234 SCIENTIFIC AMUSEMENTS. 



wire and foil being capable of attracting the gases sufficiently 

 vigorously to intensify remarkably their chemical activity. 



Expt. 280. Absorption of Ammonia Gas by Charcoal. To do 

 this successfully, a few pounds of quicksilver are requisite, con- 

 tained in a stout basin ; an ordinary mortar of porcelain answers 

 well. Obtain a stout test-tube and a piece of charcoal that will just 

 go inside ; heat the charcoal in the flame of a Bunsen lamp or spirit 

 lamp for half a minute, and then plunge it (still hot) under the 

 mercury ; the heating expels air from its pores, and the plunging 

 under mercury cools it and prevents its burning away. Fill the 

 test-tube with ammonia gas as in Expt. 75, and then close it with 

 the thumb and bring it to the basin of quicksilver, depressing the 

 thumb and mouth of the tube under the metal so as to prevent 

 air displacing ammonia gas when the thumb is removed. Now 

 insert the piece of charcoal inside the tube, the mouth being still 

 under the quicksilver (fig. 96) ; support the tube by a clamp or 

 holder and leave it to itself for a few minutes ; 

 you will gradually see the quicksilver rise in 

 the tube, the lump of charcoal floating on the 

 top. If the tube was completely filled with 

 ammonia, all air being displaced, the quick- 

 silver will ultimately fill the entire tube; but 

 otherwise a more or less considerable bubble 

 of air will remain unabsorbed. 



The mercury ascends because the charcoal 

 gradually absorbs the ammonia gas, the pres- 

 sure of the atmosphere forcing the mercury up 

 as the absorption proceeds, precisely as water 

 was similarly forced up in the analogous ex- 

 periment (Expt. 76) of dissolving ammonia gas 

 in water. As in that case, too, the experi- 

 ment shows that some gases, e.g., ammonia, are 

 much more readily absorbed or dissolved (both 



b ? P 0rOUS charCOal and ^ Water ) tha11 therS ' 

 such as air. 



Expt. 281. To Cleanse Mercury. When mercury is used for 

 experiments such as the preceding, it often becomes necessary to 

 clean the surface from dust and dirt. One of the simplest 

 methods of doing this is to make a paper filter in a stout glass 

 funnel (Expt. 56), using a piece of thick paper for the purpose ; 

 the dirty mercury is then poured into the paper cone till nearly 

 full, and a fine knitting needle passed downwards through the 

 mercury to the point of the paper cone, so as to make a small 

 perforation ; on withdrawing the needle a fine stream of clean 



