104 



CHEMISTRY. 



[Lesson III. 



P. Because a substance chooses or 

 elects one substance from several others in 

 preference, and to the exclusion of the rest, 

 and then combines with it. The particles 

 of a certain body, having an affinity for the 

 particles of another body, will unite with 

 them, but if they have not any affinity for 

 another body they will not combine. 



23. T. Give me an illustration of this. 



1\ [Experiment 6.] Here is a small 

 piece of gold, which 1 will place in this 

 wine-glass, and then pour some aquafortis 

 (nitric acid) upon it. [Does so.] You ob- 

 serve that no change has taken place ; but 

 when the gold is removed and some potash 

 added, chemical combination is the result, 

 and nitrate of potash, or saltpetre, is formed. 

 In this experiment we see that the acid had 

 a stronger affinity for the potash than the 

 gold, in fact, its affinity for gold is im- 

 perceptible. 



21. T. Then you think that some sub- 

 stances have a stronger affinity for one 

 substance than for another ? 



P. Undoubtedly; and if you refer to 

 the following tables you will see that it 

 really is the case. 



I. Sulphuric Acid. II. Oxygen. 



Baryta. 



Strontin. 



Potash. 



Soda. 



Lime. 



Magnesia. 



Ammonia. 



Zinc. 

 Lead. 

 Copper. 



Mercury. 

 Silver. 



Now, if we look at Table I. we see that 

 sulphuric acid has an affinity for ammonia, 

 and the result is sulphate of ammonia ; but 

 then, if we add magnesia to the solution, 

 decomposition will take place, and sulphate 

 of magnesia will be the result. This proves 

 that the acid has an affinity for all the 

 substances placed below the lime, and will 

 combine separately with each, but that the 



bases of the salts formed may be decomposed 

 or separated from the acid by adding any 

 of the substances above it to the solution, 

 until we arrive at baryta, and then we 

 find that the other substances do not exert 

 any power over the affinity of baryta and 

 sulphuric acid. The same thing occurs in 

 Table II. with regard to oxygen, and the 

 various metals placed underneath it. 



25. T. Are there any laws by which 

 the phenomena of chemical attraction a:o 

 regulated ? 



P. Certainly. 1st. The force is said to 

 e exerted in different degrees by various 

 bodies. 2nd. As it operates on the mole- 

 cules of bodies, it is found that its action 

 is promoted by any method which assists 

 the mechanical division and intermixture 

 of the minute particles. 3rd. Chemical 

 combination is generally attended by altera- 

 tion of temperature, and sometimes emission 

 of light. 4th. Opposite states of electricity 

 are observed between bodies which have an 

 affinity for each other. 5th. Chemical 

 combination consists of the combination 

 of a certain number of the molecules or 

 atoms of one body, with some definite 

 number of atoms of the other body com- 

 bining with it. 6. Chemical attraction 

 takes place either by simple or compound 

 affinity. 7. All compound bodies uniting 

 with other bodies without undergoing 

 decomposition, act as simple bodies. 



GENERAL QUESTIONS ON LESSON II. 



1. Is it necessary to have expensive 

 apparatus for the study of chemistry I 



2. Define chemical affinity. 



3. How many kinds of alkalies are 

 there ? 



4. Does chemical affinity change the 

 form and quality of bodies ? 



5. Is the force of chemical attraction 

 the same for all bodies ? 



6. What are the laws regulating chemical 

 attraction. 



LESSON III. 



WE do not require to study Chemistry very deeply to discover that an alteration of 

 temperature generally takes place when bodies combine. Heat is evolved when sulphuric 

 acid (oil of vitriol) is mixed with water, or when lime is slacked. The production of 

 cold takes place only when heat is rendered insensible by the conversion of a solid into 



