390 Royal Institution : — ■ 



well-marked dark bands in the yellow and green.] These bands, first 

 noticed by Hoppe, are eminently characteristic of blood, and afford a 

 good example of the facilities which optical examination affords for 

 following a substance which possesses distinctive characters of thib 

 nature. On adding to a solution of blood a particular salt of copper 

 (any ordinary copper salt, with the addition of a tartrate to preve* 

 precipitation, and then carbonate of soda), a fluid is obtain 

 utterly unlike blood in colour, but showing the characteristic banc 

 of blood, while at the same time a good deal of the red is absorbed 

 as it would be by the copper salt alone. On adding, on th^ 

 other hand, acetic acid to a solution of blood, the colour is merely 

 changed to a browner red, without any precipitate being produced 

 Nevertheless, in the spectrum of this fluid the bands of blood have 

 wholly vanished, while another set of bands less intense, but still 

 very characteristic, make their appearance. This alone, however, 

 does not decide whether the colouring matter is decomposed or not 

 by the acid ; for as blood is an alkaline fluid, the change might be 

 supposed to be merely analogous to the reddening of litmus. To 

 decide the question, we must examine the spectrum when the fluicS 

 is again rendered alkaline, suppose by ammonia, which does nc 

 affect the absorption bands of blood. The direct addition of ammo- 

 nia to the acid mixture causes a dense precipitate, which contains 

 the colouring matter, which may, however, be separated by the use 

 merely of acetic acid and ether, of which the former has been already 

 used, and the latter does not affect the colouring matter of blood. 

 This solution gives the same characteristic spectrum as blood to which 

 acetic acid has been added ; but now there is no difficulty in obtain- 

 ing the colouring matter in an ammoniacal solution. In the spec- 

 trum of this solution, the sharp absorption bands of blood do not 

 appear, but instead thereof there is a single band a little nearer to 

 the red, and comparatively vague [this was shown on a screen]. 

 This difference of spectra decides the question, and proves that ha?- 

 matine (the colouring matter prepared by acid, &c.) is, as Hoppe 

 stated, a product of decomposition. 



The spectrum of blood may be turned to account still further in 

 relation to the chemical nature of that substance. The colouring 

 matter contains, as is well known, a large quantity of iron ; and ; 

 might be supposed that the colour was due to some salt of iron 

 more especially as some salts of peroxide of iron, sulphocyanide fcr 

 instance, have a blood-red colour. But there is found a strong 

 general resemblance between salts of the same metallic oxide as 

 regards the character of their absorption. Thus the salts of sesqui- 

 oxide of uranium show a remarkable system of bands of absorption 

 in the more refrangible part of the spectrum. The number and 

 position of the bands differ a little from one salt to another ; but 

 there is the strongest family likeness between the different salts. 

 Salts of sesquioxide of iron in a similar manner have a family like- 

 ness in the vagueness of the absorption, which creeps on from one 

 part of the spectrum to another without presenting any rapid transi- 

 tions from comparative transparency to opacity and the converse. 



