Sijnthesis of White Light from the Colours of the Spectrum. 261 



moniochloride ; and that, consequently, that ammonia which con- 

 stitutes the difference between them is not the same in proper- 

 ties as free ammonia. Hence, as has been already seen, ammonia 

 does not convert the pentammoniochloride into hexammonio- 

 chloride unless water be present to effect a decomposition. 



(6) If we consider the nature of the oxides which these poly- 

 ammoniacal cobaltic chlorides generate when decomposed by 

 heated water, we shall perceive that the formulse of the latter 

 ought to be doubled, — the argument being in principle the 

 same as that for doubling the formula of ferric chloride if it 

 were written FeCl 3 . The illegitimacy of rational formulse having 

 the general character 



*NH 3 . CoCl 3 



for these bodies is also evident when we call to mind that an 

 ammoniacal salt and an oxidizing agent are not only their pro- 

 ducers, but their products of decomposition, — facts to which such 

 formulse do not refer, while they represent reactions which have 

 not yet been recorded by a single experimenter. 



XXIX. Synthesis of White Light from the Colours of the Spec- 

 trum. By C. J. Woodward, B.Sc. 



To the Editors of the Philosophical Magazine and Journal. 

 Gentlemen., 



THE following demonstration of the synthesis of white light 

 is, I believe, new; it occurred to me one evening when 

 using Newton's disk. 



The spectrum from a bisulphide-of-carbon prism was thrown, 

 by means of a small mirror held in the hand, on to a screen ; 

 on moving the mirror to and fro so as to cause the spectrum to 

 move over itself in the direction of its length, there was formed 

 a band of white light, identical in appearance with a beam of 

 white light received direct from the source of light and then 

 similarly thrown upon the screen by the moving mirror. 



By using suitable diaphragms, so as to stop out certain co- 

 lours, the compound colour resulting from the remaining colours 

 may of course be shown. 



I am, Gentlemen, 



Your obedient Servant, 



C. J. Woodward. 

 Midland Institute, Birmingham, 

 March 11, 1868. 



Phil. Mag. S. 4 Vol. 35. No. 237. April 1868. T 



