was rendered opalescent, both by the pronitrate and pernitrate of mercury, but not by the third mercurial salt; but this third salt produced a slight opalescence in a solution of one part of muriatic acid in 3,552,000 parts of water.

3. Arsenic.--Some discussions have taken place in Germany respecting the best test for white arsenic. Gärtner observed that the formation of Scheele's green, by pouring cuprated ammonia into the liquid containing the white arsenic, does not in certain circumstances take place. Schweigger recommends sulphureted hydrogen, which is certainly a most delicate test of arsenic, in consequence of the fine yellow precipitate which it forms. The employment of nitrate of silver as a test for arsenic does not seem to be known in Germany. This test, first pointed out by Mr. Hume, but much simplified and improved by Dr. Marcet, is certainly very delicate ; and, when the precautions suggested by Dr. Marcet are attended to, does not seem liable to ambiguity.

4. Manganese.Pfaff has published a set of experiments on the method of separating manganese from iron, and has shown that all the methods hitherto proposed on the Continent are imperfect. Bergman's process has been long given up by all chemists." Vauquelin's, by means of bicarbonate of potash, he found likewise unsuccessful. The method by means of tartrate of potash is incomplete, because the tartrate of potash-and-manganese is soluble in water. Dr. John's method, by oxalate of ammonia, was like. wise unsuccessful. Nor did he succeed better by means of the succinates, benzoates, or phosphates. Mr. Hatchett's method of separating the iron, by means of ammonia, was not tried. I find that by means of it I can very easily procure perfectly pure oxide of manganese. Whether it would succeed equally in forming an accurate separation of manganese and iron for the purposes of analysis, I have not tried; though I think it probable that it might be used for that purpose with advantage, supposing iron and manganese to be the only substances in the solution upon which we operate.

5. Iron. Mr. Porrett has recommended triple prussiate of potash, or ferrureted chyazate of potash, as he calls it, as the best method of throwing down iron, and ascertaining its quantity. The precautions necessary to be attended to are the following. The ferrureted chyazite must be pure. There must be no excess of acid in the solution, or as little as possible. All other substances preci

, pitated by the ferrureted chyazate must be previously removed. The ferrureted chiyazate must not be added in excess, or as little so as possible. The solution being boiled, and the Prussian blue separated and weighed, every hundred parts of it must be considered as equivalent to 34.235 of peroxide of iron in the solution.

I have no doubt that when no manganese is present the ferrureted chyazate may be employed with considerable accuracy to detect the quantity of iron in any substance under analysis ; but as it most frequently happens in mineral analysis that iron and manganese are

mised together in unknown proportions, ferrureted ehvazate of potash cannot be employed in such cases till a good method is discovered of separating manganese from iron. Gehlen's method is the best hitherto proposed; though it only auswers when the whole of the iron is in the state of peroxide.

I may mention here, for the sake of our British marufacturers of sulphuric acid, that E. W. Martius announced in 1811, in a German journal, that he had found white arsenic in a glass carboy of English sulphuric acid. The arsenie had separated from the acid, and formed a crust in the inside of the glass. As the notice merely states the fact of the separation of white arsenic, I conceive it possible that Martius might have been mistaken. If his statement be accurate, the arsenic must have made its way into the carboy by some odd accident or other; for I think it hardly possible that it should have been mixed with the sulphur before its combustion.

VI. Aids. 1. Formic Acid. The reader is probably aware that this acid, which exists ready formed in red ants, was originally discovered by Ray and Fisher; ihat it was first accurately examined by Margraaf; that Arvidson and Oern published a very complete set of experiments on it in 1777. It continued to be considered as a peculiar acid till Fourcroy and Vauquelin published a set of experiments on it in 1803, and drew as a conclusion from them that it is not a peculiar acid, but a mixture of the acetic and malic acids. This dissertation convinced all the French chemists; and induced me in the second edition of my System of Chemistry to 'espunge it from the list of acids. But Suerzon having published a new set of experiments on it, in 1805, showed that the premises of the French chemists were insufficient to warrant their conclusions, and that formic acid possessed striking and 'essential properties which distinguished it from acetic acid. I suggested in my System the propriety of a more rigid examination of the formates than had hitherto taken place. This seems to have induced Gehlen to undertake a laborious set of experiments on the subject. He observes in the outset, that if I had been acquainted with the experiments of Arvidson and Oern, and of Richter, on the formules, I should probably have been satisfied, without requiring any farther proofs. Í regret that it has never been in my power to peruse either of the works alluded to by Gehlen. My knowledge of the experiments of Arvidson and Oern is derived from the account of them given by Keir in his Dictionary, and by Bergman in his Treatise on Elective Attractions. Gehlen's experiments are quite decisive; but they are, unfortunately, too long to be detailed here. He prepared, in the first place, formate of copper, from which he separated the formic acid by distilling it with sulphuric acid in à retort. He compared the pure förmic

acid thus obtained with acetic acid, procured from acetate of lead by a similar process.

tion

a

ate of

Jod is s bole

rers of

arbor

in the Dutice LEITE state o the ssible com

acid. ed hr

follows:

Thus prepared, it has an acid, and peculiar taste and smell, quite different from that of acetie acid.. When cooled down sufficiently, it becomes solid, but does not erystallize. Its specific gravity was 1•1168; and, when diluted with its own weight of water, the specific gravity becomes 1-060; and when with twice its weight of water, it becomes 1.0296. In all these respects acetic acid is very different. It likewise requires different proportions of bases to neutralize it. Gehlen describes minutely the formates of copper and barytes, and compares them with the acetates of the same bases. They differ in colour, solubility, form of crystals, and all their other properties, from each other.

2. Ferrureted Chyazic Acid.-Mr. Porrett has discovered two new acids, and rendered it probable that many more exist. Ferrureted chyazic acid is obtained from the salt formerly called triple prussiate of varytes. This salt is dissolved in water, and as much sulphuric acid added as is just sufficient to neutralize the harytes present. The mixture, being agitated in a phial, is set aside for some time. Sulphate of barytes precipitates, and the ferrureted chyazic acid remains in solution in the liquid. Its properties are as

It has a pale lemon colour; but no smell. It is decomposed by
a gentle heat, or by exposure to a strong light. Prússic acid is then
formed, and white triple prussiate of iron, which is soon changed
into Prussian blue. It separates acetic acid from all its combina-
tions, It combines with the different bases, and forms the salts
formerly called triple prussiates. This acid is composed of four
constituents ; namely, black oxide of iron, carbon, hydrogen, and
azote; or perhaps it would be as well to consider it as composed of
five constituents, oxygen, grön, carbon, hidrogen, and azote. It
would be a curious, but very difficult problem, to determine the
proportions in which these different constituents are united in this
complicated acid. How many atoms of each enters into it. From
the great permanency of this acid when compared with some of the
vegetable and animal acids, one would be disposed to suspect that
its composition is very simple. Perhaps an atom of each constituent
would not be very far from the truth.

According to Mr. Porrett, ferrureted chyazate of potash is com-
posed of
Black oxide of iron ...17.267

Ferrureted chyazic acid.. 47.66
Prussic acid.

..30-40 %
Potash

39.34 Water

13.00

100.00

are, the

This analysis cannot be reconciled with the supposition of ferrureted chyazic acid beirg a compound of an atom of each of its constituents. If we suppose the salt composed of an atom of acid and an atom of base, as is usual with the salts of potash, then an

atom of the acid would weigh only 7.268, which is considerably
less than an atom of each of the constituents, which together
weigh 10.829. If, on the other hand, we take the proportion of
black oxide of iron and prussic acid as a criterion, the atom of acid
ought to weigh 22.485, and it might be a compound of one iron
+ one oxygen + six carbon + five azote + six hydrogen ; besides
which many other numbers might be chosen. These anomalies
render Mr. Porrett's analysis of the ferrureted chyazate of potash
somewhat doubtful.
Ferrureted chyazate of barytes he found composed of
Ferrureted chyazic acid

34:31
Barytes ...

49.10 Water

16:59

100.00

Ferrureted chyazate of iron is composed of
Black oxide of iron..19:33 } Ferrureted chyazic acid.. 53•380
Prussic acid......

....34.05 Peroxide of iron

34:235 Water....

12:385

.

100.000

success.

a

3. Sulphureted Chyazic Acid.~Mr. Porrett discovered this acid in 1808, by boiling three or four parts of Prussian blue in powder with one part of sulphuret of potash, and a sufficient quantity of water. The new acid is gradually formed, and neutralizes the potash in the solution. Various other processes were attended with

To obtain the acid from this solution in a state of purity, Mr. Porrett employed the following method :- Add sulphuric acid till the liquid acquires a decidedly sour taste : then keep it for some time nearly at the boiling point. When cold, add to it a little black oxide of manganese, which will turn it to a beautiful crimson colour. Filter the liquid, and add to it a solution containing two parts of sulphate of copper and three parts of prosulphate of iron, till the crimson colour disappears. A copious white precipitate falls, composed of protoxide of copper combined with sulphureted chyazic acid. Boil the precipitate in a solution of potash, which separates the acid, and leaves the oxide of copper. Mix the potash solution with sulphuric acid, and distil. The sulphureted chyazic acid comes over into the reservoir. It is still mixed with some sulphuric acid, from which it may be freed by carbonate of barytes.

The acid thus obtained is colourless, has a strong smell, analogous to that of acetic acid, and its specific gravity is 1.022. At a boiling temperature it dissolves a little sulphur. This acid consists of twothirds of its weight of sulphur and one-third of the constituents of prussic acid. The salts which it forms have the following -properties :

a

4,

а

considerably

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proportioad

atom of achi

a

se anomalis te of potat

Sulphureted chyazate of potash : a deliquescent salt, soluble in alcohol.

of soda : ditto, crystallizes in rhombs.

of lime: ditto, soluble in alcohol, from which it may be obtained in needle-form crystals.

of ammonia: ditto, not crystallizable.

of magnesia : ditto, when dried has a mica. ceous appearance.

of alumina : crystallizes in octahedra, which do not deliquesce.

of barytes : a deliquescent salt, crystallizing in long slender prisms of a brilliant white. It is

composed of Sulphureted chyazic acid .....

30.1 Barytes

69.9

of

31 -10 -59

00

100.0

.. 53-380

.. 34:23 .. 12385

100.000

ered this ac ne in ponde

t quantity utralizes tik ttended with te of puri

Iphuric as p it for som

to it a litt tiful crime ptaining hate of irok cipitate fal reted cha

of strontian : a deliquescent salt, crystallizing in long slender prisms in groups radiating like zeolite.

of silver: a white insoluble powder.
of mercury: a white insoluble powder.

of potash and prussiate of mercury: a brilliant silvery lustre; very soluble in hot, and little soluble in cold, water.

of protoxide of copper: a white powder, insoluble in water. Its constituents are, Sulphureted chyazic acid

36.855 Protoxide of copper

63.145

100.000 of peroxide of copper : a bright pea-green liquid.

- of protoxide of lead : a soluble salt in obtuse rhombs.

of protoxide of iron : a colourless and very soluble salt.

of peroxide of iron : a beautiful crimson

salt, very deliquescent. The sulphureted chyazates of tin, bismuth, manganese, zinc, cobalt, nickel, palladium, uranium, molybdenum, and chromium, are very soluble.

4, Fuming Sulphuric Acid.The singular qualities of the fuming sulphuric acid manufactured at Nordhausen, in Germany, from green vitriol, have long attracted the attention of chemists, and various solutions of the anomalies which it presents have been given. Fourcroy's explanation of it, by affirming that it is a mixture of sulphuric and sulphurous acids, bias been pretty generally

Ich separat

tash soluti:

c acid come

phuric aci

At a bailar

71
, analone

boilig sists of the nstituents a lowing-pon

a