793 



CHEMICAL FORMULA. 



CHEMICAL FORMULAE. 



794 



A similar train of reasoning has recently been very ingeniously 

 applied by Williamson, Brodie, and Odling, to carbon, oxygen, sulphur, 

 and some other elements, the atomic weight of which ought, accordiug 

 to these chemists, to be doubled. In the case of carbon this might 

 probably be done with advantage ; but the doubling of the atomic 

 weight of oxygen, although it would allow certain classes of organic 

 compounds to be represented by somewhat more simple f ormulse, would 

 yet add considerably to the complexity of others. Although these 

 views have not yet been generally adopted, they have received the 

 assent of several of the most eminent chemists. For further details 

 on this subject see an excellent paper by Dr. Odling in the ' Quarterly 

 Journal of the Chemical Society,' vol. xi. p. 107. [ATOMIC THEORY.] 



CHEMICAL FORMULAE. The use of symbols in chemistry to repre- 

 sent elements has given rise to the use of groups of symbols to represent 

 groups of elements. Such groups of symbols are formulae. Formerly 

 the metals which were then known were represented by the zodiacal 

 signs of the sun and planets ; and shortly after the isolation of the 

 great bulk of the non-metallic elements, arbitrary symbols were in- 

 vented for their representation, and formulas were constructed by the 

 juxtaposition of these symbols. The clumsiness, for this purpose, of 

 the zodiacal signs, and of those subsequently proposed, has prevented 

 their use. The symbol adopted universally, at present, for an element 

 is the first letter of its Latin name, in those cases where it has been 

 named in the Latin tongue. If, as is the case with most elements, its 

 discovery is of later date, the first letter of the name given to it is 

 employed for its symbol. But, as there are about sixty elements, and 

 only twenty-six letters in the European alphabet, the names of some 

 elements must necessarily commence with the same letter. To obviate 

 the ambiguity which naturally results from this, the symbols of the 

 less important of the elements beginning with the same letter are com- 

 pounded of the initial letter and some other letter in their names. 

 The first (or only) letter is always written of the capital size, the 

 second is written small. 



In a few instances, different names are given to the same element by 

 the Germans, French, and English, and consequently different symbols 

 are used in the three countries. Thus, the French name for nitrogen 

 is azote, and its symbol in that country is Az. The metal which the 

 English call bismuth is called in Germany wismuth, and its symbol is 

 there Wi. The Germans call tungsten, wolfram ; and both they and 

 the English symbolise it by W, &c. Fortunately, however, these are 

 almost the only instances where such dissimilarity exists. 



In a few instances compound bodies have received special symbols, 

 aa well as those built up from the symbols for the elements of which 

 such compounds are formed. The following table shows all the 

 elements which are at present definitely known, with their symbols. 



Aluminium . 

 Antimony . 

 Arsenic . . 

 Barium . 

 BUmuth 

 Boron . 

 Bromine . 

 Cadmium . 

 Calcium 

 Carbon . 

 Chlorine 

 Chromium 

 Cobalt . 

 Copper . 

 Didymium < 

 Erbium . 

 Fluorine . 

 Glucinnm . 

 Gold 



Hydrogen 

 Iodine 

 Iridinm 

 Iron . 



Lanthanum 

 Lead 

 Lithium 

 Magnesium 

 Manganese 

 Mercury . 

 Molybdenum 

 Nickel 

 Niobium 



Al 

 Sb 

 Al 



Ba 



Bi 



Bo 



Br 



Cd 



Ca 



C 



Cl 



Cr 



Co 



Ca 



Dl 



Er 



Fl 



01 



Au 



H 



I 



If 



Fe 



La 



Pb 



Li 



MK 



Mn 

 Hg 

 Mo 

 Nl 

 No 



Nitrogen . 



Osmium . 



Oxygen 



Palladium 



Pelopium . 



Phosphorus 



Platinum 



Potassium 



Rhodium 



Ruthenum 



Selenium 



Silicon 



Silver . 



Sodium 



Strontium , 



Sulphur 



Tantalum 



Tellurium 



Terbium 



Tin . 



Titanium 



Thorium . 



Tungsten 



Uranium . 



Vanadium 



Yttrium . 



Zinc 



Zirconium 



Water . 



Oxalic acid 



Tartaric acid 



N 



Os 



O 



Pd 



PI 



P 



Pt 



K 



R 



Ru 



Se 



81 



Ag 



Na 



Sr 



s 



Ta 

 Te 

 Tr 

 Sn 

 Tl 

 Th 

 W 



u 



V 

 Y 

 Zn 

 Z 



One of these symbols, therefore, used alone, denotes an indefinite 

 amount of the element which it represents. But as a consequence of 

 the law of definite chemical combination, when more than one element 

 is present in a chemical compound a more precise meaning attaches 

 itself to such a symbol. It signifies, in such case, one atom or com- 

 bining proportion of the element. [See ATOMIC THEORY and CHEMICAL 

 EQUIVALENTS.] Thus CO denotes six parts of carbon combined with 

 r i^ht of oxygen, and is consequently the formula of carbonic oxide. 

 When more than one equivalent of an element is in chemical combi- 

 nation, the number of equivalents or atoms is attached above or below 

 to the symbol representing the element. So that C0 2 or CO S is the 

 formula for carbonic acid, which contains six parts of carbon to six- 

 teen of oxygen. 



A chemical formula of a compound body, which merely gives the 

 elements present and their total respective quantities, is said to be an 

 irrational or empirical formula. In many compound bodies, evidence, 

 either analytical or synthetical, points to the existence of a closer 

 union between certain elements or groups of elements than obtains 

 between others. A chemical formula which expresses this more or 

 less thoroughly is more or less a rational fwrnula. The purpose of 

 a rational formula, therefore, is to represent the structure of a com- 

 pound, or the grouping of the elements of which it is composed. 

 The most intimate union of two elements, or two groups of elements, 

 is expressed by the simple juxtaposition of their symbols or formulae 

 (KC1, chloride of potassium). In cases of less intimate union, a comma 

 is introduced (NH 4 Cl,PtCl 2 , bichloride of platinum ammonium). When 

 two elements or groups are still more loosely combined, they are con- 

 nected by the plus sign, + (CuOSO, + 5HO, penthydrated sulphate of 

 copper). When several molecules or groups of elements are concerned, 

 the number of such molecules is represented either by embracing the 

 group in brackets and attaching the number to the bracket, or by 

 placing the number before the group, in which latter case the number is 

 a factor of all the symbols after it as far as the next sign (, or + ) of less 

 intimate combination, Fe 3 3 (S0 3 ) 3 Persulphate of iron, or Fe 2 3 3S0 3 . 



An example will illustrate this. 



Aluminium combines with oxygen in the proportion of two atoms of 

 aluminium to three of oxygen, Al 2 3 (alumina). 



Sulphur combines with oxygen in the proportion of one atom of 

 sulphur to three of oxygen, S0 3 (anhydrous sulphuric acid). 



Alumina combines with anhydrous sulphuric acid in the proportion 

 of one molecule of alumina to three molecules of sulphuric acid, 

 A1 2 3 3S0 3 (sulphate of alumina). 



Again, potassium combines with oxygen in the proportion of one 

 atom of potassium to one of oxygen, KO (potash). 



Potash combines with anhydrous sulphuric acid in the proportion of 

 one molecule of potash to one molecule of sulphuric acid, KOS0 3 

 (sulphate of potash). 



Further, sulphate of alumina combines with sulphate of potash, hi 

 the presence of water, in the proportion of one molecule of the sul- 

 phate of alumina to one molecule of sulphate of potash, KOSO S , 

 AljO-jSSOj ; and finally, this latter compound salt combines with water 

 in the proportion of one molecule of the compound salt to twenty-four 

 molcules of water, KOS0 3 , Al 2 3 3S0 3 -p24HO (crystallised potash 

 alumina alum). The above is an instance of the representation by a 

 rational formula of the structure of a compound as derived from its 

 synthesis. The empirical formula of the same body would bo 

 KAl,S t H,/> <0 . 



Again, if we take borax and heat it, we find that a certain quantity 

 of water is given off. The residue remains so far unchanged that it 

 dissolves in and crystallises with water, giving rise to the original 

 substance. ( We conclude hence that 



Borax = 2 + uHO. 



2, on being treated with sulphuric acid, gives rise to sulphate of soda 

 NaOS0 3 , and another body, S v whence 



If the substance 2^ be heated with sodium, soda NaO is formed, and a 

 new body, 2j, appears as a black powder ; hence 



2j refuses to be further decomposed ; it is therefore an element, and is 

 called Boron. Consequently, borax consists of oxide of sodium and 

 oxide of boron. For the determination of the numbers n, m, and p in 

 the above equations, the reader is referred to the articles ATOMIC 

 THEORY and CHEMICAL EQUIVALENT. The rational formula for 

 borax is 



NaO BoO 3 HO Bo0 3 + 9HO. 



It must, however, be borne well in mind, that all rational formulas are 

 partial, inasmuch as they cannot express the whole of the molecular 

 arrangements of the bodies to which they refer ; and arbitrary, because 

 they cannot but give undue prominence to particular theoretical views 

 and tendencies. A compound body may be divided into different 

 proximate constituents, according to the different substances which act 

 upon it, and according to the different physical conditions which 

 accompany such action ; and one and the same body may be con- 

 structed synthetically from different groups of elements. Thus, alco- 

 hol, when heated to a certain temperature with strong sulphuric acid, 

 gives up water, being converted into ether. Hence it may be viewed 

 as the ethylate of water 



HO, C 4 H 5 0. 



But at a higher temperature sulphuric acid transforms alcohol into 

 olefiant gas, or ethylene, depriving it thereby of twice as much water 

 as it did in converting it into ether : whence alcohol may be viewed as 

 olefiant gas and water 



2HO, C 4 H 4 . 



Or, synthetically, alcohol may be formed either by acting upon chloride 

 of ethyl with hydrated potash, 



C 4 H 4 C1 + KO HO = C.H.OHO + KC1, 



