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are indeed authors who think, that the Upper Silurian is so linked on to the Devonian, that the former, or a large portion of it, might advantageously be merged in the latter ; and if their views prevailed, the only portion of my system or terrain which Professor Sedgwick's proposition leaves to me would also be swallowed up, and thus, by invasions on both sides, the poor Silurian system would be obliterated.

On the principle, however, of strata identified by their fossils, geologists, I hope, agree with me to the conviction in which I abide, that in whatever rocks, and to whatever depths the Lower Silurian types extend, the tracts so characterised must be considered to belong to the “ Silurian System.”

In contending for the preservation of that system in its unity, I in no way detract from the very great merit of the researches of my friend, Professor Sedgwick, in developing the physical structure, dislocations, slaty impress, fossil characters, and other phenomena of the rocks of North Wales, Cumberland, and Westmoreland.

As already stated, I formerly hoped he would also point out in their lowest division the existence of a distinct zoological type which would have entitled those rocks to a separate name; but having failed to do so, it seems to me manifest, that his "Cambrian” cannot now be sustained by dismembering a fossiliferous system which has been so long established, so largely developed, and so widely applied over the world as the Silurian. Whether geologists will use the word • Cambrian,” in reference to still older and often unconformable greywacke lying beneath all the beds with Silurian fossils, it is not for me to determine. My chief object in this communication is to explain how, by the progress of research, the protozoic types of various parts of Northern Europe, including North Wales, have been shewn to be true equivalents of the lower part of a natural system which I proposed twelve years ago, and which geologists of various countries adopted after a careful scrutiny of the evidences on which it was established.

On the Protein Question. By Professor MULDER of Utrecht.

Communicated by Professor J. F. W. JOHNSTON.

DURHAM, 17th June 1847. MY DEAR SIR,-Will you favour me by inserting in your ensuing number, the following additional communication from Professor Mulder on the Protein question? The perusal of it will shew you that we are slowly progressing towards a more perfect knowledge of this important substance.

The state of our knowledge in regard to it is at present nearly as follows:

1. There exists in the parts of animals and plants a substance to

which the name of protein is given, and which, according to the analyses hitherto made, may be most nearly represented by the empirical formula,

C36 H25 N° 010 + 2 HO.

The older formula, now abandoned by Mulder, was

C'ł0 H31 N5 012. C

The latter of these formulæ contains a larger proportion of nitrogen than the one now adopted. This arises from the circumstance that a part of the nitrogen supposed formerly to belong to the protein is now found to exist in it in a different state (that of an amid), and not properly to belong to the composition of the pure protein itself.

2. That this protein combines with the amid of the hypo-sulphorous, and probably of the hypo-phosphorous acid, and forms combinations which occur abundantly in nature. Albumen, casein, fibrin, &c., are such natural combinations. The nitrogen of these amids was included in the old formula for protein, and hence, when it is abstracted, the new formula must contain less nitrogen.

3. That these combinations of protein with the amids, when heated upon a plate of silver, with a few drops of a solution of caustic potash, evolve ammonia and sulphuretted hydrogen ; which last product blackens the surface of the polished silver.

4. That they also unite directly with the chlorous, the tannic, and other acids, forming combinations of the natural albumen, casein, &c., with these acids. Such a compound with albumen is formed when a solution of tannic acid is poured into an aqueous solution of the white of egg. These compounds all blacken silver under the influence of caustic potash, as the albumen and casein themselves do.

5. That by the prolonged action of caustic potash, aided by a gentle heat and access of air, the amids contained in these natural compounds are decomposed—their nitrogen more or less completely separated in the form of ammonia, and their sulphur converted into sulphurous and phosphorous acids which combine directly with the protein. When separated from the potash by acetic acid, the combination obtained contains these two acids in variable proportions, and does not blacken silver when treated as above described.

The prolonged action of chlorine produces a similar effect-forming at first compounds of the chlorous sulphurous and phosphorous acids with protein, which do not blacken silver.

6. But that by a prolonged action of chlorine under other known circumstances, the proportion of the sulphurous and phosphorous acids in these compounds diminishes, and becomes very variable. Mixtures in fact are obtained in which pure chlorite of protein exists contaminated with more or less of certain compounds of the same chlorite with the acids of sulphur and phosphorus.

Thus far at present-irrespective of personal contentions—our groping after the truth seems to carry us.—Believe me, yours very truly,

JAMES F. W. JOHNSTON. To Professor JAMESON, Edinburgh.

UTRECHT, 27th May 1847. MY DEAR FRIEND,—The albuminous bodies about which I wrote you some time ago, required a detailed investigation, in consequence of what I had discovered, namely, that the sulphur and phosphorus they contain, exists in the state of sulphamid and phosphamid, and that hyposulphurous acid is present in the precipitate produced by dissolving them in caustic potash, by the aid of heat, and adding acetic acid in excess.

I have, without intermission, continued my investigations, and the result is, that the above named constitution is common to them all. Hair, whalebone, casein, legumin, albumen, fibrin, horny matter and the nails, consist of nothing else than the above amids, combined in different proportions, either with protein, or with an organic group, which can bear no other name than that of oxide of protein. I formerly gave you instances of this in the composition of fibrin, horn, and legumin.

It is evident, after this discovery, that the empirical formula, by which we have hitherto represented protein, ought to receive some modification. All my former results tend to corroborate this, and you

will find, that all that is necessary is a change of names, and that the results of my former analyses remain unaffected. It was wrong, therefore, to attempt to throw suspicion upon my results. Only, what I formerly called chlorite of protein, must receive the name of chlorite of albumen, of casein, and of fibrin, and if change these names, then everything else remains the same. What I formerly distinguished by the name of sulpho-proteic acid, fought to be called sulphate of albumen, or of casein, but the analytical results stand unaltered.

It is only by my present investigations that I have become acquainted with chlorite and sulphate of protein. In composition and properties, they very much resemble the con binations of Chlorous and sulphuric acid, with albumen, casein, &c.; but when heated with potash upon a silver plate, they do not produce a black spot. Theythe chlorites, that is to say—all contain a small quantity of hyposulphurous acid; but, in some compounds, which otherwise are pure chlorites of protein, this hyposulphurous acid does not amount to more than 0-6 per cent. They thus prove, that this hyposulphurous acid, of which very variable quantities may also exist in protein, is not an essential ingredient of it; and, further, that notwithstanding all the trouble that is taken now to direct attention to this sulphur, it will be an unsuccessful attempt to deny the existence of an inde

you

pendent organic group, which is free from sulphur in every sense of the word.

If, for instance, a current of chlorine is passed through a solution of albumen, for several days together, we obtain not a product of decomposition, but a real combination of chlorous acid with protein, which does not blacken silver. The quantity of sulphur it contains, in the form of hyposulphurous acid, is equal to that of the sulphamid of an equivalent quantity of albumen. According to Kemp, this would amount to 1.5 per cent. in the chlorite compound; but this is too high, as I shall prove below. If duly prepared, it does not contain more than 1.2 of sulphur, equal to 1.83 per cent. of hyposulphurous acid.

But this proportion is far from being constant or essential; for if a current of chlorine is passed through the acetic acid solution, from which protein from fibrin has been precipitated, we obtain a chlorite of protein, perfectly similar to that from albumen, but containing only 0.4 per cent. of sulphur =0.6 per cent. of hyposulphurous acid.

Similar discrepancies are found in the quantity of hyposulphurous acid, existing in protein itself.

After this sulphur question has produced its effect, it will descend into the place which it ought to occupy.

The maximum quantity of hyposulphurous acid which I have been able hitherto to find in, or to be taken up by protein, is 2:4 per cent., equal to 1.6 per cent. of sulphur—that is the quantity which is found in albumen, under the form of sulphamid. It represents exactly the half, in equivalents, of the quantity of hydrochloric acid, that can be taken up by albumen. This combination, therefore, cannot be called strange or singular. The hyposulphurous acid obstinately adheres to the protein in the same manner as sulphuric acid, phosphate of lime, metallic oxides, and several other bodies, all of which may unite with it in small quantities.

The composition of protein, free from sulphur in every form, may be represented by the following empirical formula :

C36 H 25 N 010 + 2 H 0. It differs from the one to which I have hitherto adhered, because the organic group contains a little less nitrogen than was ascribed to it before. This is all the modification which my former results require. The formula expresses in 100 parts:

C 54.7
H 6.8
N 14.2
O 24.3

The grounds upon which I propose this formula, are not more

certain than those for all empirical formulæ. We have seen this in the case of salicine. All the empirical formulæ, which equally expressed the composition of salicine, fell to the ground after Piria had discovered its constitution. Yet the formula above given brings us a little nearer to the truth.

Perhaps it may be said, —And so every thing is modified that you have formerly stated regarding protein ? On the contrary, nothing is modified but the formula. Science retains what it possessed, viz: that

1st, The vegetable and animal albuminous bodies contain in common an organic group free from sulphur,

2d, There are two groups to be considered as higher degrees of oxidation of the former, and produced from protein.

I will give you the new form, into which my previous results require to be moulded. It will thence be evident to you, that with the exception of the nitrogen of the protein itself, nothing at all of my former results is altered.

Albumen from eggs, according to my former analyses, * and those of Ruling,t (C=75:12; N=87.5), and the new determinations of sulphur consists of

[blocks in formation]

This composition represents a combinaticn of 20 equiv. of protein + H 0, with 8 equiv. of sulphamid and 1 equiv. of phosphamid. Kemp designates this explanation by the name of an artifice. This expression, however, is not accurate. It is nothing else than an attempt on my part, to give a certain form to what I have found. If the quantity of phosphamid in the combustion were double, it would be reduced to the simple form of 2 equiv. of protein + 1 equiv. of amid of sulphur and phosphorus.

Now, by the influence of chlorine, this albumen combines, without undergoing a change, with chlorous acid, and the product is chlorite of albumen, I. which I before wrongly called chlorite of protein; I add, II.S chlorite of casein, and, III., chlorite of fibrin,

* Scheik. Onderz. deel iii.
# Bulletin, 1839, p. 400.

† Ann. der Chem, und Pharm., 1846. $ Ibid.

11 Ibid.

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