mentor, M. Signoret, has, according to his assertion, far exceeded this. He states, that he has obtained stains when the arsenic formed only the

1

20,000,000 part of the supposing the liquid

liquid employed. In this case again, to be pure water, the arsenic present would be nearly in the proportion of 1 grain to 285 gallons of water. It appears to me, however, that this statement requires further confirmation. In some experiments made by Mr. Taylor, it would appear, that he obtained slight brown annular stains with the 1080th part of a grain of arsenic. The amount of dilution in that case was equal to 1,000,0 with the 720th part of a grain, on the dilution being equal to 800,000, the stains were much more decided-with grain the dilution being equal to 48,000, stains were produced, sufficiently characteristic to be safely relied upon in legal medicine.

10

1

1

100

From experiments which I have made, about 100 of a grain in 5 fluid oz. of liquid, which, considering it as pure water, would give a dilution equal to 218,750, yielded 60 distinct stains on porcelain, and 12 indistinct stains. In another experiment, grain of arsenic was mixed with 2 fluid oz. of chocolate containing cream and sugar, the organic matter was destroyed by nitric acid, and the residue placed in the hydrogen apparatus, with 5 fluid oz. of liquid, being a dilution equal to 21,875, supposing the liquid to be pure water, distinct films were obtained, 85 in number, and about 12 indistinct stains. In all the above experiments, the degree of dilution is calculated upon the supposition that the liquid was pure water, but in truth, water and sulphuric acid were used, and as the latter is much heavier than the former, the relative weight of the arsenic and liquid would be even less than the quantities specified.

I shall conclude what I have to say on this subject by directing your attention to a test of reduction which has

F

been recommended still more recently than Marsh's test― I mean Reinsch's test. This test depends upon the fact, that white arsenic and certain preparations of that substance, when boiled in water with bright copper and muriatic acid, give a coating of metallic arsenic to the copper, which coating, when heated in a tube, yields characteristic crystals of arsenious acid by sublimation. This test is one which enables us to pronounce with certainty as to the presence of arsenic by an estimation of only three of its properties. "There is no substance in nature with which we are acquainted, capable of causing a bluish stain upon copper, or in some cases, where the quantity is more considerable, an iron gray coating, and which, when heated in a glass tube by a spirit lamp, gives a sublimate of colourless resplendant octohedral crystals, soluble in water and precipitable yellow by ammoniacal nitrate of silver, the precipitate becoming of a dirty red colour by exposure to light, excepting Arsenic."

It may be observed, that when the quantity operated upon is very small, the white sublimate does not manifest a distinct crystalline form, but even then it will in most cases allow of the peculiar reaction of the ammoniacal nitrate of silver. Two only of the properties above mentioned cannot be considered as sufficient for the demonstration, because antimony and quicksilver can be deposited upon copper under like circumstances. And with regard to the former metal,-when in small quantity, the stain it produces upon copper is very like that resulting from arsenic. In no case, however, as far as my own experiments go, can any decided well-developed white crust be obtained, from an antimonial stain. You may, indeed, by the application of a strong heat produce a small white deposit above that part of the tube where the coated copper has been placed. This spurious sublimate, however, is not soluble in water, and

cannot produce ammoniacal nitrate with silver, the peculiar reaction due to the true arsenical sublimate. In concluding, allow me to lay before the Society, a few experiments which I have made, for the purpose of shewing the delicacy of Reinsch's test, and its applicability to organic mixtures:—

Experiment 1st.-2 drops of a solution of arsenious acid in water=.02 grain were mixed with 1 drachm of water and muriatic acid, and 3 slips of copper were stained as soon as the liquid boiled. In this case, taking the quantity of arsenic as unity, and supposing the liquid water, the degree of dilution will be equal to 2785.

Experiment 2nd.-1 drop of the solution=.01 grain of arsenic was mixed with 1 drachm of water and acid, and three slips of copper, they were stained as soon as the fluid fully boiled; when the liquid was reduced to, the slips were removed, dried and heated in a tube, a distinct white crystalline sublimate was obtained. The degree of dilution, in this case, supposing the liquid water, was in the first place, equal to 5470; when the copper was removed, it was equal to 1867.

Experiment 3d.-1 drop of the solution = .01 grain of arsenious acid was mixed with water and muriatic acid, 4 square inches of copper surface were fully coated; these, when heated in a tube, yielded a distinct white chrystalline sublimate, giving a yellow precipitate when dissolved in water and mixed with ammoniacal nitrate of silver, the quantity of metallic arsenic in this case was, and this small quantity was diffused over 4 square inches of copper surface.

Experiment 4th.- grain of arsenious acid was mixed with 1 oz. bread, 4 drachms water, and some muriatic acid. Three copper slips were stained before the water was evaporated off; when the water was evaporated off, the copper slips had a dark iron grey coating throughout: these were removed and 4 fresh slips introduced, the fluid was evaporated to a syrupy consistence, when the copper came out nearly as much stained as the first set.

auxiliary evidence for the "Nebular hypothesis," while, on the contrary, opposing facts are numerous. In Geology, too, it was contended that recent investigations had completely overturned the views which the author of the Vestiges" propounded; and therefore, that while his work was interesting in many respects as a book, it was utterly unworthy of any place among treatises on scientific subjects.

SEVENTH MEETING.

ROYAL INSTITUTION, January 27th, 1845.

JOS. B. YATES, Esq., PRESIDENT, in the Chair.

The SECRETARY read an account, by Dr. WATSON, of a visit made by several Members of the Society to a human body lately disinterred from the guano at Ichaboe. It was brought to Liverpool in the ship Colchester, Capt. Withers. From some writing carved on the stave of a barrel, it appeared to have been buried in 1791; and as it was found about seven feet below the surface, and would, probably, be buried at a depth of about three feet, some idea may be formed of the rate of deposition of the guano. The chief point of interest was, that a human body has thus been preserved by a process of mummification, no less singular than perfect; adding another instance to the records of forensic medicine, of the effect of animal ordures in retarding the process of decomposition

THE APPOINTED BUSINESS FOR THE EVENING WAS,

ADJOURNED DISCUSSION ON THE THEORY ADVANCED IN "VESTIGES, &c."

The Rev. J. ROBBERDS, B.A., as the mover of the adjournment, introduced the subject by reading a few general observations, the purport of which was that some of the criticisms in the paper of the previous evening, especially those connected with the Nebular hypothesis, admitted of