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ART. XVII.-Upon a peculiar kind of Isomorphism that plays an important part in the Mineral Kingdom; by Professor SCHEERER of Christiania.

(Continued from p. 73.)

II. BORATES.

1. Datholite.

NONE of the prior formulæ for datholite agree so well with its composition as that brought forward by Rammelsberg, namely, 2Ca3 Si+B3 Si2 +3.

This formula, however, involves the improbability that the boracic acid is here viewed in the light of a base combined with the silica. This improbability may however be got over by writing the formula as follows: 3[Ca Si+Ca R]+(R) Si, wherein therefore, (R)=3H.

2. Botryolite.

Rammelsberg's formula for this mineral is,

2Ca' Si+B Si+6 H,

which admits of conversion to 3[Ca Si+Ca B]+(R)2 Si.

III. PHOSPHATES.

A. Phosphates of Iron.

1. Vivianite.

According to Stromeyer's analysis, the vivianite of St. Agnes in Cornwall, consists of phosphoric acid 31-8125, protoxyd of iron 41-2266, water 27 484399-8934.

Hitherto all endeavors have been in vain to arrive at a formula that would represent in a satisfactory manner the results of this analysis by so celebrated an analyst as Stromeyer, and which was apparently conducted with such precision. Von Kobell's formula, which gives the closest approximation to the result, Fe3 P+8H, requires a composition of phosphoric acid 28-69, protoxyd of iron 42:38, water 28.93 100.00.

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This differs not immaterially from the result of the analysis, and moreover involves a ratio in the quantity of oxygen contained in the base, the acid and the water, which in a compound of so little complicated a nature can hardly be looked upon as probOn calculating the water in Stromeyer's result as a base isomorphous with protoxyd of iron (3H=1Fe) which, after the SECOND SERIES, Vol. VI, No. 17.-Sept., 1848.

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number of proofs we have adduced thereof, we are fully borne out

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in doing, we obtain an oxygen ratio of 17·47 P : 17·53 (Fe), responding with almost mathematical accuracy to the simple formula (Fe) P, and in which formula base and acid contain equal amounts of oxygen.

2. Earthy Vivianite, from Hillentrup.

This consists, according to an analysis of Brandes, of phosphoric acid 30-320, protoxyd of iron 43.775, water 25-000, alumina 0.700, silica 0·025=99-820.

The oxygen ratio deduced herefrom is as follows: 18.60: 17:38. Deducting the alumina as a phosphate, the ratio becomes even more nearly 1 1, whence we also obtain for this mineral too the formula (Fe) P.

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3. Vivianite, from Bodenmais.

Vogel's analysis gave, phosphoric acid 26-4, protoxyd of iron 41.0, water 31.0=98.4.

If we may rely on the accuracy of this result, it will justify

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the following formula, (Fe)5 P+5H.

The oxygen ratio as it may be calculated from the result of the analysis, is, 14-79P: 14-00(Fe): 13.58H

should be

14:00 14:00 : 14.00.

A portion of the water in this mineral is basic, another portion exists as a hydrate. The formula thus resulting for the Bodenmais vivianite, is precisely similar to that which we obtain upon converting, on the principle here involved, the formula of the artificially prepared hydrous phosphate of magnesia, which is Mg2 P+14H, whereby we obtain (Mg) P+5H.

The corresponding artificial salts of the protoxyd of iron and of the protoxyd of manganese, have not as yet been analyzed, but without a doubt the same formula is also applicable to them. It would however be well to submit the Bodenmais vivianite to a further examination in order to ascertain with certainty whether in point of fact its composition is different from that from Cornwall, which as the two minerals agree in their crystalline form is certainly not probable.

4. Mullicite.

Thompson obtained for the composition of this mineral, phosphoric acid 26.06, protoxyd of iron 46 31, water 27.14-99-51. The corresponding oxygen ratio is, 14-60 P: 14:00 (Fe): 13.75, which gives as the formula of mullicite (Fe) P+5H,

agreeing with Vogel's analysis of the Bodenmais vivianite. The chemical difference between both minerals would consist therefore merely herein, that in the former a smaller quantity of the protoxyd of iron is replaced by water than in the latter.

5. Vivianite from the Mauritius.

According to the analysis of Laugier it consists of phosphoric acid 21, protoxyd of iron 45, water 34 100.

From these numbers we can, it is true, surmise no great accuracy, nevertheless they afford an oxygen ratio of 11-77 P: 10-25 Fe: 30-11, corresponding approximately to the formula Fe3 P+15H, according to which the oxygen ratio should be 10 10 30. In this mineral, therefore, the whole of the water appears to exist as a hydrate. The formula however admits of being thus written, (Fe) P, in which case the whole of the water figures as basic.

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B. Phosphates of Copper.

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As oxyd of copper is not isomorphous with magnesia, protoxyd of iron, &c., it of course cannot be assumed that three atoms of water replace one atom of oxyd of copper. From grounds which I will afterwards explain, there is more than a probability that two atoms of water can replace one of oxyd of copper. That less water should be required to replace one atom of oxyd of copper than one atom of magnesia, is sufficiently substantiated by the different basic qualities of these compounds. In calculating the oxygen ratio of the following phosphates and arseniates of copper, it is assumed, as yet hypothetically, that 2=1Cu.

1. Libethenite.

The crystallized Libethenite consists, according to Berthier's analysis, of phosphoric acid 287, oxyd of copper 63.9, water 7.4 1000. This gives, upon the above supposition, an oxygen ratio of 16·08P: 16·18(Cu), corresponding exactly to the formula (Cu) P, which is the formula of the Cornwall vivianite and of the eathy vivianite from Hillentrup.

2. Phosphorochalcite.

Rammelsberg calculated from Lynn's analysis of the phosphorochalcite from Rheinbreitenbach, the formula Cu3 P+5H, coinciding completely with the formula here adduced for the phosphates. According to the analysis perhaps a portion (though for a certainty but a very small one) of the oxyd of copper may

be replaced by water, and the formula in consequence becomes (Cu) P+5H, agreeing with the Bodenmais vivianite and mullicite.

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3. Phosphate of Copper, from Ehl, near Rheinbreitenbach. This consists, according to Bergmann, of phosphoric acid 24.93, oxyd of copper 65.99, water 9.06 99.98, corresponding to the oxygen ratio 13.99 P: 13-31 Cu: 805; whence we deduce the formula, 3Cu P+10 H, requiring an oxygen ratio of 13 13 8.66.

4. Phosphate of Copper, from Hirschberg.

According to Kühn, its constituents are, phosphoric acid 20-87, oxyd of copper 71-73, water 7-40 100.00; whence we obtain the oxygen ratio,

11-69 P 17-66 (R) Į
11.69 : 17.54

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IV. ARSENIATES.

(Cu) 1 5 P2.

As the relative quantities of the peroxyd and the protoxyd of iron have not yet been ascertained with accuracy in scorodite and in pharmacolite, no calculations can be here entered upon with respect to the formula these minerals would receive, by considering their water as a basic constituent.

A. Arseniates of Earths.

Picropharmacolite.

The analysis of Stromeyer gives arsenic acid 46.971, lime 24-646, magnesia 3·223, oxyd of cobalt 0.998, water 23-977 = 99.815, corresponding to

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the formula of vivianite, libethenite, and earthy blue iron. Since pharmacolite contains no earth but lime, it is not to be assumed that any replacement by water is brought into play in that mineral.

B. Arseniates of Cobalt.

Cobalt Bloom.

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According to Berzelius, its formula is Co3 As+6H, which, as protoxyd of iron and protoxyd of cobalt are isomorphous, and as we may make 3H 1Co, may be expressed likewise thus, (Co) As, by which it is rendered analogous to the Cornish vivianite; and the agreement that has been proved by Gustavus Rose

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to exist between the forms of the crystals of these two minerals, would be thus farther borne out. According to Kersten's analysis of the cobalt bloom from Schneeberg, the formula for this mineral is however, Co3 As +8H.

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This too is the formula of vivianite and of the other minerals

cited. It is assumed that 2 = 1Cu.

2. Euchroite.

The euchroite from Libethen consists, according to Turner, of arsenic acid 32.02, oxyd of copper 47-85, water 8.80 = 99.67. From this the following oxygen ratio may be deduced, 11:47 As : 12·00 (Ċu): 12·01H, approaching very closely the ratio calculated for phosphorochalcite, and whence may be deduced the formula, (Cu) As+5H. In euchroite however, a larger portion of the water (about one-fourth of the whole amount) plays the part of a base, than is the case in phosphorochalcite.

3. Copper-foam.

According to v. Kobell's analysis, the formula of the diverging foliated copper-foam from Falkenstein, is Cu As+10H, not taking into account the quantity of carbonate of lime therein contained, the amount of which approaches 1 atom.

4. Erinite.

From Turner's approximative analysis of this mineral, its constituents are arsenic acid 33 78, oxyd of copper 59-44, water 5:01, alumina 1·77 = 100.00. Neglecting the alumina, this gives the following oxygen ratio, 11-73 As: 11.99 Cu: 4.45 H, whence may be deduced the formula, 2Cu As+5H, or perhaps rather, 3Cu As+5. The former requires an oxygen ratio of 11: 11: 5.5,—the latter of 12 12 4.

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