6 Historical Sketch of Improvements in [July, 



chemistry, and, therefore, is not far out of place, while I am 

 treating of chemical apparatus. The method which I use, and 

 to which I have alluded in the Annals of PJrilosopIn/, vol. xiv. 

 p. 147, is simply this : I wash tjlie oxalate of lime till it is per- 

 fectly clean, and then dry it by exposure to the open air, or to a 

 heat not exceeding 212°. I then put it into a platinum crucible, 

 the weight of which 1 have previously determined. This crucible 

 I enclose in a common hessian or black-lead crucible, and 

 expose it to a white heat for half an hour in a good wind furnace. 

 I then take it out of the fire, and, when cold, weigh the platinum 

 crucible again. The additional weight of the crucible gives the 

 quantity of lime ; for a white heat converts oxalate of lime into 

 quicklime. On dissolving this residuary quicklime in acids, I 

 never find any quantity of charcoal sufficient to make any sen- 

 sible alteration in the result. 



The oxalate of lime may be considered as a compound of 



1 atom oxalic acid = 4*500 



1 .atom lime = 3-625 



8-125 



^595 29 



Hence the lime which it contains ought to be ^j^ , or — , of 



the weight of the oxalate of lime. By this method we obtain 

 results that approach the truth pretty nearly ; but they are not 

 absolutely to be depended on unless we could succeed in depriv- 

 ing the oxalate of lime of the whole of its water, which I find it 

 very difficult to do. I find it, therefore, easier, and much more 

 accurate, to convert the oxalate of lime into quicklime. 



II. Light, 



1. Magnetising Properfi/ of the Violet Rai/.— The readers of 

 the Annals of F/ii/osophi/iiie aware of the experiments announced 

 some years ago, as made by Morichini, that steel wire, when 

 exposed for a certain time to the violet rays of the sun, are con- 

 verted into magnets. These experiments had been tried by 

 various philosophers, and generally without success, though 

 there were some who affirmed that they had verified jMorichini's 

 -discovery. The reality of this power of the violet rays, however, 

 was generally doubted till it was announced by the editors of 

 the iiibliotheque Universelle that the late Professor Playfair had 

 witnessed a successful experiment of this kind. Since that 

 period various other persons have tried this experiment with 

 considerable industry ; but, as i'ar as I have heard, without the 

 least success. A set of unsuccessful trials by M. Dliombres 

 Firmas is related in the Annalos de Chimie et de Physique, tom. 

 X. p. 285. I have sometimes been tempted to suspect that 

 Morichini's success in this experiment may have depended upon 

 the position of his needles during his experiments. If the 



