Page images

amination; the microscopical test, which, in many cases, is undoubtedly of great value, we shall leave to those who are sufficiently qualified to escape its fallacies. The former mode of testing admits of more extended application than the latter, since we can detect the constituents of the blood by chemical reactions, in cases where the microscopical test fails to discover even the slightest trace.

§ 132. We shall first consider the case where the spots are on undyed cloth, linen, or cotton. The stains appear of a more or less dark, red-brown, or black-brown color, and impart to the cloth a kind of stiffness. A spot is cut out, and suspended in a small quantity of distilled water; it softens, reddish-brown stripes are produced in the water, and the stains disappear from the cloth more or less completely.

The liquid thus obtained, which is of a reddishyellow, or brown color, is heated in a test-tube. If the stain consisted of blood, the liquid looses color, becomes opalescent, and sometimes greyish-white, flakes of coagulated albumen are observed to separate. If, then, a solution of nitrate and nitrite of mercury* is added, and heat applied, the flakes assume a brick-red, or brownish-red color of more or less purity. The same reaction is obtained on adding the mercury solution directly to the liquid under examination, and applying heat.

On addition of nitric acid to the liquid, whitish flakes separate; on heating, they assume a more or less pure yellow color.

* This solution, the best reagent for proteinaceous bodies, is prepared by dissolving mercury in an equal weight of red, fuming nitric acid, and adding to the liquid twice its volume of water.

Chlorine-water produces white flakes, especially on heating

A solution of tannine gives a whitish precipitate.

On adding to the liquid a few drops of acetic acid, and subsequently a drop of ferrocyanide of potassium, a white precipitate, or turbidness is produced.

The flakes of coagulated albumen, which formed on heating the liquid, dissolve on addition of a few drops of caustic soda; they are re-precipitated from this solution on addition of nitric acid, or chlorinewater.

On evaporating the liquid in a porcelain dish, a brown, lustrous coating remains; on pouring chlorine-water on it, and again evaporating, a colorless residue is obtained, which, on addition of a little water and sulphocyanide of potassium, assumes a reddish color (owing to the iron of the blood).

$ 133. If the liquid (the solution of the stain in water) is mixed with some pure carbonate of potassa, the mass evaporated, the residue heated to dryness at 100° C.; then placed in a long and narrow glasstube, covered with some dry carbonate of potassa, and strongly and continuously heated by means of the blow-pipe, a mass is obtained which contains cyanide of potassium. When the tube has cooled, it is cut off above the fused mass, and the latter, together with the lower end of the tube, thrown into a test-tube; some water and a few particles of iron filings, or better, sulphuret of iron, are added, and gently heated. Ferrocyanide of potassium is formed. The liquid is filtered, the filtrate slightly acidulated with hydrochloric acid, and mixed with a few drops of sesquichloride of iron; the liquid assumes a greenish, or bluish color, and deposits, after a while, a precipitate of Prussian blue (Löwe, Pharm. Centralblatt. 1854. p. 137).

In order to obtain this characteristic reaction, we may also treat the spots with alkaline water, add carbonate of potassa to the extract, then evaporate, etc.

Or the cloth containing the spots is calcined in a porcelain capsule until it is easily rubbed to powder, and mixed with carbonate of potassa ; this mixture is then strongly ignited, and otherwise treated, as before.—( Wiehr, Pharm. Centralblatt. 1854. p. 431).

It is evident that these experiments require the absence of all other nitrogenized bodies; and it should, therefore, not be neglected to submit a piece of the unstained cloth to exactly the same treatment.

§ 134. If an attempt has been previously made to remove the stains by means of boiling water, nothing will be dissolved by a subsequent treatment with water, because the albumen has become coagulated. In this case, water is used, which contains some caustic potassa ; the resulting solution gives white precipitates with nitric acid, hydrochloric acid, and chlorine water, and the presence of a proteinaceous substance may be shown by the treatment described in $ 133

The stains, by being treated with alkaline water, do not lose their color. If then exposed to the action of hydrochloric acid, the coloring matter is dissolved; on evaporating the solution to dryness, a residue is obtained which becomes blue with ferrocyanide of potassium, and red with sulphocyanido of potassium.-(M. Morin, faits pour servir à l'histoire du sang, considéré sous le rapport de la chimie légale, private communication.)

$ 135. If the stains are on dyed, or printed linen, or cotton clothes, the spots are cut out, and macerated with water, as in the preceding case. If the colors are fast, the same kind of solution is obtained; but, if they are wholly, or partially soluble in water, the coloring matter of the blood becomes mixed with the dyes, and the reactions which this solution gives with the proper reagents will not be so distinct, or so conclusive for the presence of blood as in the case of undyed stuffs. In this case, the formation of cyanide of potassium is the principal reaction; the process is the same as that described § 133. It is necessary that an unstained piece of the cloth be subjected to the same treatment, and only if here no similar reaction is observed, we can rest satisfied that the cyanide was not produced from the constituents of the dye. The same remark applies to the case where the stains have been macerated in alkaline water.

$ 136. Stains on woollen stuffs are first macerated in water, in order to obtain a solution which may be tested with the proper reagents. It must be borne in mind that woollen fibre contains nitrogen, and that it gives rise in itself to the formation of cyanide of potassium when treated as described 8 133. Hence, before evaporating the liquid and fusing the residue with carbonate of potassa, care must be taken to remove any particles of fibre which might be present. If a treatment of the stuff with alkaline water becomes necessary, but very little caustic potassa should be added, or, what is preferable, ammonia should be used instead of potassa. The reason for this is, that woollen fibre is soluble in potassa, but is not affected by ammonia. During the subsequent evaporation of the liquid, the ammonia passes off. It is absolutely necessary that an unstained piece of the cloth be treated in the same manner, for reasons above stated.

$ 137. Spots on wood, or stone, are carefully scraped off with a chisel, or a knife, then macerated in water, or alkaline water, and treated in the manabove described. Soil, impregnated with blood, is macerated in pure water, or in water containing potassa, or ammonia (Lassaigne, Pharm. Centralblatt. 1850. p. 365). Stains on iron are scraped off, and a small portion of it heated in a glass-tube, in order to produce the peculiar odor which is evolved on carbonizing animal matter; the residue may then be fused with carbonate of potassa. Another portion of the scraped off mass is macerated in water, or alkaline water. It is well known that iron-rust always contains some ammonia; hence, it becomes necessary to dry the mass thoroughly, in order to expel the ammonia, before fusing it with carbonate of potassa.

[blocks in formation]
« PreviousContinue »