S Y M 



S YM 



1. Each symbol represents one equiva- 

 lent of the elementary substance : thus H 

 denotes one equivalent of hydrogen. A 

 figure prefixed multiplies the symbol: 

 thus 2H, 3H, 4H, denote tviro, three, 

 and four equivalents, respectively. Two 

 equivalents are sometimes denoted by 

 placing a dash through, or under, the 

 symbol : thus f J , or H, signifies the 

 same as 2 H, or two equivalents. 



2. Compounds are represented by 

 placing the symbols of their elements 

 together. Thus, S F e denotes sulphuret 

 of iron. Or the compound may be 

 expressed by an algebraic formula, as 

 S+Fe. 



3. A dot ( • ) prefixed to, or placed over, 

 a symbol, indicates one equivalent of 

 oxygen. Thus 'H or H denotes one equi- 

 valent of oxygen and one of hydrogen, 

 or H -H O. Each additional dot denotes 

 another equivalent : thus, :C, or C, de- 

 notes one equivalent of carbon and two 



of oxygen, or carbonic acid ; : • N, or N, 

 denotes one of nitrogen and five of ox- 

 ygen, or nitric acid. 



4. A figure prefixed to any symbols 

 multiplies all the following symbols 

 which are not separated from it by a -f 

 sign. Thus 2-H :S = 2 •H-l-2 : S; 

 in this case, the compounds 'H and • S 

 are both multiplied by 2. But in the fol- 

 lowing formula, 



2 H : S -I- -K = 2 -H + 2 : S -H K, 

 the two first compounds only are multi- 

 plied by 2, the third being merely added. 



5. A figure placed after any symbol 

 multiplies that symbol, but does not eflfect 

 any other symbol in the formula. Thus, 

 H2 C = 2 H + C ; in this case, H is mul- 

 tiplied, while C is only added. In the 

 formula, N H^ = N + 3 H, the latter 

 symbol alone is multiplied. 



6. In complicated combinations, brackets 

 are often used to contain the symbols 

 which are supposed to be united. Thus, 

 in the formula 



[2HC2N + C2NFe] + 2 -K, 

 there are two compounds ; the former is 

 composed of the symbols within the 

 brackets, the latter consists of the sym- 

 bols placed outside the brackets. 



7. A figure prefixed to any number of 

 symbols enclosed within brackets, multi- 

 plies them all, whether there are inter- 

 vening signs or not. A figure prefixed 

 to the symbols within the brackets in the 

 preceding paragraph, multiplies them all, 

 but does not effect the symbol outside 

 the brackets. 

 325 



8. The animal and vegetable acids 

 were expressed by Berzelius by the first 

 letter of their names, with a dash over 

 it : thus T, A, C, are the symbols for tar- 

 taric, acetic, and citric acids. By others, 

 they are represented by Italic capitals, 

 some succeeding letter being added when 

 more than one acid have the same initial 

 letter : thus T, A, Ct, represent the acids 

 above mentioned. 



9. A few exercises on symbols are here 

 added. To the left of the sign ( = ) are 

 placed the materials used ; to the right, 

 the products formed by their reaction. 

 The symbol * & ' is used to signify a sub- 

 stance added to, or separated from, an- 

 other, while + is placed between sub- 

 stances chemically combined : 



Materials. Products. 



•H&Fe = Fe&H 

 •H&Fe& *:S = jS-Fe&H 



:Hg = Hg&02 

 2 :Mn = :Mn2&0 



5 •N2&P2 = ::P2&10N 

 4-N2& SFe = :S -Fe&SN 



::N = jN&O 

 2 : : N & : N = 3 . : N 



S & 02 = : S 

 HS & O3 = • H & : S 



^ -Phfe Z = ^ Z&Pb 

 :C-Pb&HS = -H&SPb&cC 

 SY'MMETRY (ffuju/xerpoc, commen- 

 surable). The etymological meaning of 

 this term, and the meaning with which 

 it was first employed, in mathematics, by 

 Euclid, is commensur ability : two mag- 

 ■itudes, then, were symmetrical which 

 admitted of a common measure ; hence, 

 the term was applied to magnitudes 

 which coincide. 



1. But Coincidence had been already 

 denoted by the terms equal and similar, 

 the former relating to size, the latter to 

 form. Symmetry, therefore, was even- 

 tually employed to express that obvious 

 relation of equal and similar figures, 

 which refers to t\ie'\x position merely, and 

 consists in their corresponding portions 

 being similarly placed on different sides 

 of the same straight line. In the letter 

 W there is a want of symmetry, but not 

 in O : to make W symmetrical, both the 

 inner lines should be thin, and both the 

 outer lines thick. 



2. In Algebra, z function is said to be 

 symmetrical with respect to any two 

 letters, when it would undergo no change 



