Lesson V.] 



CHEMISTRY. 



109 



in other positions than one above the other, but that their position does not alter the 

 materials. It is not absolutely imperative that pewter (an alloy of tin with lead and 

 antimony) should be made into measures, the same materials will form dish-covers, 

 hot-water plates, dishes, &c. ; and so it is with the atoms of certain materials, 

 as they are placed in groups, differing from each other in arrangement, so will the 

 compounds they form differ in their qualities, properties, and appearance. Some bodies 

 consist of the same elements, in the same ratio, and yet differ in their equivalents. 



QUESTIONS. 



50. T. What is the derivation and 

 meaning of the word isomeric ? 



P. It is derived from two Greek words, 

 isos (TOJ), equal ; and meros (/utpos), part ; 

 and is applied to those substances which 

 contain the same elements, in the same 

 proportions, and yet differ essentially in 

 their chemical qualities. 



51. T. How does the atomic theory 

 solve the problem of the isomeric state of 

 bodies depending upon the grouping of 

 their atoms ? 



P. Simply by demonstrating the ar- 

 rangement of the atoms. If we take twelve 

 square pieces of wood we can easily see how 

 this is effected. For example, we see that 



/!,. 2. 



tig. 10. 



in Fig. 9 the atoms are arranged in groups 

 containing six in each; in Fig. 10 each 

 group conta. 1 1 each group con- 



sists of two; and, i * atomscom- 



bine in groups of three. [See Question 47.] 



/. You said (Q. 41) that atoms have 

 weight How do you know that they have ? 

 P. Although we cannot weigh them, 

 because they are so small, yet it is certain 

 that they mutt possess some degree of 

 weight. If we take the common puff-ball 

 fungus in our hands, we are sensible that 

 it possesses weight ; when it bursts, and 



, its fine dust, we discover that each 

 particle is about y^irnjth of an inch in 

 diameter. Now it would be as absurd to 

 attempt to define the weight of one of 

 these particles, as it would be to weigh the 

 \ grain of musk, 



.if these i not possess 



weight, the puff-ball, or the grain of musk, 

 could not have weight. 



53. T. Have the atomic weights, or, as 

 they are sometimes called, the chemical 

 equivalents of the elementary bodies, been 

 determined ? 



P. Yes ; and arranged into groups. 



54. T. How are the elementary bodies 

 arranged ? 



P. They are divided into the non- 

 metallic and metallic groups. The non- 

 metallic elements are divided into gazolytct, 

 or bodies which are permanently gaseous ; 

 halogens, or bodies which produce salts 

 when combined with the metals; and 

 metalloids, or bodies resembling metals in 

 their chemical relations. 



55. T. How are the elements expressed 

 in chemistry ? 



P. By symbols, which were selected by 

 Derzelius, from Latin names, because that 

 language is known to all civilized nations. 



56. T. What is the use of symbols ? 



P. They enable us to express the 

 composition of a definite chemical com- 

 pound in a concise manner, by using the 

 initials of the elementary bodies, and 

 numbers annexed to them, denoting the 

 number of atoms of the several constituents 

 existing in the compound. 



57. T. Suppose that a symbol has not 

 any number allixc-d what does it mean? 



P. That only one atom of the substance 

 exists in the compound. 



58. r. Is there any particular n. 



of arrangement observed in expressing 

 chemical formula* by symbols f 



/._Yi-s. i substances, 



such as metals and salifiable bases, j : 

 electro-negative substances, such as oxygen 

 and acids, in th.- ' 

 frequently expressed by a dot, placed over 



odj ui-h which ; 



cnmb'in >*, oxide of lead is 



silica, si ; and sulphuric 

 we therefore learn that the lead 

 c 3 



