138 



Prof. T. Carnelley on the -Colour 



R. 



CoR 2 . 



NiR 2 . 



PdR 2 . 



Eu 2 R 6 . 



Ir 2 R 6 - 



IrR 4 . 



PtR 2 . 



PtR 4 . 



CI ... 



Br ... 

 I 



blue 

 green 

 black 



yellow 

 golden 

 black 



red 4 



black 



yellowish 

 brown 



black 



j- green 

 black 



red 



black 



olive 

 brown 

 black ( 



orange 



brown 



brown- 

 ish-black 



In the above tables, elements belonging to even series are 

 printed in ordinary type, and those belonging to odd series in 

 thick type, so that it may be seen at a glance which compounds 

 are comparable with one another. The arrows also show the 

 direction and the extent to which these comparisons may be 

 made. 



I have collected in the tables all the available data. The 

 colour attached to each compound is that given in the ordinary 

 text-books, in Watts's Dictionary, and in Gmelin's Handbook. 

 In cases where two different authorities do not agree, I have 

 either given both or have taken the colour of the actual speci- 

 men in our college museum. Some compounds, such as Hgl 2 , 

 HgO, HgS, Sb 2 S 3 , &c, exist in two differently coloured allo- 

 tropic modifications*, iii which case both colours are entered. 

 In some few instances also there is given in addition to the 

 colour (c) when cold, the next colour (/*) which the compound 

 assumes on heating, and sometimes the subsequent colour 

 (hh) which it assumes when still more strongly heated. 



It should not be forgotten that the rule formulated above 

 strictly applies only to compounds in the solid state, and, 

 further, that even in the solid state the colour is liable to vary 

 somewhat with the state of aggregation. In general the 

 colours given in the tables refer to the powdered or precipi- 

 tated condition. 



From the tables it will be seen that out of 426 cases jin 

 which the rule may be applied there are but 14 exceptions, 

 viz. : Au 2 0, CdO, TiBr 4 , PBr 5 , OCl 2 , WC1 4 , Cr0 2 Cl 3 , DiCl 3 , 

 V 2 5 , Cr0 3 , WI 2 , UC1 5 , UC1 4 , and Aul 3 . Of these, two, 

 viz. OCl 2 and Cr0 2 Cl 2 , may be omitted, as the colours given 

 are those of the liquid compounds, whereas the rule, as stated 

 above, is only considered to be applicable to the solid state. 

 According to the rule TiBr 4 and PBr 5 should be white, whereas 

 these compounds are generally stated to be pale yellow : it is 

 possible that the pure compounds are really white or colourless, 



* Depending no doubt on a difference in the size of the molecule, and 

 in such a way that the modification with a colour nearest the red eud of 

 the spectrum will have the largest molecular weight. 



