BLOOD STAINS 105 followed by a drop of tannic acid solution produces a blue or bluish-purple colouration, if it is due to oxide of iron. Synthetic Dye Stains.—These stains often resemble old blood stains, but they may be easily recognized by treating them with strong acids and alka- lies. Nitric acid, for example, changes them to a yellow colour and a strong solution of an alkali may restore the red colour'in most cases. No such re- action takes place in the case of blood stains. Mineral Stains.—These are mostly due to red paints containing oxides of iron. After dissolving with hydrochloric acid, the solution may be tested for iron. In certain circumstances, stains of red paint, consisting of red lead or red sulphide of mercury (vermilion) are found in the garments of Hindu women or in Hindu temples. They can be easily identified by the applica- tion of chemical tests for lead and mercury. Stains of Vegetable Origin.—Stains resembling blood may be produced on clothing from certain fruits, such as, mulberry, currants, mangosteens, gooseberries and jambans (Eugenia jarnbolana). They are changed to a greenish-yellow colour on the addition of ammonia and are bleached by chlorine water, which has practically no effect on blood. Knives which are used to cut acid fruits not unfrequently present stains having a strong resemblance to blood stains. These stains are due to the formation of citrate and malate of iron, are soluble in water, and give rise to Prussian blue, if a drop of hydrochloric acid and potassium ferrocyanide solution be added. They do not show red blood corpuscles under a microscope, but present vege- table cells and detritus. Reddish stains are also produced by henna, catechu, pan juice (with lime and catechu), tobacco, and by the barks, leaves and fruits of some trees, such as babool (Acacia Arabica) and gab (wild mangosteen or Diospyros Embryopteris). Most of them grow all over India and contain tannin, which will blacken the stain if a drop of ferric chloride solution is added to it. The addition of ammonia will change the colour to green, red or bluish-black, and dilute mineral acids will heighten the original colour, while chlorine water will bleach it. An acid decolourises a stain caused by pan juice, while an alkali restores its colour. The spectroscope does not show any absorption bands. Certain red colouring matter, such as cochineal, lac dye, alkanet root, madder red, muujeet (Sanskrit—Manjistha) and petals of red hibiscus, give spectra which may be mistaken for those of blood, but the positions of the absorption bands in these spectra are not identical with those of haemoglobin and its derivatives nor are they affected by reducing and other reagents in the same way as haemoglobin changes to oxyhsemoglobin, haemochromogen, etc. Moreover, these colouring matters do not give the benzidine reaction in the preliminary chemical tests, and their solutions, when treated with alum, boric acid, dilute ammonia, sulphur dioxide solution or chlorine water, show well-marked alterations in the tone and depth of their colour, as also in the position of their absorption bands. Such changes never occur if the colour- ing matter is blood. Other Stains.—Spots of grease, resin, tar and pitch, especially on dark fabrics, may resemble very old blood stains, but their solubility in alcohol, ether, chloroform, turpentine or xylol differentiates them from blood stains. When a clean white filter paper is pressed on any of these spots with a hot iron the paper absorbs the material and is stained. Reddish-brown faecal stains sometimes simulate old blood stains. Even the benzidine test may show a positive reaction owing to the presence ^of undigested fish or meat fibres. An examination under a microscope will, however, reveal the undigested food particles and decide the question.