Legal Chemistry / A Guide to the Detection of Poisons, Examination of Tea, Stains, Etc., as Applied to Chemical Jurisprudence

Legal Chemistry / A Guide to the Detection of Poisons, Examination of Tea, Stains, Etc., as Applied to Chemical Jurisprudence

Alfred Naquet
Alfred Naquet

Author: Naquet, Alfred, 1834-1916
Legal Chemistry
A Guide to the Detection of Poisons, Examination of Tea, Stains, Etc., as Applied to Chemical Jurisprudence

Legal Chemistry.

Professor to the Faculty of Medicine of Paris.
J. P. BATTERSHALL, Nat. Sc. D., F.C.S.
NEW YORK: D. VAN NOSTRAND, Publisher, 23 Murray Street and 27 Warren Street.
Transcriber’s Note: Obvious printer errors have been corrected. A list of all other changes can be found at the end of the document. In the Appendix of the book, only the most obvious errors of punctuation were remedied.
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The importance of exact chemical analysis in a great variety of cases which come before the courts is now fully recognized, and the translation of this excellent little book on Legal Chemistry, by one of the most distinguished French Chemists, will be appreciated by a large class of American readers who are not able to consult the original. While it is to be regretted that the author has not presented a much more complete work, there is an advantage in the compact form of this treatise which compensates, in some degree, for its brevity.
The translator has greatly increased the value of the book by a few additions and his copious index, and especially by the lists of works and memoirs which he has appended; and while he could have further increased its value by additions from other authors, we recognize the weight of the considerations which induced him to present it in the form given to it by the author. Some chapters will have very little value in this country at this day, but the translator could not, with propriety, omit anything contained in the original.
C. F. Chandler.
The principal change to note in this edition of the Legal Chemistry is the addition of a chapter on Tea and its Adulteration. The general interest at present evinced concerning this species of sophistication appeared to call for a simple and concise method of examination which would include the requisite tests without entering upon an exhaustive treatment of the subject. The translator’s practical experience in the testing of tea at the United States Laboratory of this city has enabled him to make a few suggestions in this regard which, he trusts, may be of use to those interested in food-analysis. Numerous additions have also been made to the bibliographical appendix.
J. P. B.


Introduction 5
Methods of Destruction of the Organic Substances  
By means of Nitric Acid 8
  ”   ”    Sulphuric Acid 9
  ”   ”    Nitrate of Potassa 10
  ”   ”    Potassa and Nitrate of Lime 12
  ”   ”    Potassa and Nitric Acid 12
  ”   ”    Chlorate of Potassa 13
  ”   ”    Chlorine 13
  ”   ”    Aqua Regia 14
Dialysis 15
Detection of Poisons, the presence of which is suspected.
Detection of Arsenic 17
Method used prior to Marsh’s test 17
Marsh’s test 21
Raspail’s test 29
Reinsch’s test 30
Detection of Antimony 30
Flandin and Danger’s apparatus 32
Naquet’s apparatus 34
Detection of Mercury 36
Smithson’s pile 36
Flandin and Danger’s apparatus 37
Detection of Phosphorus 39
Orfila’s method 39
Mistcherlich’s method 40
Dusart’s method, as modified by Blondlot 40
Fresenius and Neubauer’s method 42
Detection of Phosphorus by means of bisulphide of carbon 43
Detection of Phosphorous Acid 45
Estimation of Phosphorus 45
Detection of Acids 46
Hydrochloric Acid 46
Nitric   “ 47
Sulphuric Acid 47
Phosphoric   “ 48
Oxalic   “ 49
Acetic   “ 49
Hydrocyanic   “ 50
Detection of alkalies and alkaline earths 52
Detection of chlorine, bromine and iodine 54
Chlorine and Bleaching Chlorides 54
Bromine 55
Iodine 56
Detection of Metals 56
Detection of alkaloids and some ill-defined organic substances 65
Stas’s method 65
  ”   ”    as modified by Otto 69
  ”   ”   ”   ”   Uslar and Erdman 70
Rodgers and Girdwood’s method 71
Prollius’s method 72
Graham and Hofman’s method 73
Application of Dialysis in the detection of Alkaloids 74
Identification of the Alkaloid 74
Identification of Digitaline, Picrotoxine and Colchicine 80
Method to be employed when no clew to the nature of the Poison present can be obtained 85
Indicative tests 86
Determinative tests 94
Miscellaneous Examinations 96
Determination of the nature and color of the hair and beard 96
Determination of the color of the hair and beard 96
Determination of the nature of the hair 99
Examination of Fire-arms 100
The gun is provided with a flint-lock and was charged with ordinary powder 100
The gun is not provided with a flint-lock 103
Detection of human remains in the ashes of a fire-place 104
Examination of writings 105
Examination of writings, in cases where a sympathetic ink has been used 110
Falsification of coins and alloys 112
Examination of alimentary and pharmaceutical substances 114
Flour and Bread 114
Fixed Oils 128
a Olive Oil intended for table use 128
b Olive Oil intended for manufacturing purposes 130
c Hempseed Oil 130
Tea 130
Milk 137
Wine 142
Vinegar 147
Sulphate of Quinine 148
Examination of blood stains 150
Examination of spermatic stains 158
Appendix 163
Books of Toxicology, etc. 163
Memoirs on Toxicology, etc. 168
Index 187

The term Legal Chemistry is applied to that branch of the science which has for its office the solution of problems proposed in the interest of Justice. These most frequently relate to cases of poisoning. When the subject of the symptoms or anatomical lesions produced by the reception of a poison is under consideration, the services of a medical expert are resorted to; but when the presence or absence of a poison in the organs of a body, in the egesta of an invalid or elsewhere is to be demonstrated, recourse is had to the legal chemist. Investigations of this character require great practice in manipulation, and, however well the methods of analysis may be described in the works on the subject, there would be great danger of committing errors were the examination executed by an inexperienced person. The detection of poisons, although perhaps the most important, is not the only subject that may come within the province of the legal chemist; indeed, it would be somewhat difficult to define, a priori, the multitude of questions that might arise. In addition to cases of supposed poisoning, the following researches are most often required:
1. The examination of fire-arms.
2. The analysis of ashes, in cases where the destruction of a human body is suspected.
3. The detection of alteration of writings, and of falsification of coins and precious alloys.
4. The analysis of alimentary substances.
5. The examination of stains produced by blood and by the spermatic fluid.
Each of these researches justly demands a more extended consideration than the limits of this work would permit. The several subjects will be treated as briefly as possible, and at the same time, so as to convey an exact idea of the methods employed, leaving to the expert the selection of the particular one adapted to the case under investigation. We will first mention the methods used in the search for toxical substances. The poisons employed for criminal purposes are sometimes met with in a free state, either in the stomach or intestines of the deceased person, or in the bottles discovered in the room of the criminal or the victim. Under these circumstances, it is only necessary to establish their identity by means of their chemical properties, as directed in the general treatises on chemistry, or by their botanical, or zoological character, in case a vegetable or animal poison, such as cantharides, has been administered. Examinations of this class are extremely simple, the analysis of the substances found, confined to a few characteristic reactions, being a matter of no great difficulty. We will not here dwell longer upon this subject, inasmuch as the analytical methods used are identical with those employed in more complicated cases, with the sole difference that, instead of performing minute and laborious operations in order to extract the poisons from the organs in which they are contained, with a view of their subsequent identification, we proceed at once to establish their identity. The directions given in regard to complicated investigations apply, therefore, equally well to cases of a more simple nature. The detection of a poison mixed with the organic substances encountered in the stomach, or absorbed by, and intimately united with the tissues of the various organs is more difficult. If, however, other information than chemical can be obtained, indicating the poison supposed to be present, and the presence or absence of this one poison is the only thing to be determined, positive methods exist which admit of a speedy solution of the question. When, on the other hand, the chemical expert has not the advantage of extraneous information, but is simply asked,—whether the case be one of poisoning?—nothing being specified as to the nature of the poison used, the difficulty of his task is greatly increased. Up to the present time, the works on Toxicology have, it is true, given excellent special tests for the detection of particular poisons; but none have contained a reliable general method, which the chemical expert could use with the certainty of omitting nothing. Impressed with this need, we proposed, in 1859, in an inaugural dissertation then presented to the Faculty of Medicine, a general method, which, after some slight modifications, is now reproduced. The special methods which allow of the detection of various individual poisons will, however, first be indicated. In cases where the poison is mixed with organic matter, the latter must be removed as the first step in the investigation, as otherwise the reactions characteristic of the poison searched for would be obscured. When the poison itself is an organic substance, this separation is effected by processes modified according to the circumstances. If the detection or isolation of a metallic poison is to be accomplished, the most simple method consists in the destruction of the organic substances. The various methods for effecting this decomposition will now be described.



In order to destroy the organic matters by this process, a quantity of nitric acid equal to one and a half times the weight of the substances taken is heated in a porcelain evaporating dish, the amount of acid being increased to four or six times that of the organic substances if these comprise the brains or liver. As soon as the acid becomes warm, the suspected organs, which have previously been cut into pieces, are added in successive portions: the organs become rapidly disintegrated, brownish-red vapors being evolved. When all is brought into solution, the evaporation is completed and the carbonaceous residue obtained separated from the dish and treated either with water, or with water acidulated with nitric acid, according to the nature of the poison supposed to be present.
Several objections to this method exist, the most serious of which is based upon the fact that the carbonaceous residue, containing, as it may, nitric acid, readily takes fire and may therefore be consumed, or projected from the vessel. This objection is a grave one, and is not always entirely removed by the continual stirring of the materials. According to M. Filhol, the addition of 10 to 15 drops of sulphuric acid to the nitric acid taken obviates the difficulty; not having personally tested the question we cannot pronounce upon it. If it be the case, this process is an advantageous one, as it is not limited in its application, but can be used in the separation of all mineral poisons.


The organic matter to be decomposed is heated with about one-fifth of its weight of concentrated sulphuric acid, the complete solution of the materials being thus accomplished. The excess of acid is next removed by heating until a spongy carbonaceous mass remains. The further treatment of this residue depends upon the nature of the poison supposed to be present. If the sulphate of the suspected poison is a soluble and stable compound, the residue is directly treated with water; if, on the contrary, there is reason to think that the sulphate has suffered decomposition, the mass is taken up with dilute nitric acid; if, finally, the presence of arsenic is suspected, the residue is moistened with nitric acid, in order to convert this body into arsenic acid. The acid is afterwards removed by evaporation, the well pulverized residue boiled with distilled water, and the solution then filtered.
This method, when applied in the detection of arsenic, is objectionable in that the carbonaceous residue, in contact with sulphuric acid, almost invariably contains sulphurous acid, detected by means of permanganate of potassa. This acid, being reduced in the presence of hydrogen, would cause the formation of insoluble sulphide of arsenic, and in this way prevent the detection of small amounts of arsenic by the use of Marsh’s apparatus. M. Gaultier de Claubry, indeed, states that he has not been able to detect the presence of sulphurous acid in the carbonaceous residue; but one affirmative result would, in this case, outweigh twenty negative experiments. A further objection to this process consists in the fact that the materials to be destroyed almost always contain chlorides, which, in presence of sulphuric acid and an arsenical compound, might determine the formation of chloride of arsenic, a volatile body, and therefore one easily lost. This difficulty is doubtless of a less serious nature than the preceding, as the operation can be performed in a closed vessel provided with a receiver which admits of the condensation of the evolved vapors; but even then the process would be prolonged. The above method is still again objectionable on account of its too limited application, it being serviceable almost exclusively in cases where the poisoning has been caused by arsenic, for, if applied in other instances, a subsequent treatment would be necessary in order to redissolve the metal separated from its decomposed sulphate.


This method was formerly executed as follows: Nitrate of potassa was fused in a crucible, and the substances to be destroyed added in small portions to the fused mass. The organic matter soon acquired a pure white color; owing, however, to the imperfect a

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