Lesson III.] 



CHEMISTRY. 



105 



a fluid, or a liquid into a gas. [Experiment 7.] Thus, by combining three parts of 

 sulphate of soda, and two parts of diluted nitric acid, eighty degrees of cold is produced. 

 [Experiment 8.] If we mix two parts of pounded ice with one part of chloride sodium 

 (common salt), we shall cause the mercury in a thermometer to sink to five degrees, 

 when surrounded by the mixture. This effect will always be produced, whatever may 

 be the temperature the thermometer was occupying previous to the experiment ; the 

 mercury will never fall lower. 



Before entering into the consideration of other matters, it will be necessary to examine 

 some of the phenomena attending combustion : Firstly. Because they are intimately 

 connected with heat ; Secondly. Because they are so frequently witnessed, and so little 

 understood by the chemical student. 



QUESTIONS. 



26. 7*. What is COMBUSTION ? 



P. The phenomena exhibited by burn- 

 ing substances, which are attended by heat 

 lit, and the production of new com- 

 pounds. 



T. Will any substance burn ? 



It must be a combustible 

 substance. 



26. 7*. Suppose that we heat a piece of 

 iron, and make it what is commonly termed 

 red- hot, is not that combustion ? 



although it emits light and 

 heat it does not burn, it is only incandetcent 

 or ignited. 



/'. Then what do you mean by 

 combustion ? Give me an example. 



/'. The body experimented upon burns 

 or consumes in combustion ; but, when 

 rendered incandescent, it cools again, and 

 remains unaltered, or nearly so. For ex- 

 ample, [Experiment 9] take a piece of 

 charcoal and set it on fire ; it will I. urn 

 and waste away, and finally leave a residue 

 of white ash. \V. know that it has been 

 consumed by combustion, and heat has 

 been evolved ; we feel the heat, and there- 

 fore know such is the case. When we heat 

 a bar of iron, heat is evolved, l.ut the iron 

 does not consume, because its temperature 

 is not kept up by the heat evolved in its 

 union with the oxygen of the air. 



/ How in it that the charcoal is 

 ycd, and the iron is not f 

 P. The charcoal is not deitroyrd, but 

 altered in ' . < is not any such 



i* destruction in Nature. Matter 

 .ilthottgh its form 

 tor annihilation is contrary to the 

 laws of Nature. 



31. T. How do you know that substances 

 are altered in form, without being de- 

 stroyed ? 



P. By experiment [Eperiment 10.] 

 If I place a piece of heated charcoal under 

 a glass jar it generates a gas called carbonic 

 acid, which is known by adding some lime- 

 water, the result of which is a white pre- 

 cipitate of carbonate of lime. 



32. r. Do the substances which burn 

 support combustion ? 



P. No, they neither support it, nor 

 burn, unless when assisted by a supporter 

 of combustion, which will not burn of 

 itself, although it supports combustion. 



33. r. What is the chief supporter of 

 combustion .' 



P. Oxygen gas. 



34. r. How do you know that it sup- 

 ports combustion ? 



/'.Ik-cause, if a lighted candle is 

 plunged into this gas, the taper burns more 

 brilliantly, but the gas itself is not i 

 If the same candle is plunged into ajar of 

 coal gas the gas is ignited, and the candle 

 extinguished. 



/'. Is it not possible to burn iron, 

 and other bodies of a like nature ? 



/'.Yes ; we can burn the most in- 

 combustible bodies by means of the oxjr- 

 :i blowj.ijif, even tobacco-pipes, 

 pipe-clay, * v . 



hen I placed a lighted 

 under a glass jar, the jar became covered 

 with moisture, and then tin- caudle went 

 out. NVh.tt was the rcn- 



F.1 he moisture was water, caused by 

 the hydrogen of the candle uniting with 



