7o POISONS : THEIR EFFECTS AND DETECTION. [§ 41 , 
2. Preparation of Hsematin Crystals (Teichmann’s crystals).—A 
portion of the borax solution is diluted with 5 or 6 parts of water, and 
one or more drops of a 5 or 6 per cent, solution of zinc acetate added, 
so long as a brownish-coloured precipitate is thrown down. The 
precipitate is filtered off by means of a miniature filter, and then 
removed on to a watch-glass. The precipitate may now be dissolved 
in 1 or 2 c.c. of acetic acid, and examined by the spectroscope it will 
show the spectrum of hsematin. A minute crystal of sodium chloride 
being then added to the acetic acid solution, it is allowed to evaporate 
to dryness at the ordinary temperature, and crystals of hsematin hydro¬ 
chlorate result. There are other methods of obtaining the crystals. 
When a drop of fresh blood is simply boiled with glacial acetic acid, 
on evaporation, prismatic crystals are obtained. 
Hsematin is insoluble in water, alcohol, chloroform, and in cold dilute 
acetic and hydrochloric acids. It may, however, be dissolved in an 
alcoholic solution of potassic car¬ 
bonate, in solutions of the caustic 
alkalies, in boiling acetic and hydro¬ 
chloric acids, and in Riegler’s re¬ 
agent. Hoppe-Seyler ascribes to 
the crystals the formula C 68 H 70 N 8 
Fe 2 O 10 2HCl. Thudichum considered 
that the pure crystals contain no 
chlorine, and are therefore those of 
hsematin. It is the resistance of 
the hsematin to decomposition and 
to ordinary solvents that renders it possible to identify a certain stain 
to be that of blood, after long periods of time. Dr Tidy seems to 
have been able to obtain blood reactions from a stain which was sup¬ 
posed to be 100 years old. The crystals are of a dark red colour, and 
present themselves in three forms, of which that of the rhombic prism 
is the most common (see fig.). But crystals like b, having six sides, 
also occur, and also crystals similar to c. 
If the spot under examination has been scraped off an iron implement 
the hsematin is not so easily extracted; but Dragendorff states that borax 
solution at 50° dissolves it, and separates it from the iron. Felletar has 
also extracted blood in combination with iron rust, by means of warm 
solution of caustic potash, and, after neutralisation with acetic acid, has 
precipitated the hsemin by means of tannin, and obtained from the 
tannin precipitate, by means of acetic acid, Teichmann’s crystals. A 
little of the rust may also be placed in a test tube, powdered ammonium 
chloride added, also a little strong ammonia, and after a time fitered ; 
a small quantity of the filtrate is placed on a slide with a crystal of 
sodium chloride and evaporated at a gentle heat, then glacial acetic acid 
