Physics. — "On the diffraction of RönUien-rays in liquids." By 

 Prof. W. H. KiaisoM and Piof. J. Dk Smkdt. (Comrininication 

 N'. 10 from llie Laboratory of Physics and Physical Chemistry 

 of tlie Veterinary College). (Communicated by Prof. H. 

 Kamermngh Onnks.) 



(Communicated at the meeting of March 25, 1922). 



§ 1. Introduction. The investigation by means of Röntgen-rays 

 of the structure of substances that are in liquid or solid stale at 

 temperatures lower than the ordinaiy one, seenjs us to be of extra- 

 ordinary importance. These substances namely belong to those that 

 possess the most simple chemical structure (in the gaseous state 

 several of them are mon- or diatomic). In most cases their molecules 

 consist of light atoms small number of electrons). Therefoi'e the ex- 

 perimental results obtained with these substances will lead more easily 

 than other ones to conclusions' of importance foi' the structure not 

 only of the crystalline state but also of the molecule and the atom. 



We thus gladly followed the invitation of Prof. Kamehlingh Onnes to 

 make such an invesligation on the diatomic elements oxygen, nitrogen, 

 if possible on hydrogen etc. and the monatomic elements as f.i. argon. 

 In the discussion of the scheme for this investigation, for which we 

 made at Leiden some preparatory experiments, the first question 

 was the following: Will liquefied gases also give a diffraction figure 

 when they are crossed by a beam of Röntgen rays as it was the case 

 with the liquids that were investigated by Debue and Scherker^)? 

 As some Rontgen-technical difficulties had to be overcome we 

 agreed to continue the preparatory expeiiments at Utrecht, as far as 

 we should be able to obtain there the liquid gases and work there 

 with them. Some of the results of these experiments will be given 

 in this paper. In these investigations we did not only use liquid 

 oxygen and argon') but also some substances that are liquid at 

 ordinary temperatures. 



^ 2. The apparatus. Fig. 1 shows the vacuum glass g and fixed 



1) P. Debue and P. Scherkeb, Nachrichten Göttingen 1916. 

 '-) The argon was put at our disposal by N.V. Philips' Gloeilampenfabrieken, 

 for which we wish to express here our thanks 



