New Substance discovered in Davidsonite. 433 



'2. When heated to redness, it glowed like tinder, and 

 became white. 



3. In dilute muriatic acid, it effervesced, and was con- 

 verted into a white powder. 



4. When placed in a charcoal crucible, properly enclosed, 

 and heated strongly in a forge for half an hour, it was not 

 altered. 



It seems probable, that the slate-blue substance consisted 

 of metallic Donium, but in a state of intimate division ; 

 while from the experiments made upon the oxides, upon 

 which, however, for many reasons, great confidence can- 

 not be placed, it would appear that the oxides are composed 

 of 



1. The Buff . . 94-89 Donium + 5-11 oxygen. 



2. The White . 83-66 Donium + 16-34 oxygen. 

 Or, that the white oxides contains thrice as much oxygen 

 as the buff. 



Although circumstances do not permit of my continuing 

 this investigation, I have reason to believe that it will not 

 be laid aside, but that a more full account of this substance 

 will shortly be given by an individual much more capable 

 of performing the task. 



Article VII. 



On a difficulty in Isomorphism, and in the received constitution 

 of the Oxygen Salts ; in a Letter to Professor Mitscher- 

 lich, of Uerlin, from Thomas Clark, M. D., Professor 

 of Chemistry in Marischal College, Aberdeen.* 



Sir, — I do myself the honour of addressing to you some 

 observations tending to remove, in your doctrine of Iso- 

 morphism, a discrepancy arising from a fact stated in your 

 valuable paper on the Acids of Manganese. The proposed 

 observations have an immediate object that happens to be 

 of the greater interest, inasmuch as they cannot accom- 



* Dr. Clark uses the Continental symbols and atomic weights, omitting minute 

 fractions. But chlorine, instead of CI. he makes Ch. ; Sodium, So.; Silver, Sv. ; 

 on account of his considering their weights as double those used on the Con- 

 tinent. — Edit. 



VOL. III. 2 r 



