7^ Prof. H. E. Armstrong on Low-Temperature Research 



Calorimetric Studies. 



Eeference was made, under this heading, in mj previous essay, to 

 liquid air and liquid hydrogen calorimeters and several examples 

 were given of the use that had been made of them. In the present 

 septennate, Sir James Dewar has made the liquid hydrogen calorimeter 

 an instrument of precision and has used it in determining the specific 

 heats, at about 50° absohite, of most of the elementary substances 

 and of a large ,numl)er of organic compounds. The instrument is. 

 fully described and figured in the abstract of the discourse delivered 

 on January 23, 1914. In using it, the weighed substance is cooled 

 in boiling nitrogen and afterwards dropped into an insulated calori- 

 meter containing liquid hydrogen ; the evaporated hydrogen is then 

 collected and measured. 



The results obtained with " elementary substances " are of an 

 unexpected character. When the heat capacities of quantities corre- 

 sponding to the atomic weights— in other words, the atomic heats — 

 of the elements are compared, in the case of the metals, a nearly 

 constant value approximating to six is found ; the solid non -metallic 

 " elements " alone give irregular and far lower values. 



On the other hand, when the volumes occupied by atomic pro- 

 portions — the atomic volumes — are contrasted, again at ordinary 

 temperatures, the values rise and fall in periods in a most striking 

 way, corresponding " elements " of the several families occupying 

 corresponding positions in successive periods. 



Sir James Dewar's atomic heat values at very low temperatures 

 (50" abs.) are related in this latter manner, that is to say, the relation- 

 ship resembles that in which the elementary atomic volumes deter- 

 mined at atmospheric temperatures are related. This remarkable 

 relationship is shown in the accompanying curve (Fig. 5) : — 



Such a result, it may be mentioned, had been in part foreshadowed 

 as a consequence of certain modern speculations on the structure of 

 atoms. On this account, the observations are of singular importance. 



A detailed study of the specific heat of sodium in particular, at 

 various temperatures, has been made by Principal Griffiths, which is 

 of special interest in view of Sir James Dewar's results. The recent 

 lecture by Mr. Jeans should also be read in this connexion. 



The so-called elements, it is well known, are now no longer 

 regarded as simple, since the discovery of radium and other radio- 

 active materials. 



It may be noted that chemists have long looked forward to such 

 a development. 



Thus I may quote the following statement made by myself, in 

 submitting a new scheme which I have suggested for the " Classi- 

 fication of the Elements," as recently as March 1902, though I 

 have had the conception in mind since I became aware of the great 



