in the way have not obtained results of a very conclusive kind. It is known that the product when strongly heated in a current of ammonia gas affords ammonium chloride, which volatilises, and a residue, to which Schutzenberger and Colson have assigned the formula Si,N,H. This body they regard as a definite hydride of Si,N, which latter they produced by acting on silicon at a white heat with pure nitrogen. Gattermann suggests that a nearer approach to the silicon analogue of cyanogen, Si,N,, should be obtained from the product of the action of ammonia on silicon-chloroform; but it does not appear that this suggestion has yet borne fruit. It was scarcely probable that the above-mentioned rather indefinite compounds of silicon with nitrogen were the only ones of the class obtainable, since bodies including carbon combined with nitrogen are not only numerous but are among the most important carbon compounds known. Further investigation was therefore necessary in the interests of comparative chemistry, and for special reasons which will appear later on; but it was evident that a new point of attack must be found. A preliminary experimental survey proved the possibility of forming numerous compounds of silicon containing nitrogen, and enabled me to select those which seemed most likely to afford definite information. For much of this kind of work silicon chloride was rather too energetic, hence I had a considerable quantity of the more manageable silicon tetrabromide prepared by Serullas' method, viz., by passing the vapour of crude bromine (containing a little chlorine) over a strongly heated mixture of silica and charcoal. In purifying this product I obtained incidentally the chloro-bromide of silicon, SiCIBr,, which was required in order to complete the series of possible chlorobromides of silicon.1 Silicon bromide was found to produce addition compounds very readily with many feebly basic substances containing nitrogen. But one group of bromides of this class has yet been investigated in detail, namely, the products afforded by thioureas. The typical member of this group is the perfectly definite but uncrystalline substance Substituted thioureas afford similar bodies, the most interesting of which is the allyl compound. This is a singularly viscid liquid, which requires several days at ordinary temperatures to regain its level, when a tube containing it is inverted. But these are essentially addition compounds, and are therefore comparatively unimportant. In most cases, however, the silicon haloids enter into very definite reaction with nitrogen compounds, especially when the latter are distinctly basic, such as aniline or any of its homologues. One of the principal products of this class of change is the beautiful typical substance on the table, which is the first well-defined crystalline compound obtained in which silicon is exclusively combined with nitrogen. Its composition is Si(NHC,H,),." Analogous compounds have been formed with the toluidines, naphthylamines, &c., and have been examined in considerable detail, but it suffices to mention them and proceed to point out the nature of the changes we can effect by the action of heat on the comparatively simple anilide. When silicon anilide is heated carefully in vacuo it loses one molecule of aniline very easily and leaves triphenyl-guanidine, probably the a modification; if the action of heat be continued, but at ordinary pressure and in a current of dry hydrogen, another molecule of aniline can be expelled, and, just before the last trace of the latter is removed, the previously liquid substance solidifies and affords a silicon analogue of the insoluble modification of carbodiphenyldiimide, which may then be heated moderately without undergoing further material change. A comparison of the formule will make the relations of the products clear : Silicotetraphenylamide-Si (NHPh), 'Three years later Besson formed the same compound and described it as new. 2 Harden has obtained an uncrystalline intermediate compound, SiCl,(NHC.H1) Moreover, the diimide has been heated to full redness in a gas combustion furnace while dry hydrogen was still passed over it; even under these conditions little charring occurred, but some nitrogen and a phenyl radical were eliminated, and the purified residue was found to approximate in composition to SiNPh, which would represent the body as phenylsilicocyanide or a polymer of it. Even careful heating of the diimide in ammonia gas has not enabled me to remove all the phenyl from the compound, but rather to retain nitrogen, as the best residue obtained from such treatment consisted of Si,N,Ph, or the phenylic derivative of one of the substances produced by Schutzenberger and Colson from the ammonia reaction. It may be that both these substances are compounds of silicocyanogen with an imide group of the kind indicated below Further investigation must decide whether this is a real relationship; if it be, we should be able to remove the imidic group and obtain silicocyanogen in the free state. One other point only need be noticed, namely, that when the above silicon compounds are heated in oxygen they are slowly converted into SiO,; but the last traces of nitrogen are removed with great difficulty, unless water-vapour is present, when ammonia and silica are quickly formed. Much remains to be done in this department of comparative chemistry, but we may fairly claim to have established the fact that silicon, like carbon, can be made to form perfectly well-defined compounds in which it is exclusively united with the triad nitrogen of amidic and imidic groups. Now, having proved the capacity of silicon for the formation of compounds of this order with a triad element, Nature very distinctively lets us understand that nitrogen is not the particular element which is best adapted to play the triad rôle towards silicon in its high-temperature changes, which are ultimately dominated by oxygen. We are not acquainted with any natural compounds which include silicon and nitrogen; but large numbers of the most important minerals contain the pseudo-triad element aluminium combined with silicon, and few include any other triad. Phosphorus follows silicon in the periodic system of the elements as nitrogen does carbon, but silicates containing more than traces of phosphorus are rare; on the other hand, several silicates are known containing boron, the lower homologue of aluminium; for example, axinite, datholite, and tourmaline. Moreover, it is well known that silicon dissolves freely in molten aluminium, though much of the former separates on cooling. Winkler has analysed the gangue of aluminium saturated with silicon, and found that its composition is approximately represented by the formula SiAl, or, perhaps, Si,Al, if we are to regard this as analogous to C,N, or cyanogen. Here aluminium at least resembles nitrogen in directly forming a compound with silicon at moderately high temperature. It would appear, then, that while silicon can combine with both the triads nitrogen and aluminium, the marked positive characters of the latter, and its extremely low volatility, suit it best for the production of permanent silicon compounds similar to those which nitrogen can afford. With these facts in mind we may carry our thoughts back to that period in the earth's history when our planet was at a higher temperature than the dissociation point of oxygen compounds. Under such conditions the least volatile elements were probably liquids, while silicides and carbides of various metals were formed in the fluid globe. We can imagine that the attraction of aluminium for the large excess of silicon would assert itself, and that, as the temperature fell below the point at which oxidation became possible, these silicides and carbides underwent some degree of oxidation, the carbides suffering most owing to the volatility of the oxides of carbon, while the fixity of the products of oxidation of silicides rendered the latter process a more gradual one. The oxidation of silicides of metals which had little attraction for silicon would lead to the formation of simple metallic silicates and to the separation of the large quantities of free silica we meet with in the solid crust of the earth, whereas oxidation of silicides of aluminium would not break up the union of the two elements, but rather cause the ultimate formation of the alumino-silicates which are so abundant in most of our rocks. Viewed in the light of the facts already cited and the inferences we have drawn from them as to the nitrogen-like relationship of aluminium to silicon, I am disposed to regard the natural alumino-silicates as products of final oxidation of sometime active silico-aluminium analogues of carbo-nitrogen compounds, rather than ordinary double salts. It is generally taken for granted that they are double salts, but recent work on the chromoxalates by E. A. Werner has shown that this view is not necessarily true of all such substances. Without going into undue detail we can even form some conception of the general course of change from simple aluminium silicide to an alumino-silicate, if we allow the analogies already traced to lead us further. We recognise the existence of silico-formyl in Friedel and Ladenburg's silicoformic anhydride; hence silico-triformamide is a compound whose probable formation we can admit, and, on the basis of our aluminium-nitrogen analogy, an aluminium representative also. Thus Now, oxidation of triformamide would lead to complete resolution into nitrogen gas, carbondioxide gas and water rendering it an extremely unstable body; under similar conditions silico-triformamide would probably afford nitrogen gas and silicic acid (or silicon dioxide and water); while the third compound, instead of breaking up, would (owing to the fixity of aluminium as compared with nitrogen) be likely at first to afford a salt of an alumino-silicic acid, in presence of much basic material. The frequent recurrence of the ratios Si,Al, Si,Al2, &c., in the formulæ of natural alumino-silicates, suggests that some at least of these minerals are derived from oxidation products of the above triformic type. Without stopping to trace all the possible stages in the oxidation of the primary compound Al(SiO2R), or variations in basicity of the products, I may cite the four following examples out of many others which might be given of resulting representative mineral groups :SiO,R'3 SiO,R' \SiO,R' Beryl type (hemi-). SiO,R', Al-SiO,R's \Sio,R"" : Garnet type. SiO,R" 1 Al-SiO,R""' \Sio,R""' Xenolite type. Five years ago Professor F. W. Clarke, of the United States Geological Survey, published a most interesting paper on the structure of the natural silicates. In this he adopts the view that the mineral xenolite, Si,A1012, is the primary from which all other alumino-silicates may be supposed to arise by various substitutions. Nature, however, seems to teach us that such minerals as xenolite, fibrolite, and the related group of clays' are rather to be regarded as end-products of a series of hydrolytic changes of less aluminous silicates than primary substances themselves; hence the sketch which I have ventured to give above of the probable genesis of alumino-silicates seems to provide a less arbitrary basis for Clarke's interesting work, without materially disturbing the general drift of his subsequent reasoning. We may now consider for a moment in what direction evidence can be sought for the existence in nature of derivatives of the hypothetical intermediate products of oxidation between a primary silicide and its fully oxidised silicate. = In these cases where R"" Al it is, of course, assumed that the latter is acting only as a basic radical. In the absence of a working hypothesis of the kind which I have already suggested, it is not probable that direct evidence would yet be obtainable-this must be work for the future-but when we consider that the existence of compounds of the order in question would manifest themselves in ordinary mineral analyses by the analytical products exceeding the original weight of material, we seem to find some evidence on the point in recorded cases of the kind. A deficiency of a single atom of oxygen in compounds having the high molecular weights of those in question would be indicated by very small excesses (from 2 to 3 per cent.) whose real meaning might be easily overlooked. Now, such results are not at all unusual in analyses of mineral alumino-silicates. For instance, Amphiboles containing a mere trace of iron have afforded 102.75 parts from 100, and almost all analyses of Microsommite are high, giving as much as 103 parts. In less degree Vesuvianite and members of the Andalusite group may be noted. All these cases may be capable of some other explanations, but I cite them to show that such excesses are commonly met with in published analyses. On the other hand, it is scarcely to be doubted that a good analyst, who obtained a really significant excess, would throw such a result aside as erroneous and never publish it. I therefore plead for much greater care in analyses of the kind in question and closer scrutiny of results in the light of the suggestions I have ventured to offer. It is probable that silicates containing only partially oxidised aluminium are rare; nevertheless the search for them would introduce a new element of interest into mineralogical inquiries. If the general considerations I have now endeavoured to lay before you are allowed their full weight, some of the alumino-silicates of our primary rocks reveal to us more than we hitherto supposed. Regarded from this newer standpoint, they are teleoxidised representatives of substances which foreshadowed in terms of silicon, aluminium, and oxygen the compounds of carbon, nitrogen, and hydrogen required at a later stage of the earth's history for living organisms. Thus, while the sedimentary strata contain remains which come down to us from the very dawn of life on this globe, the rocks from whose partial disintegration the preserving strata resulted contain mineral records which carry us still further back, even to Nature's earliest efforts in building up compounds similar to those suited for the purposes of organic development. The following Papers and Reports were read:- 1. On Tools and Ornaments of Copper and Other Metals from Egypt and Palestine. By Dr. J. H. GLADSTONE, F.R.S. The author gave an account of analyses of various specimens of metallic tools and ornaments found by Dr. Flinders Petrie in Egypt and Mr. Bliss in Palestine. The oldest copper tools were from Meydum, and date back probably to the fourth Egyptian dynasty, about 3500 B.C. Other copper tools were obtained at Kahun, and date 2500 B.C. These contain small quantities of arsenic, antimony, &c.; but among the specimens from Meydum was a rod of bronze containing about 9 per cent. of tin. Bronze needles were also found at Kahun, and of course bronze was abundant in later periods. That tin was known in the metallic condition was evidenced by a finger-ring made of tin belonging to the eighteenth dynasty, about 1400 B.C. Lead was often mixed with the bronze for the casting of statuettes. The mound of Tel-el-Hesy, which is believed to be the Lachish of the Scriptures, consists of the ruins of several successive Amorite towns, above which are the ruins of the Israelitish town. A copper tool from the lowest stratum, and which could not be of later date than 1500 B.C., was made of a very red, hard, brittle metal, of a specific gravity of only 6-6, and consisted of cuprous oxide to the extent of about 25 per cent. This oxide, no doubt, gave the desired hardness to the copper. In the strata dating from 1400 B.c. to 800 B.C. occurred many arrow-heads and other objects made of bronze. In the upper Israelitish portion the bronze implements were gradually replaced by iron. At Lachish there were also found a wire of almost pure lead, and what seemed to be a bracelet of silver. The latter was coated with chloride of silver, doubtless from the chlorides in the soil, and contained 6.5 per cent. of copper and 1.44 per cent. of gold. At Illahun, in Egypt, some beads or buttons were found which proved to be of metallic antimony badly reduced from the sulphide. They date back to about 800 B.C. 2. Report on International Standards for the Analysis of Iron and Steel. See Reports, p. 437. 3. On Native Iron Manufacture in Bengal. By H. HARRIS and T. Turner. 4. On Nitride of Iron. By G. J. FOWLER, M.Sc. This research was undertaken with the object of repeating and extending the work of Stahlschmidt ('Pogg. Ann.,' v. cxxv., 1865, p. 37) on the same subject, his results differing in many points from those of his predecessors. The best way of preparing nitride of iron was found to be the following:-Iron is reduced from the hydrate by hydrogen, in a tube of such dimensions that it can be weighed, together with its contents, and thus the end of the reaction determined without exposing the iron to the air. When complete reduction has been effected, the iron is heated in a fairly rapid current of ammonia gas, until no further increase in weight is observed. The temperature should be kept a little above the melting-point of lead. The product obtained when the reaction was complete was analysed. The nitrogen was determined by dissolving the substance in hydrochloric acid, evaporating with platinum chloride, and weighing the ammonium-platinum-chloride obtained. The hydrogen given off on solution of the substance in sulphuric acid was measured. The iron was determined by ignition and weighing as oxide, and by solution in sulphuric acid and titration with permanganate. As will be seen from the results obtained, the nitride prepared as above has a composition corresponding to the formula Fe,N. On solution in hydrochloric acid the following reaction takes place :— In another sample 10.94 N. was found. In a third case, in which the iron, after solution of the nitride in acid, was precipitated by ammonia and weighed as oxide, 89.44 per cent. of iron was obtained and 10.5 per cent. of nitrogen, showing again that the substance dissolves in acid according to the above equation, all the nitrogen being converted into ammonia. No percentages of nitrogen above 11.1 could be obtained, while any percentage below that could be got according to the time during which the iron had been exposed to the current of ammonia. These results are fully in agreement with those obtained by Stahlschmidt, and confirm his conclusion that only one nitride of iron exists, and that it has the above composition. Nitride of iron is formed when iron amalgam is heated in ammonia, and also when ferrous chloride or bromide is heated in this gas. These methods, however, do not so readily give a product containing the full percentage of nitrogen, and free from the presence of a third element. Nitride of iron is a grey powder, rather less blue in tone than iron reduced from |