132 



THE POPULAE EDUCATOR 



It appears to him that the old habit of self-devotion to high 

 purposes is dying out, and that it is his task to re-awaken it. He 

 will ride in quest of adventures. He will deliver distressed 

 ladies, chastise and humble tyrants, break up wicked enchant- 

 ments, slay dragons, and griffins, and other terrors of the earth. 

 He will be the champion of Christendom against the Moslem 

 and the infidel. Let it be observed that there is a noble as 

 well as a ludicrous side to this conception of the mad knight 

 for crazed he assuredly is. The thoughtful reader will even 

 find a touch of pathos in the strange, distraught, fantastic 

 figure the pathos of an unfulfilled ideal, of illusions shattered. 

 The aims of Quixote are high and magnanimous, but his mind 

 is out of joint with facts. 



Sancho Panza is a character admirably contrasted with that 

 of the Don, whom he serves as a squire. His gross, sensual, 

 prosaic nature is the exact opposite of the dreamy, imaginative, 

 self-sacrificing disposition of his master. Faithful he is, with 

 touches of homely affection ; yet his great idea is to benefit him- 

 self, and to get something substantial for his pains. In the 

 matter of the governorship of Barataria, he is as much be- 

 fooled as Quixote himself ; but the motive is sordid. Usually, 

 however, he sees through the delusions of the knight, and cor- 

 rects them with shrewdness and native sense. He has at his 

 command an exhaustless stock of proverbs, embodying in the 

 briefest compass the mother- wit of Spanish peasants; and 

 altogether he is one of the most amusing fellows in fiction. The 

 other characters in the book are less strongly marked, but show 

 the hand of the master. The first portion of this wonderful 

 work was published in 1605 ; the second in 1615. It has been 

 said that the earlier part was written when the author was in 

 prison for debt ; but the tradition is very doubtful. The life 

 of Cervantes, however, was chequered ; his fame alone stands 

 high above the accidents of the world. 



LESSONS IN CHEMISTRY. V. 



OXYGEN. 

 SYMBOL . . O ATOMIC WEIGHT . .16 DENSITY 



16. 



THIS, the most widely-spread, and the most important of all 

 the elements, was discovered independently by Priestley and the 

 Swedish chemist Scheele, in 1774. 



It constitutes 1 of the atmosphere, f of the weight of water, 

 and at least of the materials composing the solid crust of the 

 earth. It is a tasteless, colourless, inodorous gas. 



TO PREPARE OXYGEN. 



It cannot be got from the air very readily ; for we are not 

 acquainted with any re-agent which will absorb the nitrogen with 

 which it is associated ; yet there are substances which will com- 

 bine with oxygen at cer- 

 tain temperatures, and 

 again give it off at other 

 temperatures. If, for 

 example, humid air 

 be passed through a 

 porcelain tube containing 

 baryta (BaO), this oxide, 

 when heated to a low red- 

 heat, will become the per- 

 oxide (BaO 2 ) that is, the 

 highest oxide not exhibit- 

 ing acid qualities ; when 

 strongly heated it gives 

 off the oxygen again, 

 and returns to its former 

 state (BaO). 



Melted silver has also 

 the property of absorb- 

 ing oxygen from the air, 

 which it gives off as it 



returns to the solid state. It need not be said that these 

 methods of obtaining oxygen from the atmosphere are neither 

 easy nor inexpensive. 



1. The most simple of all methods of obtaining this gas 

 would appear to be by heating the oxides of the noble metals. 

 Such metals are "' those which can be reduced from their oxides 

 by heat." If we heat to any temperature, or for any length of 



Fig. 14. 



time, some iron-rust, which is the oxide of that metal, we shall 

 never be able to drive off the oxygen and leave the pure iron 

 behind ; but if we heat the oxides of gold, silver, platinum, or 

 mercury, the heat will be sufficient to overcome the affinity 

 which unites the gas and the metal the former will escape and 

 the latter remain. We do not advise the student to attempt to 

 collect oxygen by this means, for more heat is required than is 

 given by a spirit-lamp ; but the experiment may be successfully 



Fig. 15. 



shown, as in Fig. 14. With the red oxide of mercury (HgO) 

 in the test-tube put a piece of charcoal ; the oxide will give 

 off the oxygen, the charcoal will burn brightly, and globules of 

 mercury will be found at the bottom of the tube. Fig. 15 shows 

 convenient forms of clips for holding test-tubes; A can be made 

 by the student ; s is an india-rubber strap ; w, a piece of wood 

 which serves the purpose of a hinge. 



2. The more general way is by heating in a Florence flask potas- 

 sium chlorate (KC1O 3 ). By adding one-third its weight of the 

 black oxide of manganese (Mn0 2 ), the gas will come off at a lower 

 temperature; the manganese itself undergoes no change, but 

 acts by its presence : this phenomenon is called catalysis. The 

 red oxide of iron (Fe 2 O 3 ), the black oxide of copper (CuO), or even 

 sand, has the same effect, though not in so eminent a degree. 



The apparatus is arranged as in Fig. 16. The stand is con- 

 venient, but superfluous, as the flask may be held by a clipper, or 

 a piece of paper, as the test-tube in Fig. 14. Instead of making 



Fig. lb. 



bends in the glass tubing, it is as well to have a short piece of 

 small india-rubber tubing to join the tube from the cork and the 

 delivery-tube, thus forming a flexible bend. A bowl is filled with 

 water, and the jar into which the gas is to be received is laid down 

 in it ; when in this position it must be covered completely by the 

 water, and there must be left in it no air-bubbles. Now raise it 

 up, mouth downwards, but not out of the water, so that the jar 

 will be full of water so long as its mouth is below the surface. 



Should there not be a bowl at hand deep enough to allow the 

 jar to be completely covered when lying down, a shallow dish 

 may be used. In this case the jar must be filled with water nntil 

 it runs over the brim ; then place over the mouth a piece of glass 



