spectrum Method of Detecting Blood. 11 



in a very short time, and the presence of a stronger acid on dirty- 

 clothes may at once alter the haemoglobin into hgematin. 



On digesting in water a stain that has been kept until all the 

 haemoglobin has disappeared, the methtemoglobin dissolves. When 

 the solution is sufficiently strong, this shows a band in the red, and 

 two fainter in the green. The addition of ammonia removes that in 

 the red, makes those in the green much darker, and develops a spe- 

 cial very narrow band in the orange. When deoxidized this solution 

 gives deoxidized haemoglobin. Since methaemoglobin is formed at 

 once from haemoglobin by the action of a great number of different 

 oxidizing reagents, and since it can be reconverted into oxidized 

 haemoglobin by slight deoxidization, I am inclined to look upon it 

 as a peculiar oxidized modification. On adding a little of the double 

 tartrate and of the ferrous salt to even a dilute solution from an old 

 stain, the methaemoglobin is deoxidized, and the well-marked spec- 

 trum of fresh blood can be seen. If left too long, the spectrum of 

 deoxidized haemoglobin is developed, but on well stirring, that of the 

 oxidized reappears, and the various other spectra may afterwards be 

 obtained, as described above. That part of the stain, insoluble in 

 water, which is chiefly haematin, may be dissolved in dilute citric 

 acid or ammonia, and when deoxidized the spectrum seen to even 

 greater advantage than when fresh blood is employed, because there 

 is no general shading in the green, due to there having been 

 methasmoglobin mixed with the haematin. We may thus obtain an 

 excellent spectrum from a blood-stain nearly fifty years old. In 

 very old stains all the methaemoglobin has disappeared, and some- 

 times even a considerable part of the haematin has been altered into 

 another brown colouring matter, which does not give any well- 

 marked spectrum. 



When a blood-stain has been made sufficiently hot to coagulate 

 the albumen, neither water, citric acid, nor cold ammonia wlU dis- 

 solve it, but by heating in dilute ammonia the haematin is easily 

 dissolved, and may be detected either before or after concentrating 

 the solution by evaporation. I may here say that the spectrum of 

 deoxidized haematin can in no way be better seen than by deoxidizing 

 a solution of fresh blood that has been boiled with dilute ammonia, 

 which gives rise to a very pure haematin. 



In applying these principles to the detection of suspected stains, 

 it is desirable in the first place to examine a portion of the unstained 

 fabric, to ascertain whether any colour is dissolved from it by water, 

 and whether the solution has an acid, or alkaline, reaction. It is 

 also important to ascertain whether colour is dissolved from the 

 fabric by dilute citric acid or dilute ammonia, and if so, to deter- 

 mine whether this would in any way interfere with the recognition 

 of blood by the processes described above. In the case of scarlet 

 cloth and of some other red fabrics, much colour is dissolved out by 



