108 



CHEMISTRY. 



[Lesson V. 



crystallizes in octahedral crystals, will be 

 amorphous from a (a ) without, and morphe 

 (uopcfnj) form, or devoid of regular forms. 

 For example, I have eight balls here, and 

 can arrange them into many forms, thus : 

 abed e 



OOO O OO O 

 OOO OOO OO OO 



00 



OOO OO OO 



OO 



oooo 



OO 



O 



OO OOO 



but it is possible to make them assume 

 more figures than those I have formed, and 

 as it is probable that all the atoms of 

 bodies are not the same size, we can easily 

 understand how the form of bodies is altered 

 by the arrangement of their atoms. 



48. T. Explain how this affects their 

 form. 



P. I have four apples here, 1, 2, 3, 4 ; 

 and if I place them upon the table, as in 

 fig. 7, and draw four lines round them, I 



Fig. 7. 



shall have a figure like that represented by 

 a, b, c, d, in Fig. 8, which has its four sides 

 equal. Suppose that I remove the apple 

 marked 2 from within the square, and place 

 a nut in the spot marked 5 in Fig. 7, and 

 then draw a line (In) so as to touch the 

 apples 1 and 4, and include the nut, the 

 form will be similar to the shaded part 

 within the square. If we substitute two 



large cricket-balls for the apples 1 and 2, 

 the figure will be wedge-shaped, like that 

 within the lines i c, c d, d k, and k i ; but, 

 if we put the balls where 2 and 3 are, the 

 figure will be similar to that enclosed by 

 the lines ah, hg, gd, df, ft; and eo. 

 Let us suppose that the apple marked 2 is 

 removed, and replaced by a pear; provided 

 it is the same size, the form will not bo 

 altered. It is thus with the atoms of some 

 crystals, they may be removed, and replaced 

 by other atoms, without altering the form 

 of the crystals ; hence we infer that certain 

 atoms are isomorphous. 



49. T. What do you mean by the term 

 isomorphous ? 



P. The term is derived from two Greek 

 words, isos (icros) equal, and morphe (/iiop^) 

 form, and signifies of the same form. For 

 example, the phosphate and biphosphate of 

 soda are of the same form as the arseniate 

 and binarseniute of soda, and only differ in 

 the one salt containing phosphorus, and 

 the other arsenic. 



GENERAL QUESTIONS ON LESSON IV. 



1. What is the difference between a 

 mixture and a combination ? 



2. How are chemical combinations 

 classified ? 



3. Explain the atomic theory. 



4. Have all bodies atoms resembling 

 each other ? 



5. Can we weigh atoms ? 



6. To what purpose has the knowledge 

 of the relative weights of the atoms of bodies 

 been applied ? 



7. Explain the terms amorphous and 

 isomorphous. 



8. How does the arrangement of atoms 

 influence the form of bodies ? 



LESSON V. 



THERE are some facts connected with the atomic theory which are worthy of remark. 

 We observe that certain substances, having different forms and qualities, are composed 

 of the same materials. How is this to be accounted for 2 The atomic theory comes to 

 our assistance, and seems to say that it is the arrangement of the particles or atoms. 

 For example, the cyanic and fulminic acids are isomeric compounds of carbon, oxygen, 

 and nitrogen. From this we learn that the same elements may be grouped in different 

 ways, which is the same as saying that having a dozen bricks it is possible to place them 



