717 MOLECULAR ATTRACTION MOLECULAR THEORY. 



MOLYBDENUM. 



718 



Nearly all the molasses made in the English sugar colonies was 

 formerly converted into mm by fermentation and distillation on the 

 estates ; but the price of that spirit haying declined , and improvements 

 having been made in the processes of refining sugar in Europe, whereby 

 a large proportion of West Indian molasses has been rendered crystal- 

 lisable, a considerable and continually increasing quantity of molasses 

 is shipped for that purpose. The syrups, which ultimately remain in 

 a liquid form after passing through the processes of a refining-house, 

 whether the same are the produce of Muscovado sugar or of molasses, 

 are sotnetiines called molasses, but are more generally known as treacle. 

 The imports of molassess, which were only 40,000 cwts. in 1820, rose 

 to 250,000 cwts. in 1830 ; in 1845 they were more than 500,000 cwts. ; 

 and in the 14 years thence to 1859, they varied from about 600,000 to 

 1,100,000 cwte. 



MOLECULAR ATTRACTION MOLECULAR THEORY. In 

 chemistry it is conceived that bodies are made up of indivisible atoms, 

 each having a definite uniform weight and a general character. The 

 service that this theory has rendered to science may be seen by con- 

 sulting ATOMIC THEORY. The ultimate particles of matter are termed 

 atoms, the word molecules being applied to the constituent or hetero- 

 geneous whole. [MOLECULE.] If the molecular constitution of bodies 

 were known, that is, the specific nature of these molecules, and the 

 laws of the forces which retain them in connection, whether these 

 forces be of attraction or repulsion, science would then be able to 

 define the changes and sequences of the material universe. Various 

 efforts have been made from time to time to construct theories on this 

 ground sufficiently general to afford a basis for important and wide con- 

 clusions, and yet to avoid injurious restrictive conditions. According 

 to the theory of Boscovich, matter does not consist of solid particles, 

 but of mere mathematical centres of force. Each body is supposed to 

 be made up of a number of geometrical points, from which emanate 

 forces following certain mathematical laws, in virtue of which the 

 forces become at certain small distances attractive, at certain other dis- 

 tances repulsive, and at greater distances again attractive. [ATTRACTION.] 

 " From these forces of the points arise the cohesion of the parts of the 

 same body, the resistance which it exerts against the pressure of another 

 body, and, finally, the attraction of gravitation which it exerts upon 

 bodies at a distance." 



Dr. Whewell, from whom we have just quoted (' History of Scientific 

 Ideas,' vol. ii., 1858), regards this theory as homogeneous and consistent, 

 and thinks it probable that it may be used for investigating and express- 

 ing true laws of nature, although the attempt to identify the forces by 

 which the particles of bodies are bound together with mechanical 

 attraction appears to be a confusion of two separate ideas. This 

 theory, he remarks, " may be so conceived as possibly to involve an 

 explanation of all the powers which their parts exert (such powers, 

 namely, as those which produce optical, thermotical, and chemical 

 phenomena) ; but this theory cannot supply an explanation of the 

 mechanical properties of a body as a whole, especially of its inertia. A 

 collection of mere centres of force can have no inertia. If two bodies 

 are considered as two collections of centres of force, the one attracting 

 the other, there is in this view nothing to limit or determine the 

 velocity with which the one body will approach the other. A world 

 composed of such bodies is not a material world ; for matter implies 

 not only force, but something which resists the action of force." 



Representing matter as a collection of molecules or centres of force, 

 modern chemists have used the molecular hypothesis as a basis for 

 calculations respecting the elementary forces of bodies, supposing the 

 i ties of bodies to depend upon forces emanating from immovable 

 points of their mass. The mechanical philosopher, also, thus treats 

 the properties of bodies on a small scale as Newton had already done 

 with central forces on a large scale. Newton himself remarks, in the 

 preface to his ' Principia,' " Many things induce me to believe that the 

 rest of the phenomena of nature, as well as those of astronomy, may 

 depend upon certain forces by which the particles of bodies, in virtue 

 of causes not yet known, are urged towards each other and cohere in 

 regular figures, or are mutually repelled and recede ; and philosophers 

 knowing nothing of these forces have hitherto failed in their exami- 

 nation of nature." Laplace, following up this hypothesis, has shown 

 its value, if we suppose the forces exerted by the particles to decrease 

 so rapidly with the increasing distance from them that the force is 

 finite only at distances imperceptible to the senses, and vanishes at all 

 remoter points. " He hag taught the method of expressing and calcu- 

 lating such forces ; and he and other mathematicians of his school have 

 applied this method to many of the most important questions of 

 physics, as capillary action, the elasticity of solids, the conduction and 

 radiation of heat. The explanation of many apparently unconnected 

 and curious observed facts by these mathematical theories, gives a 

 trong assurance that its essential principles are true. But it must be 

 observed that the actual constitution of bodies, as composed of distinct 

 and separate particles, is by no means proved by these coincidences. 

 The assumption , in the reasoning, of certain centres of force acting at 

 a distance, is to be considered nothing more than a method of reducing 

 to calculation that view of the constitution of bodies which supposes 

 that they exert force at mnj point. It is a mathematical artifice of 

 the same kind as the hypothetical division of a body into infinitesimal 

 parts in order to find its centre of gravity, and no more implies a 

 physical reality than that hypothesis does." Dr. Whewell, to whom 



we owe this quotation, refers also to Poisson's views of capillary action, 

 and also to Wollastou's attempt to bring the doctrine of ultimate atoms 

 to the test of observation in the case of the ATMOSPHERE, under which 

 head some notice of Wollaston's argument will be found. But we may 

 here remind the reader of Wollaston's conclusion that the observed 

 phenomena accord with the supposition that the earth's atmosphere is 

 of finite extent, limited by the weight of ultimate atoms of definite 

 magnitude, no longer divisible by repulsion of their parts. We must, 

 however, refer to Dr. Whewell's work for his objections to this line of 

 reasoning, and conclude by naming the most important works which 

 have of late years assisted the molecular theory, such as Gauss on 

 ' Terrestrial Magnetism ; ' Ohm's ' Contributions to Molecular Physics,' 

 in which he supposes that the ultimate molecules of matter have both 

 simple and polar powers, and by means of this hypothesis he attempts 

 to form a complete system from which the phenomena of light, heat, 

 and electricity necessarily arise ; Mr. Grove's work, ' On the Correlation 

 of the Physical Forces,' is also in the same direction. 



MOLECULE. Matter is supposed to be made up of indefinitely 

 small particles or molecules, which in a simple substance are called 

 integrant, or homogeneous, and in a compound, constituent or hetero- 

 geneous. 



MOLECULES. The smallest indivisible quantities of matter which 

 take part in chemical re-actions. [ATOMIC WEIGHTS; CHEMICAL 

 EQUIVALENTS.] 



MOLYBDENUM (Mo). A rare metal, occurring native chiefly as 

 the bisulphide, a mineral that, in appearance and properties, so much 

 resembles graphite as to have been mistaken for that substance until 

 the year 1778, when its peculiarity was first pointed out. A descrip- 

 tion of the two or three ores of molybdenum that have hitherto been 

 discovered will be found in the NATURAL HISTORY DIVISION, article 

 MOLYBDENUM. The method of isolating the metal from the sulphide 

 is also there detailed. The equivalent of molybdenum is 46. 



Molybdenum and oxygen form three compounds : 



1. Protoxide of molybdenum MoO 



2. Binoxide of molybdenum . . . . . MoO a 



3. Molybdic acid MoO 3 



1. Protoxide of Molybdenum (MoO). Molybdous oxide. Obtained in 

 the anhydrous form by the action of nascent, hydrogen, and in the 

 hydrated condition on adding ammonia to a solution of the proto- 

 chloride. In the latter state it is soluble in solution of carbonate of 

 ammonia but not in the carbonates or hydrates of potash or soda. 

 Both varieties are of a black colour. 



2. Bivoxide of Molybdenum (MoO,,). Molybdic oxide. Formed when 

 molybdate of ammonia is strongly ignited in a covered crucible. The 

 residue should be washed with caustic potash to remove any molybdic 

 acid. Its colour is usually dark brown, but purple in direct sunshine. 

 It is to a certain extent soluble in water; the solution sometimes 

 gelatinises spontaneously. The salts of bihoxide of molybdenum are 

 red when hydrated, but in the anhydrous state are almost black. An 

 olive green oxide, and a blue oxide of molybdenum have been described, 

 but they are now known to be mixtures of the binoxide with molybdic 

 acid. 



3. Molybdic acid (Mo0 3 ), is generally obtained by roasting the bisul- 

 phide, at a low red heat, in clay basins, but M. Brunner recommends 

 that the pulverised mineral should be first mixed with an equal volume 

 of quart/ose sand, and the mass then roasted in a platinum capsule 

 until it has acquired a lemon-yellow colour. After cooling, the 

 molybdic acid is extracted by exhausting the product with ammonia. 

 The residue from the evaporation of the ammoniacal solution is heated 

 to low redness to expel ammonia, when molybdic acid remains as a 

 pale buff-coloured powder. At a very high temperature molybdic acid 

 volatilises and condenses on cool surfaces in brilliant transparent 

 needles. Molybdic acid combines with bases to form neutral and acid 

 salts called mulybdates. 



Molybdate of ammonia is sometimes used for detecting and even 

 estimating phosphoric acid. It is best prepared by dissolving, with the 

 aid of a gentle heat, two parts of pure molybdic acid and one of 

 tartaric acid in fifteen of water and afterwards adding ten parts of 

 ammonia (sp. gr. 0'97) and fifteen of nitric acid. The whole is heated 

 to ebullition in a porcelain basin, when about one fifteenth of the 

 molybdic acid will precipitate, and must be separated by filtration. 

 The solution is then ready for detecting phosphoric acid, with which 

 it gives a yellow crystalline precipitate of phospho-molybdate of 

 ammonia. 



Molybdenum and sulphur combine in three proportions and form 

 bisulphide of molybdenum, (MoS ) already noticed ; tersulphtde <>f molyb- 

 denum, or sulpho-mohibdic acid, (MoS s ) precipitated on adding hydro- 

 chloric acid to a solution of a molybdate saturated with sulphuretted 

 hydrogen; and quadrisulphide of molybdenum or pertnlpho-mulijbdic, 

 acid, (MoS,). Sulplio-molybdate of potash (KS,MoS 3 ) crystallises ill 

 magnificent iridescent crystals. 



Muli/bdenum and chlorine form two distinct chlorides, namely, proto- 

 chloiidi and bichloride, as well as several oxychlorides that appear to 

 contain terchloride of molybdenum. 



Pntochloride of molybdenum (MoCl). Excess of hydrochloric acid 

 is added to a concentrated solution of an alkaline molybdate and zinc 

 theu introduced. AB soon as evolution of hydrogen commences, the 



