Chemistry and Physics. 147 



The book gives an excellent impression in regard to its clear 

 presentation of the subject in an elementary way. Withont 

 doubt it might be used to advantage by many of those engaged in 

 coal mining in the United States, for the differences in technical 

 terms, mining regulations, and weights and measures in England 

 and this country world be of little importance in a book devoted 

 chiefly to scientific instruction. h. l. w. 



5. The Adsorption of Gas oy Charcoal and Silica. — The exten- 

 sive application of the phenomenon of adsorption of gases by 

 charcoal in the construction of masks for protection from noxious 

 gases, and for the reduction of pressure at liquid air temperatures 

 in evacuated vessels has greatly stimulated research upon the 

 nature of the process. An investigation by Professor Henry 

 Briggs recently published had for its main object the discovery of 

 a non-inflammable substitute for activated charcoal but the results 

 are also important from his consideration of the theoretical 

 aspects of the phenomenon. 



The gases used were nitrogen and hydrogen and out of a large 

 number of non-inflammable substances tried a dried and granular 

 silica gel prepared from water glass was found to be the best. 

 Its capacity for nitrogen at 190° C. and at atmospheric pressure 

 was found, on the volumetric basis, to be greater than that of the 

 best charcoal by 66 per cent. Both of these substances showed 

 preferential adsorption for nitrogen and hydrogen and exemplify 

 the influence of chemical composition upon the phenomenon. 



In any sample of granulated charcoal or silica the author 

 regards the gross volume to be made up of : (a) the volume of the 

 solid matter, (b) the interstitial volume i. e. of the open spaces or 

 voids between the grains, (c) the internal gaseous volume which 

 is made up of the volume of the capillaries or polymeral inter- 

 stices within the granules themselves. A rough estimate indicates 

 that these volumes constitute 27, 31, and 42 per cent of the whole 

 in activated charcoal or silica but have the relation 51, 6, 43 per 

 cent in de-activated silica. The author is of the opinion that in 

 considering the intrinsic nature of adsorption we have not to do 

 with the ultimate molecule of the solid but with elaborate poly- 

 mers. The degree of canalization of the substance both on the 

 microscopic and the molar scale is important but these passages 

 are of use only when they traverse a medium which is in proper 

 physical condition. For a high capacity silica when de-activated 

 has no adsorbing power although it still retains one-fifth of its 

 original internal gaseous volume, and on the other hand pow- 

 dered graphite which has no capillary passages shows consider- 

 able adsorbing power. It is to be inferred that the connecting 

 passages serve to distribute the gas but that it is held chiefly on 

 the surfaces of polymers in the openings of molar dimensions. 

 On this view any treatment which would disrupt the elaborate 



