208 Mr, Charles Tomlimon on 



pregnated with the copper mordant becomes a little darker 

 and brown-red. The solution of madder, on the other 

 hand, contains much gummy matter, and the madder itself 

 has a dark brown colour. It is obvious, therefore, that the 

 solution of madder dissolves oxide of copper and thereby 

 precipitates the greater portion of the colouring matter. 

 Even treating the cloth before dyeing with cow-dung, pro- 

 duces no alteration. If both pieces of cloth are dyed at 

 once with the same quantity of madder, no madder red is 

 obtained on the one but a somewhat darker orange, and the 

 other mordanted with copper mordant will be as dark again 

 as it was before. For this reason ; that on the first dyeing 

 the madder is prevented by the oxide of copper from being 

 dyed darker. 



Hence, it is a rule with manufacturers not to introduce 

 copper into alum mordants, intended for madder red. 

 Even a small quantity of copper taken up by boiling the 

 solution of alum in an untinned copper vessel, acts inju- 

 riously. For the same reason we cannot extract in a copper 

 vessel the madder red from madder with muriate of alumina. 

 It precipitates with the oxide of copper. 

 ( To he continued.) 



Article VIII. ^ 



A Theory of Accidental and Complementary Colours, 

 By Charles Tomlinson, Esq.''^ 



1 . If we close one eye, and place before the other a disk 

 of coloured glass, green, for instance, and through this 

 medium view a sheet of white paper, the sudden removal 

 of the disk from the eye will cause the paper to assume a 

 bright red appearance ; f and if the disk be instantly re- 



* This paper would have appeared long since in continuation of my paper, 

 vol. ii. page 283, had it not been for a revised publication, by M. Plateau, of the 

 First Part of his theory, wherein he repudiates his former publication as incom- 

 plete. I have waited many months, and the Second Part of his publication has 

 not appeared. I, therefore, venture to publish my theory without reference to 

 M. Plateau. My papers on this subject, already published in the Records, will 

 be found vol. i. page 439, vol. ii. pages 21 and 283. Mr. Cooper's papers appear 

 in vol. ii. pages 108 and 172, and vol. iii. page 99. 



t The change from green to red may be strikingly observed, by substituting a 

 taper in a room where there are no other lights for the sheet of white paper. The 

 former is best seen by night, and the latter by day. In both cases, a pair of dark 

 green spectacles is, perhaps, preferable to a green disk. 



