Z INTRODUCTION. 



until a condition of equilibrium is reached. The mixture, being now less associated 

 than its components, should have less dissociating power than the latter, and this is 

 actually the case in every instance studied. Moreover, the lowering of conductivity 

 is more marked when the alcohols are mixed with water than when they are mixed 

 with each other, because they are associated to a less degree than water. 



This conclusion was subsequently confirmed by Jones and Murray. 1 By means 

 of cryoscopic measurements with water, formic and acetic acids, and mixtures of 

 these liquids, they showed that the molecular weights of these substances were 

 always less, even in very concentrated solutions, than the values obtained by Ram- 

 say and Shields, who had found that these liquids are all highly associated in the 

 pure condition. 



Jones and Carroll 2 extended the work of Jones and Lindsay. The solvents used 

 were water, methyl and ethyl alcohols, and various mixtures of these with one 

 another. The electrolytes chosen were cadmium iodide, sodium iodide, calcium 

 nitrate, hydrochloric acid, sodium acetate, and potassium iodide. Cadmium iodide 

 in mixtures of methyl alcohol and water showed no minimum, except in the curves 

 for V = 16, F = 32, and F = 64 at 0. Here a minimum appeared in the 75 per cent 

 mixture. In all cases, however, the conductivities were less than the average values. 

 In mixtures of ethyl alcohol and water, the same salt showed entirely similar phenom- 

 ena, though no minima were observed. Sodium iodide gave a well-defined mini- 

 mum in the 50 per cent mixture of methyl alcohol and water. Calcium nitrate in 

 the same solvents gave no minimum, while the conductivities again did not obey 

 the law of averages. Hydrochloric acid gave irregular results, but a minimum was 

 noticed in a mixture containing 90 per cent methyl alcohol. Sodium acetate in 

 various mixtures of acetic acid and water gave entirely irregular figures. 



An effort was made to determine the dissociating power of the methyl alcohol- 

 water mixtures, since it had been noticed that the molecular conductivity, /x v , for 

 hydrochloric acid became constant at rather small dilutions in these solvents. 

 Limiting values of conductivity were obtained for sodium, potassium, and ammo- 

 nium iodides and bromides, and lithium nitrate, in 50 per cent methyl alcohol. In 

 all these cases the dissociation was complete in the mixture at a dilution considerably 

 less than that necessary cor complete dissociation in water or methyl alcohol. It 

 now remained to find the cause of the minimum. 



Two factors are to be considered amount of dissociation and ionic mobility. 

 The first has been eliminated, hence the minimum must be caused by a decrease in 

 ionic mobility. From the results of various observers, it was found that the vis- 

 cosity of aqueous alcohol in the neighborhood of a 50 per cent mixture is higher 

 than that of either of its constituents. Furthermore, the change in viscosity with 

 increasing content of alcohol is more marked at lower temperatures than at higher, 

 and rise in temperature shifts the maximum in viscosity, or minimum in fluidity, 

 slightly towards the mixture containing the greater percentage of alcohol. These 

 phenomena are closely paralleled by the conductivity minima. The latter all occur 

 in or near the 50 per cent mixtures, and are more marked at than at 25. Cad- 

 mium iodide, for instance, shows a minimum at in three solutions, but none at 25. 



lAmer. Chem. Journ., 30, 193 (1903). /W., 32, 521 (1904). 



