Accidental and Complementary Colours. 297 



combined with those of the second surface, produce white 

 light. 



4th. That an attraction and repulsion exists between 

 colours. Colours of a like kind attract each other, and 

 those of an unlike kind repel each other. 



Thus, when a coloured object is placed on a white ground, 

 the colour of such object attracts the rays of the same 

 colour as itself from the contiguous white ground, and 

 leaves a portion of the latter of the complementary tint. 



5th. Hence, the theory of accidental and complementary 

 colours, which may be included in the following proposi- 

 tion, viz. : 



That a coloured body has the power of decomposing white 

 light ; of attracting and retaining rays of a like kind to itself; 

 and the other rays, which it repels, constitute the accidental 

 or complementary impression. 



Charles Tomlinson. 



Brown Street, Salisbury, 

 December, 1835. 



Article V. 



Economical Mode of forming Hyper-manganate of Potash. 

 By William Gregory, M. D., F. R. S. E., Lecturer 

 on Chemistry, Edinburgh. 



{To the Editor of the Records of General Science.) 



Sir, — Observing in the Records of General Science, for 

 September, 1836, part of a memoir by Professor Mitscher- 

 lich, on the Manganic and Hyper-manganic Acids and their 

 Salts, it has occurred to me, that your readers may like to 

 be acquainted with the following easy and economical 

 method of obtaining the most remarkable of these com- 

 pounds, the hyper-manganate of potash. 



My process is a modification of that of Wohler, who re- 

 commends to melt chlorate of potash along with caustic 

 potash in a platinum crucible, and to add peroxide of man- 

 ganese to the fused mass. 



There are several objections to this process. In the first 

 place, the melted mass froths up violently when the last 

 portions of oxygen escape, so that we can only employ a 

 small quantity of materials, even in a pretty large crucible. 



