904 



is supposed, which is determined according to the quantum-theory. 



In the extreme form of this type no other suppositions are intro- 

 duced than those of the quantum-theory. There is naturally room for 

 transitional forms between this extreme form and the other type of 

 hypothesis. These are got by assuming polymerisations or a mole- 

 cular tield besides the quantum-theory. 



It is now of importance, not only for magnetism, but also for the 

 law of molecular activity in general, to decide between these two 

 different types of hypothesis, by experiment. The most important for 

 this purpose are experiments in which the paramagnetic molecules 

 are brought to different distances from each other. For if the above 

 mentioned question should be answered in the negative and it should 

 be proved that the susceptibility per molecule remained the same 

 at whatever distance they are from each other, then all hypo- 

 theses of the first sort (mutual influences) would of course fall to 

 the ground. The measurements which shoidd demonstrate this woidd 

 be an experimentum crucis. 



The determination of the susceptibility of liquid mixtures of oxygen 

 and nitrogen claims the first place in experiments upon the influence 

 of the distance of the molecules upon the deviations from Curie's 

 law\ The liquid (paramagnetic) oxygen exercises no chemical influence 

 whatever upon the liquid (diamagnetic) nitrogen; the two substances 

 can be mixed in any proportions, so that the distance of the para- 

 magnetic oxygen molecules can be increased at pleasure : the mixtures 

 remain moreover liquid down to a \ery low temperature, which is 

 of particular importance, if the theory of quanta is to be applied. 

 Experiments with these mixtures promised therefore a more distinct 

 and more immediate decision than those with crystals and solutions 

 of chemical compounds in different degrees of dilution '). In the 

 investigation now completed we have not been able to do more 

 than make a first survey of the difficult tei-ritory. 



We here offer our sincere thanks to Dr. Oosterhuts, who has con- 

 tributed greatly to the success of our work, by very carefully measuring 

 out the field that served for our experiments, and by repeating certain 

 susceptibility determinations which were doubtful. His measurements 

 enabled us to introduce important corrections in our results. 



1) With regard to these we may remark that the important investigations by 

 Cabrera and Moles (Arch. d. Geneve (4) XXXV, May 1913) of solutions of iron 

 salts are of a chemical nature and assum.e the validity of Curie's law. Their object 

 is therefore quite different from ours, in wliich the point is to investigate the influence 

 of the distance of the molecules of a chemical element dissolved in another element, 

 upon a function of the temperature. 



