at the Royal Institution, 1 900-1 907. 855 



them. The first septenate may be termed the Hydrogen jjeriod * ; 

 the second the Charcoal Vacuimi period. The discovery of the 

 marvellous power of charcoals to absorb gases at low temperatures 

 will render this latter period ever memorable. 



The reduction of helium from the gaseous state became practic- 

 able only when this discovery was made, but to utilise such a new 

 appliance fully was not easy ; naturally others have entered the 

 field meanwhile and success has fallen to those who have completest 

 •command of the necessary appliances and the ample funds, as well as 

 the skilled assistance, required for the rapid prosecution of such work. 



The Use of Charcoal in the Production of High Vacua. 



Charcoal, it has long been known, even under ordinary con- 

 ditions, has the power of absorbing gases and vapours, often in 

 considerable proportions ; it is noteworthy also that it is commonly 

 used in depriving liquids of colour — on a very large scale, for 

 example, in purifying sugar. The desire to explain its absorptive 

 power has given rise to much experimental inquiry ; indeed, of late 

 years, the property which charcoal possesses, in common with many 

 other materials in a fine state of division, including soils, of with- 

 drawing substances from solution has been the subject of many 

 discussions. 



In sketching the history of the subject in 1905, Sir James Dewar 

 pointed out that speculations on the porosity of matter date back 

 several centuries. He drew attention to the following significant 

 passage in a discourse published in 1684 by Boyle and entitled 

 " Experiments and Considerations about the Porosity of Bodies " : — 



" When I consider how much most of the qualities of bodies and con- 

 sequently their operations depend upon the structure of their minute and 

 singly invisible particles and that to this latent contexture, the bigness, 

 the figure and the collocation of the intervals and pores do necessarily 

 concur with the size, shape and disposition or contrivance of the sub- 

 stantial parts, I cannot but think the doctrine of the small pores of 

 bodies of no small importance to Natural Philosophy." 



Modern inquiry has thoroughly justified Boyle's acute surmise 

 that " the quaKties of bodies and consequently their operations " are 

 functions of their latent contexture,t organic chemistry being one 



* It should not be forgotten that the Dewar vacuum vessel came into use 

 during this period and was proved to be indispensable to the successful prose- 

 cution of inquiry at low temperatures ; that period may therefore well be 

 ranked also as the vacuum vessel period. 



t Contexture — " the disposition and union of the constituent parts of a 

 thing with respect to each other : constitution " ; as an apposite expression 

 of internal structure, the term may be preferred to configuration, which is 

 now commonly used. 



2 A 2 



