1865.] Soeby on Detection of Blood-Stains by Spectrum-Analysis. 213 



few drops of water with citric acid in a watch-glass, and proceeding 

 as already described, a most unmistakable spectrum like No. 8 may be 

 obtained, even when the stain is only half-an-inch square, and scarcely 

 visible. In attempting to remove a blood-stain from cloth by sponging, 

 on the first application of the water a solution of blood would be 

 formed, and run into the surrounding cloth by capillary attraction. 

 Hence, though the stain may appear to have been removed, the cloth 

 round about might, and probably would, retain abundance of the 

 colouring matter, which could be dissolved out. Any suspicious marks 

 that might be due to such treatment should therefore be examined with 

 care. Of course, in such cases the microscope alone would be of no 

 avail, and mere chemical tests could not be relied on, and thus the 

 spectrum method becomes especially useful. Specimens of this cha- 

 racter having been placed in the hands of some of the first authorities 

 in such inquiries, they said that neither they nor anyone else could 

 make out anything from them ; nor would they believe that I could, 

 though the amount of blood was such that in a few minutes I could 

 have shown such a spectrum as No. 8, and have been in a position to 

 give evidence with great confidence. 



When soap is present it causes a precipitate ; but this is quite 

 soluble in plenty of ammonia, and does not prevent our seeing the 

 spectrum No. 8. Boiling water, instead of facilitating the removal of 

 blood, makes it more fixed, by coagulating the albumen. If the blood 

 be dried on glass, the colour is changed to a brownish red, and it gives 

 a spectrum like No. 5, whether dry or damp. When dissolved by 

 citric acid, it yields haematin, and readily gives spectrum No. 8. 



In some cases foreign matters, or the mordants, make the solution 

 so turbid that it is difficult to see the spectrum to advantage. If we 

 wish to observe the spectrum of blood in its natural state, or as it 

 becomes by mere exposure to the atmosphere, it is better not to filter, 

 but to allow the solution to stand in the cell in front of the slit, until it 

 has become sufficiently clear ; because filtering would probably remove 

 much of the colouring-matter of the blood. However, in some varie- 

 ties of brown cloth the mordants give rise to such a turbid solution, 

 that it is very difficult to see the spectrum in a satisfactory manner. 

 Citric acid should therefore be added to make the colouring-matter 

 more completely soluble, and the liquid filtered. For such small 

 quantities a blotting-paper filter f of an inch in diameter should be 

 used. It can be conveniently supported on a platinum wire bent at 

 one end into a ring, and made to slide up and down a small wire for 

 a support ; and if the bottom of the filter touch the cell or watch- 

 glass, though the liquid may pass through slowly, the final result is 

 far more satisfactory. After the acid solution has passed, it is well 

 to add the ammonia by allowing it also to go through the filter, to 

 carry away any colouring-matter, soluble in that reagent, that might 

 remain on the filter. 



Though in actual practice many other facts may turn up to render 

 special modifications necessary, yet the following is the method I 

 should adopt in examining a mark or stain supposed to be due to 

 blood, assuming that only a small quantity was at my disposal. I 



