1813.] Chemical Properties of Animal Fluids. 19$ 



bow, when the drops are about 3 ' or v i of an inch in 

 diameter. It is remarkable that in such cases the original rain- 

 bow is altogether wanting, and probably for a similar reason, 

 we scarcely ever see a rainbow in a cloud which does not con- 

 sist of drops so large as to be actually felling, although I have 

 once seen such a rainbow ending abruptly at the bottom of a 

 cloud : it may be conjectured that the edge of the light is in such 

 cases so much weakened by diffraction, that it is too faint to ex- 

 hibit the effects occasioned by a larger drop. Dr. Smith has 

 made a remark somewhat similar, (Opt. r. 501,) which, if not 

 completely satisfactory upon the principles which have been 

 mentioned, is certainly altogether unintelligible upon his own. 

 The coloured circles, immediately surrounding the shadows 

 of the observers, may be deduced from the effect of the same 

 minute particles of water, upon the light which has been four, 

 and perhaps five, times reflected within the drops, which may, 

 after transmission, coincide in direction with another portion, 

 passing on the opposite side of the centre; and the drops about 

 3 '„ ' U or TgVff of an inch in diameter would in this manner pro- 

 duce a faint corona, of such magnitude, that the limit of green 

 and red, employed in the use of the eriometer, should be at the 

 distance of about five degrees from the centre of the shadow ; 

 which, as nearly as I could estimate it, was its real distance in 

 the appearance that I observed. 



Article VI. 



General Views of the Composition of Animal Fluids. By J. 

 Berzelius, M. D. Professor of Chemistry in the College of 

 Medicine at Stockholm. 



(Continued ft om y. 26.) 



Inquiry into the Influence of the Iron contained in the Colouring 



Mutter, in producing its Colour. 



The greatest chemical difference that is found between fibrin, 



albumen, and colouring matter, consists in a quantity of oxide 



of iron being contained in the ashes of the colouring matter, 



while none, or at least an infinitely small portion, is afforded by 



the others. Parmentier and Deyeux, to whom we are indebted 



for an elaborate memoir on the blood, have conjectured that the 



iron, contained in the blood, was dissolved in a way analogous 



to the alkaline tincture of Stahl, an opinion which has since 



!>' en controverted by Fourcroy and Vauquelin, who, on theii 



QdeavOOfed to prove that the colouring matter of the 



u 2 



