16 Spectrum Method of Detecting Blood. 



a small amount of blood. However, on adding a small excess of 

 boric acid, the bands of the cochineal are made more faint, and very 

 considerably raised towards the blue end, so as to leave the red end 

 of the green clear, whilst those of oxidized haemoglobin are not 

 changed, and that nearer the red end, if not both, can be seen 

 perfectly well. By proceeding in the usual manner, there is no 

 great difficulty in recognizing the darker band of deoxidized 

 hsematin. 



Other special difficulties might occur in particular instances, 

 but I trust that these examples will suffice to show how they may be 

 overcome. I do not now know of any that require special remarks ; 

 and, as far as I am able to judge, we need never despair of detectiug 

 blood, so long as any haematin remains undecomposed. Fortunately 

 it resists decomposition so well, that this would rarely happen in 

 ordinary cu'cumstances ; but yet there are cases in which it does 

 occur, as, for example, when acted upon by strong ozone, or other 

 powerful oxidizing reagents. 



It is quite possible that stained garments might have been 

 washed, and some of the water employed might be obtained. If 

 no soap had been used, this water could be examined in a long tube 

 of thick glass, ten inches or more in length, and a quarter of an 

 inch in internal diameter, permanently closed at one end with a 

 circular piece of plate glass, and, when filled, covered over at the 

 other with another glass. For examining solutions in such tubes a 

 small pocket spectroscope, such as recently made for me by Mr. 

 Browning, is extremely convenient, and suitable in every respect. 

 If only two or three days old, the bands of oxidized haemoglobin 

 might be seen ; but if the solution had been kept longer, and they 

 could not be detected, it should be concentrated by evaporation at a 

 gentle heat, and tested for haematin. If during evaporation any 

 deposit be formed, insoluble in cold dilute ammonia, it should be 

 dLssolved by the aid of heat. When soap is used in washing off 

 stains, the alkali soon changes the haemoglobin into haematin, and 

 the soap makes the solution inconveniently turbid and opaque. It 

 is best in such a case to agitate the suspected soap and water with 

 ether, remove it with a pipette, after the two hquids have com- 

 pletely separated, and repeat the process over and over again, with 

 fresh ether, until the aqueous solution at the bottom has become 

 quite clear and free from soap. It should then be concentrated by 

 evaporation, and examined for haematin, as usual. Of course in all 

 such cases it would be desirable to test the solution as soon as pos- 

 sible, lest decomposition should occur, but by these means a very 

 small quantity of blood, that would show no colour, might be recog- 

 nized within a week or two, but probably not after. 



For the detection of blood in urine, a tube about ten inches 

 long is very suitable. If turbid it should be filtered ; but, since a 



