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 C40 H31 N5 012. 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, To Professor JAMESON, Edinburgh. JAMES F. W. JOHNSTON. 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 you change these names, then everything else remains the same. What I formerly distinguished by the name of sulpho-proteic acid, ought 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 combinations 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. They― the 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 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 H25 N 010 + 2 HO. 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 you have formerly stated regarding nothing is modified but the formula. sessed, viz: that every thing is modified that protein? On the contrary, Science retains what it pos 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 Rüling,† (C=75 12; N=87.5), and the new determinations of sulphur consists of This composition represents a combination of 20 equiv. of protein + HO, 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.§ chlorite of casein, and, III.,|| chlorite of fibrin, *Scheik. Onderz. deel iii. † Ann. der Chem. und Pharm., 1846, || Ibid. § Ibid. I have, for simplicity, left out the phosphorus; I do not even know if it exists in this compound. The quantity of sulphamid in fibrin and casein is different from that in albumen, but the difference is small, and therefore I pass it over here. These bodies are the chlorites of albumen, fibrin, and casein. They produce sulphuret of silver, on being heated with potash upon silver, and thus they can be easily distinguished from the chlorite of protein containing hyposulphurous acid, which does not possess this property. The latter may be prepared in different ways-among others, from the solutions, from which protein has been precipitated, or by passing chlorine, for a long time, through a mixture of albumen, fibrin, casein, horn, hair, whalebone, &c., and water. The product always contains a certain quantity of hyposulphurous acid arising from the decomposition of sulphamid and water 2 (S N H2 + H 0). The action of the chlorine upon this produces ammonia, which unites with hydrochloric acid, and hyposulphurous acid, which, along with chlorous acid, is taken up by the organic compound. In my former letter to you, I reduced the composition of protein with hyposulphurous acid, as it is obtained from albumen, to a group free from this mixture. I then brought into account 1.4 per cent. of sulphur, as was found by Fleitmann. The normal quantity obtained by fusion with soda, and subsequent addition of saltpetre, is 1.6 per cent., and this I believe to be the true proportion of sulphur in albumen. The compound consists of |
