Lessor. 



CIIF.M1>TKY. 





atom of oxygen combine and form water, 



the atomic weight of which is 9 ; hence it 



follows that the relative weight of the atom 



of hydrogen to the at- n is as 



. which is the same as saying that 



>:n of hydrogen weighs one grain, 



and the atom of oxygen eight grains. 



38. T. Then I suppose that is the 

 reason water is always said to be composed 

 of 1 volume of hydrogen and 8 volumes ol 



/'. You are correct. It is nothing more 

 than saying, water is composed of * 

 measures of each gas, instead of volumes. 



39. T. Do not some bodies combine 

 in all proportions ? 



/'. Yes ; for example, gold and silver, 

 water and alcohol, and water and sulphuric 

 acid. Other bodies combine in all pro- 

 s to a certain point, but cannot be 

 made to combine after that ; for example, 

 water will dissolve and hold in solution any 

 salt, (as alum or Epsom salts,) but after it 

 has dissolved a certain portion, it is said 

 to be saturated, and cannot dissolve any 

 more. Some bodies unite in several defi- 

 oportions ; for example, 14 parts 

 of nitrogen will combine with 8*16, or 2-t 

 parts of oxygen, but will not combine with 

 any intermediate proportion. Certain bodies 

 unite in only one proportion, as chlorine 

 and hydrogen. 



40. 3". Have all bodies the same kind 

 of atoms ? 



/'. \c bodies have simple 



atoms, and compound bodies have com- 

 pound atoms. For example : 



HtniATK or 



SODA. 

 Ox rosy. Some*. 



rig. . 



/ ; and 4 are diagrams representing 

 simple atoms of oxygen and sodium 

 (natrium), but Fig. 5 represents the com- 

 1 atoms of nitrate of soda. 



Live these atoms any weight, 

 m say the atomic weight of water 

 1091 



' > not know anything of the 

 absolute weight of atoms; they arc too 

 mall to weigh ; therefore we c.n 

 determine the rvfctfev weight of atom*, but 

 it is certain that atoms have some weight. 



/.How can you determine the 

 relative atomic weight of bodies ? 



P. By fixing a particular number, as 

 the atomic weight ot" any one su: 

 and then determining the atomic weights 

 of other bodies, according to the propor- 

 tions by weight in which they uni 

 example, let us assume that the atomic 

 weight of hydrogen is equal to 1, the 

 atomic weights of other bodies may then 

 be found; thus 100 parts of sulphuretted 

 hydrogen contain 5-9 parts of hydrogen 

 and 9 1*1 parts of sulphur. We suppose 

 that there are an equal number of atoms 

 of hydrogen, and the same of sulphur, 

 therefore we have the proportion < 

 91-1 equal to 1 : 16. Thus we know that 

 the atomic weight of sulphur is 16, if that 

 of hydrogen iu 1. 



/'.Has the knowledge of the rela- 

 Jits of the atoms been usefully 



P. Yes ; the relative weights of the 

 atoms of bodies, and their chemical equiva- 

 lents, are expressed by the same m; 



. Who in vente tithe atomic theory ? 



/'. Dalton, in 1804. He supposed the 

 atoms of bodies to be spherical, and 

 invented symbols to represent the n 

 in which he thought they combined 

 together. Thus, hydrogen was represented 

 by a circle with a dot in the centre ; 

 nitrogen, by a circle with a vertical line 

 drawn through the centre ; oxygen, by a 

 plain circle; and carbon, by a black 



/'.How did he classify the combi- 



1'. Those substances containing only 

 2 atoms he called binary compounds, those 

 mmpounds, those 

 with 4 atoms, quaternary, &c. 



46. T. Is it probable that the disposi- 

 tion or arrangement of the atoms of solid 

 bodies can influence their form .' 



P. Certainly. When a solution of 



any salt is set aside to crystallize, and the 



process goes on slowly, rtgular crystals aro 



; l>ut it it is too sudden, the 



crystals are irregt; 



47. T. How docs this prove that form 

 depends upon the arrangement of the 

 atoms ? 



/'.If th.y are arranged suddenly ami 

 order, the same salt that always 



