80 Notes concerning the Phenomena 



" We pump out a portion of the air from the containing 

 vessel, and then the vapours and gases condensed in the 

 pores or on the surface of the balance come into play. 



" And now the question arises whether, by any degree of 

 pumping, even with the aid of dessicating contrivances, 

 such as that employed in the method of Dr. Andrews, we 

 can ever completely rob the surface and pores of a solid body 

 of all vaporizable matter. It is to be remembered that the 

 treating of the pith-ball before the experiment, so frequently 

 described by Mr. Crookes, implies a suspicion of something 

 condensed in its pores ; and the possibility of that some- 

 thing, as fast as it is expelled from the one, being rapidly 

 condensed into the pores of the opposite ball, is too obvious to 

 need remark. Even charring the balls will be accompanied 

 by the formation of tarry matters of various volatility. 



"There is a paper by Mitscherlich, published in the Annates 

 de Chimie et cle Physique, for January, 1843, which has an 

 interesting bearing upon this question. He shows that 

 charcoal has the power of absorbing carbonic acid, and com- 

 pressing it within the pores with such force that it occupies 

 only one fifty-sixth part of its ordinary volume, one-third of 

 this being condensed within the pores in a liquid condition. 

 But it takes 36 "7 atmospheric pressure to liquify carbonic 

 acid. The charcoal then holds the carbonic acid with a grasp 

 equal to 36*7 atmospheres. As the most perfect air pump 

 can only remove the pressure of one atmosphere, how can it 

 be expected to cope with such a force and remove all the gas 

 from the pores of the charcoal ? But this is only one instance 

 of a general property of all porous bodies to condense gases 

 and liquids within their pores. Nor are porous bodies the 

 only ones that possess this power, for it is well known that 

 in some cases solid metals have the property of occluding 

 gases within their substance with stupendous force and with 

 enormous condensing power. We know that these gases can 

 be expelled by ignition, that is to say, by heat, but it is not 

 easy to see how the removal of one atmosphere of pressure 

 from porous or even metalhc bodies, even with accessory 

 dessicating appliances, can remove all vaporizable consti- 

 tuents from their pores or surfaces, which antagonise a force 

 out of all proportion greater than that lifted off by the pump. 

 Mr. Crookes finds the ultraviolet rays to be also capable 

 of producing effects of recession. This I have not put to 

 experiment. But these rays admittedly have the power to 

 shake asunder the constituents of certain chemical com- 



