466 



FORMULA, CHEMICAL 



of engineering jobs upon railways, or in the country. The height is 2 foot 6 inches ; 

 tho length is 2 feet 9 inches ; the width 2 feet ; weight about 2 cwts. 



Holtzapffol describes another 

 ^ v portable forge of his own con- 



struction, possessing many ad- 

 vantages. 



With tho manipulations of 

 the forge, it is not the province 

 of this work to deal. 



FORK, a mining term. A 

 mine is said to bo ' in fork,' or 

 an engine to have the ' water in 

 fork,' when all the water is 

 drawn out. 



FORMATES. Compounds 

 with formic acid. See Watts's 

 1 Dictionary of Chemistry.' 



FORMATION. When em- 

 ployed in a geological sense it 

 signifies a group of rocks, referred 

 to a common origin, or belonging 

 to the same period. 



FORMIC ACID. (Acide 

 formique, Fr. ; Ameisensdurc, 

 Ger.) The acid which exists in 

 the bodies of ants, associated 

 with malic acid. 



Formic acid was obtained artificially, originally by Fisher of Leeds in 1670, and 

 (subsequently by Dr. Hulse, by distilling red ants. 



It may be prepared by boiling 1 part of starch with 4 of sulphuric acid, and 4 of 

 water, allowing the liquor to cool, and adding gradually 4 parts of the black oxide 

 of manganese, and distilling. For the reactions which take place, see Watts's ' Dictionary 

 of Chemistry.' Its formula is C 2 H0 3 ,HO (CH 2 O 2 ). It is a clear colourless fluid, which 

 crystallises below 32 Fahr., into brilliant plates. 



FORMUXJE, CHEMICAL The term formula, in ordinary chemical language, 

 is always understood to mean the collection of symbols indicating a compound 

 substance. Thus, if we allude to the letter or letters indicating an element, we say its 

 symbol ; but if we are speaking of a compoiind, we say its formula. It appears that 

 some short notice of the principles upon which the construction of chemical formuhe 

 depends is necessary to enable those who are not familiar with chemical language to 

 understand the few formulae employed in these volumes. For a complete account 

 of the philosophy involved in the construction, consult ' Watts's Dictionary of Che- 

 mistry.' The symbols of all the elements will be found under the head ' ATOMIC 

 WEIGHTS.' In constructing formulae there are several rules to be observed, the 

 neglect of which will lead to misapprehension of tho meaning intended to be con- 

 veyed. Substances in the most intimate union are expressed by placing the symbols 

 in juxtaposition. Thus oxide of lead is represented by PbO, dry sulphuric acid 

 (sulphuric anhydride) by SO 3 , acetic acid by C 4 H 4 4 . But where a compound is to 

 be expressed which is itself formed by the union of two compounds of tho class first 

 mentioned, such as an acid and a base, a comma is placed between them ; thus, 

 sulphate of lead is PbO.SO 3 , nitrate of copper CuO.NO 5 . The number of atoms, 

 when more than one enters into a compound, is expressed by writing the number on 

 the upper part of the right hand of the element. But if only one atom is to be ox- 

 pressed, the mere symbol is written. Thus oxide of copper is CuO, but the sub- 

 oxide is Cu 2 0. If preferred, the number multiplying the atom may be written at the 

 lower right-hand corner of the symbol ; Cu a O, and Cu 2 are identical in meaning. 

 If it be intended to multiply a formula not containing a comma or any other .sii:n, 

 such as SO 3 ; C 4 H 4 4 , &c., the number is to bo written on the left hand of the 

 formula, and is to be made larger than would be the case if it merely multiplied the 

 atoms of an element. Thus two atoms of oxide of lead are written 2PbO ; tlin-n 

 atoms of acetic acid, 3C 4 H 4 0*. But it is to be remembered that a number placed 

 on the left hand of a symbol or formula only multiplies as far as the first comma or 

 sign, so that if we wish to multiply a formula containing a comma or other sign, tho 

 formula must be placed between parentheses. Thus two atoms of sulphate of lead 

 are written 2(PbO,S0 8 ). If it be intended to express tho fact that one substance is 

 to be added to another, with a view to the production of a given compound or reaction, 

 the substances to bo added together are connected by a plus sign. For example, 



