Mac Culloch on Animals preserved in Amber. 43 



some loss of shape, from mechanical violence, or other causes, 

 connected with its present mineral position. 



But it frequently happens that this test becomes of no use; as 

 the specimens are often cut and polished into such forms as to 

 show the enclosed insect to advantage. Even in these cases, 

 however, the colour and appearance of the resinous matter which 

 encloses the insects, are always somewhat different from those 

 of amber; or they are always, at least, such that a practised 

 eye can pronounce on the genuine specimen; can distinguish be- 

 tween resin and amber. A paleness of colour is invariable in the 

 resin; and if amber is not always of a full yellowish brown, the paler 

 varieties have a peculiar tinge of yellow which never exists in the 

 resin ; the colour of these is comparatively watery, thin, and feeble. 



The striking character, however, to a practised eye, is a pe- 

 culiar lustre in amber which is wanting in the resin; arising, pro- 

 bably, from a higher refractive density, and easily recognised 

 when once pointed out; but difficult to describe in words. 



To those to whom characters of a nature so delicate are in- 

 sufficient, it is necessary to point out other more unquestionable 

 and easier modes of discriminating the two without injuring the 

 specimens. 



It is proper, in the first place, to remark, that the electrical 

 property is not a sufficient test; although it is that to which an 

 appeal is commonly made. The resins, like amber, are electrical 

 on friction, and the electricity of both is negative. But, on 

 strongly rubbing the resins, they give out a smell quite different 

 from that which is elicited from amber in the same circumstances. 

 To describe these odours, is evidently impossible ; but as they 

 can never be mistaken for each other when once known, it will be 

 necessary for the collector of specimens to render himself ac- 

 quainted with both ; by making the necessary experiments on 

 genuine specimens of common amber, and on specimens of that 

 resin which, if it is not the substance in question, agrees with 

 it in its ostensible properties, namely, gum animi, as it is com- 

 monly called. 



It would obviously be easy to supply chemical tests for the 



