S14 



CHEMISTRY. 



[OJCIIIBB. 



oxygen. The light will be greatly increased, and the 

 wick will luirn innrli faster than in the i)|x>n air. 



-Blw tint the light of a taper to as 

 n. M. to leave a little of the wick red-hot 

 \VliiUt in this stU> dip it into a j:ir of 

 ,:i 1 it will immediately re-light 

 may be repeated many tunes with 

 -*me jar of gas. The tapers best 

 1 for this experiment are those ued 

 for lighting gas ; but a common tallow 

 answers nearly as well (See 

 Fix. 36). 



i-rrimtnt 11. Tie a small piece of 

 charcoal to the end of a piece of thin brass or copper 

 wire; make the charcoal red-hot, by holding it in the 

 spirit-lamp flame. When red-hot, immerse it in a jar of 

 oxygen; a most beautiful combustion will take place, 

 sparks living off on all sides. Boxwood charcoal answers 

 host for this purpose. 



im'iit 12. Put asmall piece of phosphorus, not 

 larger than a pea, into the phosphorus cup or holder. * 

 IT. Hi-move the glass stopper or cork from one of 

 the jars of gas, and set fire to the phosphorus 

 by means of a taper. Dip the cup into the 

 jar immediately, and a splendid light will be 

 produced. This forms one of the most bril- 

 liant experiments in chemistry. The heat 

 often cracks the jar ; and as there is no sure 

 way of preventing this, we recommend the use 

 of the common preserve or sweetmeat bottle, 

 as being of little cost in case of breakage. Fig. 

 37 shows the method of this experiment. 

 Erptriment 13. Put a small piece of sulphur into 

 another holder, tint lighting it, by heating the cup in 

 the flame of a candle ; introduce it into a jar of oxygen, 

 and a fine blue light will be given out 



The two hut experiments afford instances of the pro- 

 duction of acids by burning the two substances in 

 oxygen. These acids may easily be detected by tasting 

 the water which is left on the aides of the glass whilst 

 making the gas; this absorbs the fumes, and will be 

 found strongly acid. The name of oxygen is, in fact, 

 derived from two Greek words "oxus," acid, and 

 "gennao," to produce; the early chemists imagining 

 that it was the sole acid-producer. The acids we refer 

 to as produced above, are the phosphoric and sulphurous. 

 A distinction is made between acids produced by 

 combinations of oxygen, and those produced by other 

 substances. Sulphuric, nitric, and many other acids, 

 depend for their qualities on the union of oxygen gas 

 with other substances. The hydrochloric and other 

 acids, however, have no oxygen in their composition ; 

 and hence it is proved, that oxygen is not the only 

 lament on which the production of acids depends. Its 

 importance, in this respect, is of the highest kind. 

 Of this, however, we shall have to speak more fully 

 hereafter. 



Oxides, as we have frequently mentioned, are combina- 

 tions of oxygen with- a metallic substance, by which 

 both alkalies and earths are also produced. These dis- 

 tinctions, which have existed from the earliest days of 

 chemical science, have a great convenience, as they 

 classify the oxides according to their special characters. 

 Thus, if oxide of iron, potass, soda, baryta, magnesia, 

 lime, Arc., were spoken of simply as oxides, their special 

 characteristics and qualities would not be so evidently 

 point. -.1 out Nevertheless, it is a rare case to find the 

 earths in a state of absolute freedom from those sub- 

 stances to which the term is most usually applied ; for, 

 as in the case of clay, lime, &e., oxide of iron is gene- 

 rally present; ami,' indod, the only source of all our 

 metal* in from rucks and sands, to which the term 

 "earths" is usually applied instead of tint f oxides. 



There are aim numerous instances in which an oxide 

 may, by an increase of oxygen, be converted into a sub- 

 stance having acid properties : or. perhaps, we may put 

 the question in another form, and state, that some sub- 

 will combine in such pro|M>rtins with oxygen as 

 ** ml*, p. KM ; Kl. 10. 



to form both oxides and acids. The following may 

 be selected as instances of these combinations : Iron 

 forms oxides, and also an acid the ferric when com- 

 bined with variable proportion* of oxygen : the same 

 occurs with the metals arsenic, chromium, A-c. 1 

 with chlorine an acid is formed by oxygen ; hence the 

 chloric and perchloric acids. But into these, and similar 

 combinations, we shall have to make an extended ex- 

 amination. 



Confining our attention to the production of ordinary 

 metallic oxides, wo may observe, that a vast variety is 

 found in their appearance and general characteristics. 

 Some metals, such as gold, silver, and platina, have 

 very little attraction for oxygen ; hence they may be 

 exposed to atmospheric and aqueous influence, and yet 

 remain unchanged for centuries. On the other hand, 

 the metals potassium, sodium, Arc., have so powerful 

 affinity for it, as to abstract it from almost any of 

 its compounds ; as may be seen by the following ex- 

 periment. 



Experiment 14. Throw a small piece of potassium on 

 to some water. The liquid will be rapidly decomposed ; 

 and so violent will be the action, that a Lirge amount 

 of light and heat is liberated. The result is the pro- 

 duction of potass, the alkali, or oxide of potassium, 

 which will be dissolved in the witter. 



Between potassium and gold, the affinities of the 

 metals for oxygen have a very extensive gradation ; 

 and yet such is modified by circumstances. Thus, not 

 only are air and moisture favourable to the production 

 of oxide ; but heat and electricity have a very powerful 

 effect, although that of the second force is generally 

 subsidiary to, or derived from, that of heat. Hence, 

 the process of oxidation is either slow or rapid, according 

 to the circumstances in which the oxidising body is 

 placed. The following experiments will fully illustrate 

 this fact. 



Jb's/xftment 15. Hang a piece of polished and thin 

 watch-spring in a jar containing some strong sulphuric 

 acid. The metal must not touch the acid, and the vessel 

 must be tightly corked. The polish will remain on the 

 metal for almost an) 1 length of time, because the acid, 

 by absorbing the moisture of the air in the vessel, 

 prevents the formation of an oxide on its surface. 



Experiment 16. Expose the same piece of spring to 

 air and moisture by placing it in a damp place. In the 

 course of a day or two, its surface will become covered 

 with oxide, owing to the oxidising action of air and 

 moisture together. 



Ejrjteriment 17. Heat a piece of polished iron or steel 

 in the flame of a spirit-lamp. Its surface will become 

 rapidly covered with rich colours, owing to the forma- 

 tion of various oxides. 



Efptriment 18. To one end of a piece of steel spring, 

 or twisted steel wire, as thin as possible, Fig. ts. 

 and about ten inches long, tie tightly 

 a piece of wick about an inch long, taken 

 from the inside of a composite candle or 

 a common taper. Pass the other end of 

 the spring through a bung or cork, which 

 will form a holder. On lighting the 

 taper and dipping it into a jar of oxygen, 

 the steel will catch fire, burning most 

 brilliantly, and filling the interior of the 

 jar with a red powder. Now here we 

 nave the rapid production of the oxide, which is caused 

 by the influence of heat in promoting the chemical 

 action of the pure gas on the metal. But the rapidity 

 of this is exceeded in that which takes place when a 

 powerful charge from a Leyden jar is sent through a fine 

 steel or brass wire. By that means the metal is in- 

 ttantaneously converted into an oxide. 



The reader will notice, by the last few experiments, 

 how much chemical action is modified by extraneous 

 circumstances. In fact, we have a double object in 

 introducing these experiments here. One being to show 

 the modifications which chemical action sustains in 

 respect to oxidation ; and the other, to introduce to the 

 notice of the student, the necessity which always exists 



