1118. "The two ureas, however, are far from being identical. The urea obtained by combining cyanate of ethyl with ethylene-diamine is easily soluble in boiling water, difficultly soluble in cold water, even less soluble in spirit, and almost insoluble in absolute alcohol. It fuses without decomposition at 2010, solidifying again at 185°. This body is altogether indifferent. I did not succeed in obtaining a platinum salt or a gold salt of this urea, while the isomeric substance derived from ethylenediethylamine furnishes both salts without difficulty.

1119. "The non-identity of the two bodies is thus sufficiently established, but the absolute difference in their construction is most conspicuously manifested in the products of decomposition which they yield under the influence of the alkalies. Treated with potash, the urea derived from ethylene-diethyl-diamine and cyanic acid, yields ethylene-diethyl-diamine and the products of decomposition of cyanic acid,-carbonic acid and ammonia. The urea, on the other hand, which is formed by the action of ethylene-diamine on cyanic ether, splits into ethylene-diamine, and the derivatives of cyanic ether, carbonic acid, and ethylamine.

1120. "It is thus evident that the two individual groups of elements, the union of which gives rise to the two different ethylated ethylene-ureas, remain as such, unaltered in these compounds."*

APPENDIX L.

1121. We must here inform the student that a great many important organic bodies, as the sugars, starches, gums, essential oils not containing oxygen, have not been noticed at all in any one of the last four chapters, although in these chapters organic bodies have been treated of to a considerable extent. The reason why they were omitted is this, we cannot as yet refer them to any type. It is possible that the sugars may prove, like manníte, to be alcohols, but at present we have either no evidence, or not sufficient evidence, to refer these, or any of the other important bodies I have named, to any type.

Dr. Volhard "On the Ureas of the Diamines." "Proceedings of the Royal Society," vol. xi., No. 44.

1122. I have placed at the end of the book a series of questions on chemistry and chemical physics, which I have selected from the published examination papers of different examiners. I recommend the student to write out answers to the questions grouped under the head of chemistry, before he passes on to the next chapter.

CHAPTER XI.

OTHER VIEWS ON THE CONSTITUTION OF BODIES.

Wurtz's views, 1127. Dr. Lyon Playfair's views, 1136. Dr. Frankland's views, 1140. Dr. Kolbe's views, 1170. Appendix M.

1123. The student has already been made aware (pars. 529 to 533, and Appendix B, page 279) that, since the time Gerhardt and his followers first propounded the theory "that the molecules of all bodies occupy two volumes in the vapourous state," a number of facts have been discovered, which renders it imperative on chemists either to abandon that theory, or, if they continue to adopt it, to alter the atomic weights of a large number of the elements. Thus, in two gaseous volumes of the hydrides of the alcohol radicals, there are contained one atom of hydrogen and one of the compound radical. Now, as the metals have hitherto been considered the strict representatives of hydrogen, we should expect to find that in two volumes of the vapour of organo-metallic bodies there would be, as in the case of the hydrides, an equivalent of metal, and an equivalent of the alcohol radical; but this is not the case; in the two volumes of these bodies there are two equivalents of metal and two of the alcohol radicals. Nor is this difference between the condensation of hydrogen and the metals confined to organic compounds; it has been ascertained, from taking the vapour densities of various metallic chlorides, that the metals in various chlorides are in a more condensed form than the hydrogen in hydrochloric acid; therefore, if we admit that the molecules of all substances occupy two volumes in the

gaseous state, and if the reasoning which has led chemists to double the atomic weight of oxygen be correct, the same reasoning must lead us to double the atomic weights of the greater number of the elements.

1124. These reasons have been very ably set forth by Dr. Wolcott Gibbs, in a paper which appeared in the American Journal of Science: this paper I have given almost in its entirety. That part of it which relates to the doubling of the atomic weights of other elements besides carbon, oxygen, and sulphur, is given in Appendix B, page 279. Since that part of my work was in print, a paper by Wurtz on the same subject has appeared in the Journal of the Chemical Society of London; * the title of the paper is "On Oxide of Ethylene, considered as a link between Organic and Mineral Chemistry." The object of the paper is to prove that the present atomic weights of Ba, Sr, Ca, Mg, Mn, Fe, Zn, Cd, Cu, Pb, Hg, Sn, &c., ought to be doubled. He first proves that the new atomic weights accord better than any other with the atomic heats of the elements, with the laws of isomorphism, with the vapour densities of a great number of bodies; these physical proofs, with the exception of isomorphism, have been given in Gibbs' paper. He then adduces purely chemical proofs: he shows that the oxides of the metals, the atomic weights of which he proposes to double, and if they are doubled, the metals become diatomic,-resemble in their chemical properties the oxide of the diatomic radical ethylene, he shows that they resemble oxide of ethylene in the formation of their hydrates, in the formation of their neutral and basic salts, in the formation of oxychlorides, oxy fluorides, in the formation of diammonium compounds, &c.; whereas, oxide of silver, and the oxides of the other metals which are considered monatomic, do not resemble oxide of ethy lene, but resemble the oxides of the monatomic alcohol radicals in their chemical properties; therefore, as the oxides of Ba, Pb, Cu, &c., resemble in their chemical deportment the oxide of the diatomic radical ethylene, those metals must be diatomic, and, consequently, their atomic weights must be doubled.

1125. As Dr. Wolcott Gibbs did not adduce any reasons

* Vol. xv., p. 387.

derived from the chemical deportment of the bodies for doubling their atomic weights, I have thought it necessary to place in a condensed form the paper of Wurtz before the student, as the question of atomic weights and the constitution of bodies is a most important one.

1126. Dr. Lyon Playfair, Dr. Frankland, and Dr. Kolbe, have each proposed views on the constitution of bodies which differ from those adopted by Gerhardt and his followers: these views are brought before the student in the present chapter.

1127. The views of Wurtz.-Oxide of ethylene can displace magnesia, alumina, ferric oxide, and cupric oxide, from their acid combinations; it has, therefore, strong basic properties.

1128. Now, as the radical in oxide of ethylene is diatomic, the question arises, Are there any metallic oxides, the metals in which are diatomic? He considers that the atomic weights of Ba, Sr, Ca, Mg, Mn, Fe (ferrosum), Zn, Cu, Pb, Hg, &c., are double those which are commonly assigned to them, and therefore they become diatomic; consequently their oxides correspond, or are comparable with oxide of ethylene. The arguments which Wurtz adduces in support of the view that these metals have double the atomic weight usually assigned them, we will presently lay before the student; but we will first contrast the atomic weights of Berzelius, Gerhardt, and those proposed by Wurtz, for a few of the elements :

1129. For a considerable number of the metals, the new atomic weights and those of Berzelius correspond, being double those proposed by Gerhardt; therefore, the new formulæ for the oxides, &c., of these metals are identical with the old formulæ of Berzelius:* he wrote Ba O; Ba S; Ba O, H, O; Ba Cl2; Ba SO, &c. We return to these formulæ, but we agree with Gerhardt in writing K, O; K2S; KHO; K CI; K, SO, &c.

1130. The new atomic weights correspond with those of Gerhardt for the metals Ag; K; Na; Li: these metals are monatomic, and, therefore, comparable with hydrogen.

1131. The new system of atomic weights accords better than any other with the physical data which serve to control the determination of the relative weights of the atoms. In fact, the numbers in the last column are identical with those designated by M. Regnault as "thermic equivalents." Thermic equivalents are fully considered in Chapter XIII; on that account we shall not now enter more fully upon the subject.

1132. In the next place, the new system of atomic weights is in harmony with the law of isomorphism, which requires that isomorphous bodies be represented by analogous formulæ. Thus, cuprous sulphide is isomorphous with sulphide of silver (see par. 265), and these two bodies have in the new system analogous formulæ, viz., Ag, S and Cu, S; whereas, by the formulæ assigned to them by Gerhardt, they had not an analogous composi

* See par. 277.