Nov. 5, 1 885] 



NA TURE 



not out of accord witli Sir W. Thomson's estimate of the size of 

 molecules. 



On Macro-molecules, with the Determinations oj the Form of 

 some of them, by Prof. G. Johnstone Stoney, D.Sc, F.R.S. — 

 The author suggested that the molecule of a crystal, which in 

 all probability, consists of several chemical molecules, should be 

 termed a macro-molecule. He then went on to show that it is 

 possible to deduce the form of the macro-molecule from the 

 composition of the chemical molecule ; this he illustrated by the 

 cases of iron pyrites, boracite, and quartz. 



An Approximate- Detertnination of the Absolute Amount of 

 the lVeif;kt of Chemical Atotns, by Prof. G. Johnstone Stoney, 

 D.Sc, F.R.S. — The author showed that the mass of a molecule 

 of hydrogen is a quantity of the same order as a decigramme 

 divided by lo-'' — i.e. a twenty-fourth decigrammet, which is the 

 same as the twenty-fifth grammet. (The grammets are the 

 decimal sub-divisions of the gramme, of which the first is the 

 decigramme, the second the centigramme, &c.) The mass of 

 the chemical atom of hydrogen may be taken to be half the 

 twenty-fifth of the grammet. This value is based on the con- 

 clusion arrived at by several physicists — that the number of 



! molecules in a cubic millimetre of a gas at ordinary tem]jerature 

 and pressure is somewhere about a unit eighteen {10''^), from 

 which it can be shown that the number of molecules per litre 

 must be about a unit twenty-four (lO'-^j. From this, together 

 with a knowledge of the weight of a litre of hydrogen, the above 

 value for the mass of a molecule of hydrogen has been deduced. The 

 mass of a molecule of hydrogen being known, it is possible now 



] to determine approximately the masses of all other simple sub- 

 stances and of compounds also. 



Prof. Osborne Reynolds then made a communication to the 

 Section on the subject of Dilatancy, which was also read before 

 Section A (see Nature, vol. .\.Kxii. p. 535). 



On Physical Molecular Equivalents, by Prof. F. Guthrie, 

 F.R.S. — The author pointed out that the cryohydrates are solid 

 compounds of water and salts possessing very low melting-points, 



I in which the mass ratios, whilst definite, are other than those of 

 the ordinary chemical mass ratios. Another class of somewhat 

 similar compounds has been discovered, which are quite analo- 

 gous to the ordinary hydrates, and to these the name sub 

 cryohydrates has been given. Metallic alloys are true homo- 

 logues of the cryohydrates ; the ratios in which metals unite to 

 form the alloy possessing the lowest melting-point are never 

 atomic ratios, and when metals do unite in atomic ratios the 

 alloy produced is never eutectic, i.e., having a minimum solidify- 

 ing point. Thus pure cast-iron is not a carbide of iron, but an 

 eutectic alloy of carbon and iron. Similar hyperchemical mass 

 ratios are found to exist amongst anhydrous salts ; when one 

 salt fused fir se acts as a solvent to another salt, forming cutcctie 

 salt alloys, similar to ff/teVjV metallic alloys and the cryohydrates. 

 The study of solution aftbrds other instances of masses of unlike 

 matter dealing critically with one another when not in any in- 

 tegral ratio of their molecular masses. Liquids, unsuspected of 

 having chemical or physical lelationships, are found, when 

 mixed with one another, either to get warm and finally lose 

 volume, or get cool and gain volume. In the first place che- 

 mical union is supposed to take jjlace, and it appears ceri.Tin 

 that chloroform unites chemically with alcohol, ether with amyl- 

 ene, and benzene with ether, forming bodies analogous to the 

 sub-cryohydrates and their prototype the sub-cryohydrate 

 CjHgO -I- 4H„0. The examination of those cases in which 

 expansion and cooling results from admixture, shows that the 

 maximum effects are produced when the admixture takes place 

 in certain simple molecular weight ratios. This the author pro- 

 poses to call the maximum molecular repulsion, which, in the 

 case of carbon disulphide and chloroform, is attained with a 

 mixture in which the molecular ratios are a-^ I : i. Mixtures in 

 these proportions are found to show abnormally high vapour- 

 tensions. And the author has made experiments which appear 

 to show that, when carbonic acid and hydrogen are mixed, the 

 joint volume is measurably greater than the sum. 



On the Evidence Deducible from the Study of Salts, by 

 Spencer Umfreville Pickering, M.A. — In this paper the author 

 deals with the evidence as to the molecular weights of salts, 

 derived from a study of the composition (i) of hydrated salts : 

 (2) of basic salts ; (3) of double salts. lie also criticises the 

 evidence deducible from experiments on hydration, dehydration, 

 and the vapour tension of hydrated i-alls, and finally examines 

 the conclusions drawn from the c.olorimetric investigations of 

 such compounds. The conclusions arrived at by the author are 



that, although in a few isolated cases the molecular weights ob- 

 tained would appear to be greater than the analytical results 

 necessitate, still, in a vast majority of cases there are no grounds 

 for multiplying these weights, and indeed there is a considerable 

 mass of evidence in favour of adhering to the simplest possible 

 formula;. Such a conclusion may, at first sight, appear opposed 

 to conclusions drawn from other sources. On the one hand the 

 author considers it undeniable that if we succeed in determining 

 the number of replaceable portions of the elements in any com- 

 pound, we determine ex hypothesi the number of atoms in the 

 molecule, that is, the molecular weight ; and whilst the data at 

 our disposal at present are of the most meagre description, 

 nevertheless a,re such as seem to point to the simplicity of these 

 molecules. On the other hand, considerations based on the 

 crystalline form and other physical properties of bodies force on 

 us the conclusion that liquid and solid molecules are in all 

 probability of a very complicated nature, certainly more com- 

 plicated than gaseous molecules. Both these conclusions the 

 author considers to be reconcileable with one another and con- 

 tends that because the smallest particle of a substance which 

 enters into a chemical reaction may be simple, there can be no 

 reason why many of these particles may not agglomerate and act 

 in unison as regards certain physical forces. That this agglom- 

 erate does not act as a unit towards chemical forces would 

 simply imply that the force which unites the individuals consti- 

 tuting it is not chemical force, or is chemical force of such a 

 weak nature that, in presence of the strong chemical agents we 

 make use of, it is inappreciable. The molecule of a chemist is 

 not necessarily identical with the molecule of the physicist. 



On the Molecular Weights of Solids and Salts in Solution, by 

 Prof. W. A. Tilden, D.Sc, F.R.S. — Accepting the conclusion 

 that bodies in the solid state consist of units or molecules of a 

 very complex character, and made -up of a number of such 

 smaller aggregates as compose the molecules of gases, the 

 author is inclined to go further, and sees no reason for limiting 

 the number of small molecules, which may thus be bound 

 together to form a physical unit. From the law of Duloug and 

 Petit, and of Neumann's law, it would appear that in solid ele- 

 mentary bodies, and in salts, &c. , there is n.) difference between 

 molecule and mass, and that the physical unit is the atom. The 

 facts known concerning specific volumes and refraction equi- 

 valents support such a conclusion. According to this view solid 

 bodies are composed of atoms, which are only distributed into 

 molecules capable of independent existence ; when the body 

 becomes a fluid. Such a view implies that chemical combina- 

 tion between atoms and the combination of molecules which 

 ensues when a gas or liquid returns to the state of a solid are 

 phenomena of the same nature, which agrees with the commonly 

 recognised resemblance between the process of dissociation and 

 those processes of fusion and evaporation. Another consequence 

 of this view is that the idea of limited valency must be confined 

 to gaseous substances. With regard to solutions, many facts 

 are known, which indicate that the molecules of dissolved sub- 

 stances are smaller than those of solids. With regard to the 

 question of water of crystallisation, the author does not alto- 

 gether agree with the views of Dr. Nicol (see Report on Solution, 

 Nature, vol. xxxii. p. 529), but considers that the composition 

 of the salt molecule in solution is dependent chiefly upon tem- 

 perature, and in such a way that the dissolved molecule retains 

 the same amount of water as the crystals formed at the same 

 temperature. As the temperature rises these molecules undergo 

 a gradual dissociation, and at a certain temperature the salt 

 molecules lose this water and become anhydrous. 



On the Alolccular Constiiiition of a Solution of Cobaltous Chlor- 

 ide, by Prof. W. J. Russell, Ph.D., F.R.S.— A thin layer of 

 cubaltous chloride gives an absorption spectrum consisting of 

 two broad, ill-defined bands. If the chloride be mixed with 

 potassium, sodium, or calcium chlorides, the spectrum of these 

 mixtures, both in the solid and fused state, is ditferent from that 

 of cobaltous chloride, and consists essentially of four bands, two 

 of which are marked and characteristic. This same spectrum is 

 obtained with solutions of cobaltous chloride in absolute alcohol, 

 in amyl alcohol, in hydrochloric acid, or in glacial acetic acid. 

 This spectrum would, therefore, appear to be that of cobaltous 

 chloride in an altered molecular state. The spectrum of an 

 aqueous solution is again different, and consists of one broad 

 band nearer to the blue end than the other bands, but the addi- 

 tion of cobaltous chloride to such a solution, or of such bodies as 

 ].iossess an affinity for water, causes a reversion of the spectrum 

 to that of the anhydrous cobaltous chloride. Heat also produces 



