You ask me to examine what Gay-Lussac has advanced respecting the nitrous gas eudiometer, and to repeat the experiments on which his method is founded, because they are in opposition to my views relative to nitric and nitrous acids. I acknowledge that I feel no inclination to undertake such a task. I am always averse to disputes; and if I were to engage in one, it must be of such a nature that it could be fully resolved by experiment. This is not the case with Gay-Lussac's experiments. Dalton has already shown, with tolerable accuracy, that according as there is an excess of nitrous or oxygen gas, a maximum or minimum of nitrous gas will be absorbed, both measured by the quantity of oxygen gas which is likewise absorbed. On this maximum or minimum usually depends the formation of pure nitric or nitrous acid. The question, therefore, comes to this: whether between these two points there are gradations, consisting of combinations of determinate proportions of nitric and nitrous acids, or not; and likewise whether the results of Gay-Lussac be those which he really obtained, or whether he did not correct them by his views of true theory. The solution of these questions is attended with too much difficulty for me to bestow upon them the time that would be required for their examination.

M. Avogrado's remarks upon my electro-chemical theory I have already read in the Annales de Chimie. He appears not to know the treatise on the chemical action of the electrical pile by Hisinger and myself. His remarks upon my use of the terms electro-positive and electro-negative are correct. They had been already anticipated in your Annals, on occasion of my experiments and those of Davy. I had changed them for others long before Avogrado's paper appeared, as may be seen from my papers published in England. Some additions to the electro-chemical theory, which these papers contain, and which hitherto are unknown both in Germany and France, are perhaps worthy of your attention. You will find them in my treatise on the Cause of Chemical Proportions.

Van Mons has communicated to me the discovery that he has decomposed the fluates at a red heat by means of hydrogen, and obtained compounds of fluoric acids and metals destitute of oxygen. Certainly this is strange. It ought likewise to be inaccurate, according to his preconceived opinions. Has he obtained a fluoric oxide, or a compound of fluoricum with metals? Had he given me the names of the salts on which he made his experiments, it would have been easy to have investigated the subject. But I must wait for a more accurate account of his experiments, which he has promised me, before I can repeat them.

You say to me that different persons wish that I would give an example how I make accurate chemical analyses on a small scale. This would be a difficult task; for I believe that I possess no other method or greater dexterity than other chemists. I seldom work upon a small scale. Most of my analyses are performed with ten or five grammes, that is to say, with 160 or 80 Nurnberg medicinal grains (154.44 and 77.22 grains troy); and this I believe is the best

quantity for chemical analyses. The difficulty is increased when either much more or much less is employed. In all my analyses I have this rule before my eyes: "Endeavour to find a method of analysis so that the accuracy depends as little as possible upon the manual dexterity of the operator. When this is found, consider what unavoidable circumstances intervene to render the results inaccurate, and whether by their means the quantities obtained are increased or diminished. Then make a second analysis, in which all these circumstances act in a way directly contrary. If the results agree, the experiment is accurate." For example, you will find in my analysis of red oxide of iron that in one of my experiments I dissolved the iron in a weighed glass capsule, evaporated the solution, and exposed the oxide to a red heat. Here no loss was pos sible. In a second experiment I dissolved the iron in aqua regia, precipitated it by ammonia, washed the oxide upon a weighed filter, and exposed it to a red heat. Here no increase was possible; nothing but a diminution could take place. But both experiments gave the same results. Hence I concluded that in the first experiment no increase of weight had taken place, from the impurity of the acid, or the corrosion of the glass; and that in the second no remarkable loss had been sustained, in consequence of the inaccuracy of the method followed. By these perpetual checks I have learnt to look for, and to avoid, sources of inaccuracy. I have pointed out several of these sources in my manual of chemistry under the article inorganic substances. Still, however, a good deal depends upon manual dexterity and long practice; so that it is as impossible to make an accurate chemist by written directions as it is for one artist to make another a consummate tradesman by mere written rules. A clever student of chemistry might perhaps learn from me to attend to several small particulars, which he might not of himself remark, and yet are of importance.

But my letter is already too long.

BERZELIUS.

ARTICLE X.

-Astronomical and Magnetical Observations at Hackney Wick. By Col. Beaufoy.

Latitude, 51° 32′ 40-3" North. Longitude West in Time 6"

June 10, Occultation of Cancri Immersion.... 9h 26' 11" Mean Time at by the moon ....

Emersion

....

10

9 34 H. W.

June 11, Emersion of Jupiter's 11h 33′ 19′′ Mean Time at Hackney Wick,

Ditto at Greenwich,

There appears to be a singular increase of the variation in the month of April, more particularly so in May and June. Suspecting there might be some error, the source of which was in the instrument, but which I could not discover, I sent it to the maker, Mr. Dollond, who examined it, sharpened the point of suspension, and placed new agates in the needles, which alterations do not seem to have affected the result of the observations. May it not therefore be justly inferred that the increase is real, and not apparent? One circumstance is indubitable, which is, that the vibration of the needle has been seldom, and of small extent, since the 20th of February last, on which day the needle vibrated between 28 and 29 minutes.

ท

The immersion and emersion of Cancri was instantaneous, and no diminution of the star's light was perceptible.

The dew which fell on the instrument rendered the observation on the 11th inst. doubtful to a few seconds.

Rain fallen Between noon of the 1st June

Between noon of the 1st May 1-131 inch.

Evaporation during the same period

.2.70

ARTICLE XI.

Recovery of the Aachen Mass of Native Iron. In a letter from Dr. Benzenberg.*

Kloster Brüggen, near Crefeld, Dec. 15, 1814. You will already know that the great mass of native iron at Aachen, which had been lost, has been lately again found. I went last week to Aachen to see it, and can give you the following information respecting it.

In the year 1762 Councellor Löber was with Maximilian Prince of Saxony at the baths of Aachen, as his physician. At the time they inhabited the house called Büchel, at the new bath. Löber observed in the pavement an uncommonly large iron-stone. He requested liberty to dig it up, obtained it, and took some specimens of it. He gave some of the smallest to the physician Dr. Kretschmann, in Dresden, whose collection of minerals came into the possession of the University of Wittenberg. This information is to be found in the Wittenberg Weekly Paper for 1773, page 36; from which it found its way into he Memoirs of the Berlin Natural History Society, vol. vii. page 323. By a mistake of the writer in both accounts, Aken is substituted for Aachen; and Chladni, who mentions this mass of iron in his well-known treatise, considers the place as Aken in Magdeburg. Letters were written to Aken on the

* Translated from Gilbert's Annalen der Physik for Dec. 1814, vol. xlviii. p. 410.

subject; but there they knew of no mass of iron whatever. It was then referred to Aachen, in another paper which appeared in 1804, on native iron. Probably the mistake was discovered by the reference to the baths in the original paper.

In the year 1812 Dr. Chladni wrote to the Consistorial President, Frederick Jakobi, at Aachen, requesting information respecting this mass of iron. As Dr. Lesoinne could give no intelligence respecting it, he and apothecary Monheim applied to the old town secretary, Couver. He recollected the digging up of the mass in 1762, and that some pieces had been struck off, and deposited in the town-house, but had been soon after lost. The mass, he said, had been again deposited in the place from which it had been dug, and the surface again plastered over. Fourteen days after this information Couver died, at the age of 78.

Mr. Monheim gave this information to Trommsdorf, who published it in his journal in 1812. Professor Weiss, in Berlin, endeavoured to interest the Academy in the re-discovery of this mass of iron in a town which belonged to the general government of Prussia. In consequence an order was obtained from the Chancellor Prince Hardenberg to the Governor-General Sack to fulfil the wishes of the Academy.

The plaster being again removed, and the bottom examined for several days, the mass of iron was at last found, dug up amidst a crowd of people, and brought into the court of Mr. Biergans, Director of the Circle, where it lies at present.

It is covered with iron ochre, and, like all similar masses, is of an irregular shape, approaching to the oval. Its length is four feet nine inches; its breadth, two feet eleven inches; and its thickness two feet six inches; and its specific gravity, determined by a piece struck off from it, is 67. The whole weight amounts to about 10,000 lbs., supposing we reduce the size to or in order to convert it into a parallelogram. The coating of ochre is half a line thick. Under it there lies a kind of bark half an inch thick, which may be easily separated from the stone. It is greenish, vesicular, and exhibits the marks of fire. Under this covering lies the native iron. It is extremely tough. In breaking off a few specimens, no fewer than eight chissels were broken. Mr. Monheim, a pupil of Vauquelin, has not yet finished his analysis of it; but he has ascertained that it contains no nickel, but is composed of about arsenic and iron. Perhaps also there may be a third metal; but it is in so small quantity that Mr. Monheim has not yet determined its nature.*

How this mass has come to Aachen, we have no information.

According to the statement of Löber, the weight of this mass of iron was between 15,000 and 17,000 lbs., and it was covered with a coating from an half to one inch in thickness. It was malleable, and could be hardened and polished like the best English steel. Klaproth found no nickel in the 300 lbs. of native iron found at Villa, on the Collina di Brianza; but in the 130 lbs. from Ellnbogen he found 2.5 per cent, of nickel.-GILBERT.