342 Mr. W. J. Sell and Prof. W. J. Lewis. [Feb. 14, 



yellow plates is produced. This beautiful compound is sparingly soluble 

 in cold, more readily in hot water, especially in presence of alkaline 

 bromides, and crystallises out in large prismatic aggregations ; 

 alcohol especially when warm takes up the substance, freely decom- 

 posing it and depositing the normal bromide, a similar result being 

 obtained with ether and carbon disulphide, in which, however, it is 

 much less soluble. The crystals rapidly lose bromine on exposure to 

 the air, yielding bright-green pseudomorphs of the normal bromide. 

 A specimen of the compound in the form of micaceous scales exposed 

 for three days over lime gave 36*5 per cent, of bromine, against 36*78 

 required for the normal salt. 



Analysis leads to the conclusion that this substance has a similar 

 composition to that of the periodide, viz., (CON 2 H 4 ) 12 <> 2 Br 6 6Br 2 . 



The following determination was made : 



1*2668 gram salt was dissolved in dilute sulphurous acid, and all 

 excess of the latter expelled by heat. The solution was mixed 

 with excess of silver nitrate, and the whole pretty strongly acidified 

 with nitric acid, gave 1*91468 gram AgBr. 



Percentage calculated. Percentage found. 

 Br ........ 63-58 64*16 



Sulp hatoperbromide. 



This compound is precipitated in green needles when a solution of 

 any salt of the base is mixed with dilute sulphuric acid and bromine- 

 water added. It is sparingly soluble in water, and loses bromine 

 gradually on exposure to the air. The composition is similar to the 

 sulphatoperiodide, viz. : 



This requires per cent. : 



Found. 

 SO 4 ........ 12*82 12*97 



Br ......... 32*06 34*16 



The well-marked crystallisations presented by the substances here 

 described, prove them to be definite compounds. Their empiric 

 formulas, as derived from analysis, are as to complication such as 

 chemists have been wont to expect only in organic substances ; and 

 the rational formulae provisionally assigned to them would hardly 

 have suggested themselves without the clues afforded by the materials 

 and processes employed in their formation. The examination of the 

 decompositions which they undergo under varied conditions, is a 

 problem little more than touched upon, and the same may be said of 

 the action of chromyl dichloride on substituted ureas, including 



