to me the 

 following question : — " In the Translation of Hatty's Natural Phi- 

 losophy by Dc. Olinthus Gregory, vol. i. p. 200, he says, (speaking 

 of Mr. Braun,) the mercury continued to descend, and arrived in 

 the last experiment at — 352° of Fahrenheit. Now 1 am uu- 

 villing to believe that the intensity of cold mentioned by Haiiy has 

 been ol)tairied. Your opinion on the subject I should consider as a 

 great favour." 



Haiiy's book was a hasty and imperfect performance, suddenly 

 written, and published by order of Bojia|)arte. Hence wc need 

 not be surprized at the numerous omissions so perceptible in it. 

 JJraun, in his original account of his expciimcnts, states the cold 

 to have been as intense as — 352°. He was deceived by this cir- 

 cumstance. When mercury freezes it contracts about -^xh part of 

 its volume. Braun supposed this contraction the consequence of 

 cold, whereas it was the consequence of the congelation of the 

 mercury. We cannot detennine any degree of cold below — 40' 

 by a mercurial tliermoineter. Therefore the cold obtained by 

 Braun remains unkn«)wn. His mistake was first pointed out and 

 explained by Mr. Cavendish. 



VHI. Iodine. 



In answer to the ohservatirms and inquiries of the same gentle- 

 man resi)ecting the preparation ot iddiiie, 1 may say that the yellow 

 precipitate is usually a compound of iofline and sulphur, and con- 

 stitutes the objection to the mode of obtaining iodine in the wav I 

 formerly incuiioned. 1 shall therefore take the liberty ol' giving 



