36 



KNOWLEDGE & SCIENTIFIC NEWS. 



[Mar., 1904. 



osmotic pressure which is produced at a certain tempe- 

 rature and volume by a given weight of the substance. 



If we apply this method to the determination of mole- 

 cular weights of substances in water solutions, it is found 

 that, although most of the organic (and some inorganic) 

 compounds give perfectly normal results — (results, that 

 is, which agree with vapour density determinations and 

 with general chemical considerations) — most salts, acids, 

 and bases give results which are apparently abnormal, 

 the osmotic pressure produced being too high. A dilute 

 solution of potassium chloride, for example, gives an 

 osmotic pressure almost exactly double of that to be 

 expected by the application of Avogadro's hypothesis. 

 That is to say that one molecular weight of potassium 

 chloride gives twice the osmotic pressure which one 

 molecular weight of sugar (urea, &c.) gives under the 

 same conditions. 



It was suggested that this result might be explained 

 by supposing that the salt is " hydrolysed " by the 

 water — i.e., that caustic potash and hydrochloric acid are 

 produced. Since they would be formed in exactly equi- 

 valent quantities, it would not, of course, be possible to 

 detect their presence by the ordinary tests. But such an 

 explanation will not account for the fact that hydrochloric 

 acid itself behaves " abnormally " also, giving about 

 double the expected effect. 



The theory of Arrhenius not only accounts for all these 

 "abnormalities," but offers in addition a most elegant 

 explanation of a large number of facts in connection with 

 the behaviour of salts and other substances in solution, 

 including the phenomena of electrolysis. This theory 

 assumes that most salts, and the strong acids and bases, 

 are largely if not entirely dissociated when dissolved in 

 water (and in some other solvents) into constituent parts 

 or " ions," and that these ions differ from the same sub- 

 stances, as we know them in the separated state, in that 

 they are associated with enormous electric charges. A 

 molecule of potassium chloride, for example, dissociates 

 into an atom of potassium associated with a positive 

 charge, and a chlorine atom with an equal and opposite 

 negative charge. These charges are given up at the 

 respective electrodes when the salt is electrolysed and 

 the potassium and chlorine are obtained in their ordinary 

 " neutral " state. 



A revolutionary hypothesis of this kind was viewed, 

 perhaps naturally, in the first instance with suspicion and 

 dislike, and even at the present day it is not quite univer- 

 sally accepted, but the active opponents, at any rate those 

 who have the courage of their opinions, are becoming 

 daily few and far between. The application of 

 this ionic dissociation hypothesis in explaining various 

 well-known chemical phenomena is an extremely fasci- 

 nating study and it is proposed to give various examples 

 in illustration of the application at a future time, fust 

 one may be mentioned here in conclusion. 



A question which agitated the minds of chemists for a 

 great number of years was of the following form: What 

 happens when two different salts— say, sodium chloride 

 and potassium nitrate— are mixed together in aqueous 

 solution ? Do they remain as they are or do they " change 

 partners," forming sodium nitrate and potassium chloride? 

 A large number of experiments were made with a view of 

 throwing light upon this question, but in most cases the 

 problem appeared to be incapable of solution. It was 

 apparently of no use to attempt the isolation of the differ- 

 ent salts since the equilibrium would be disturbed by their 

 removal, and it seemed only admissibletn employ methods 

 which required no removal from or addition to the solution. 

 Attempts were made, for example, to throw light upon 

 the problem by observing the thermal, volume, or colour 



changes which occurred on mixing the solutions, and 

 although a certain amount of information was gained by 

 such methods, they were in most cases anything but con- 

 clusive. 



This much-debated question then — which metal is 

 united with which acid-radicle ?— is (as a general case in 

 dilute aqueous solutions) now at once disposed of by 

 the ionic dissociation hypothesis, which gives the answer 

 — No metal is united to any acid-radicle ! 



Wind-Driven Electricity 

 Works. 



l>y Dr. Ali-red Gradenwitz. 



Professor Latour, of the Askov Popular Academy 

 (Denmark), has for some years b^en engaged on behalf 

 of the Danish (jo\'ernment in investigating the problem of 

 utilising wind power in connection with small electricity 

 works. If, however, the dynamo be direct-coupled to the 

 wind motor, the results obtained are unsatisfactory on 

 account of the exceedingly variable speed of the wind. As 

 pointed out in an address recently delivered by Professor 

 Latour before the Copenhagen Technical and Hygienic 

 Congress, he was met with difficulties in designing a suit- 

 able regulator for controlling the speed of the dynamo. 

 At present, however, these difficulties appear to have 

 been overcome, and an electricity central station near 

 Askov has been worked with wind power for a year with 

 satisfactory results. 



The arrangement of a similar electricity works is repre- 

 sented diagrammatically in fig. i. The regulating device 

 itself is made up of two different parts. The mechanical 

 regulating device is intended for maintaining at constant 

 values the peripheric force transmitted to the belt disc of 

 the dynamo. The two belt discs R R are mounted on a 

 movable arm A, bearing a counterweight P. The 

 resulting tension of the belt is thus kept constant, depend- 

 ing on the weight of the belt discs as well as on the counter- 

 weight P. The ratio of the resulting belt tension and 

 the maximum peripheric force susceptible of being trans- 

 mitted by the belts is, however, practically constant. 

 The peripheric force transmitted by the wind motor to 

 the belt disc R accordingly cannot exceed a given value, 

 the torque of the dynamo remaining below a corresponding 

 value. Any surplus energy developed by the wind motor is 

 lost as heat with the friction of the belt. A constant torque 

 of the dynamo axle will, however, correspond with a 

 constant current intensity in the armature. In the case 

 of the magnetising intensity employed, the load is in fact 



Fig. I. 



