12 DECREPITATION 



Neutral bodies are frequently, however, so constituted, that the neutrality does not 

 arise from the circumstance of an acid being saturated with a base, but from the 

 energies of two elements being, to some extent, satisfied by the fact of their being in 

 combination. Thus, water is a neutral substance, nevertheless it may be decomposed 

 by a variety of processes, several of which are susceptible of quantitative precision. 

 In the first place, it may be decomposed by passing steam over a metal capable of 

 uniting with its oxygen with liberation of the hydrogen. It may also be electrolysed, 

 and the two gases separately obtained. 



Organic or inorganic neutral salts may, at times, be very completely and simply 

 decomposed by means of the battery. Not only are the various processes in electro- 

 metallurgy founded on this principle, but it has even been practically applied to the 

 quantitative estimation of the metals in ores. The electrolysis of the neutral salts of 

 the great series of organic acids of the general formula C n H"0 4 has thrown great 

 light on some previously obscure points in the radical theory. 



The decompositions undergone by organic substances in contact with reagents arc 

 so manifold, that the limits of this work preclude the possibility of doing more than 

 glancing at a few of the most general and interesting. Perhaps of all the modes of 

 inducing the breaking up of more complex into simpler substances, the application of 

 heat is the most remarkable for its power and the varied and opposite character of 

 the substances produced. It has been shown that, as a decomposing agent, heat 

 possesses no special function. From complex organic molecules all classes of sub- 

 stances are formed. Individual substances belonging to every chemical type are, 

 therefore, found among products of destructive distillation. Acids, alkalis, and 

 neutral bodies of every kind are formed, and some of the most interesting and beauti- 

 ful bodies known to chemists are found in the uninviting-looking tar of coal. Let 

 us illustrate this by a glance at a few of the coal-tar products. Among the acids are 

 the oxyphenic, carbolic, and cresylic. The alkaloids represented are methylamine, 

 ethylamine, propylamine, butylamine, amylamine, pyridine, picoline, lutidino, colli- 

 dine, parvoline, chinoline, lepidine, cryptidine and aniline. Among hydrocarbons, 

 benzole, toluole, xylole, cumole, cymole, propyle, butyle, amyle, caproyle, caproylene, 

 oenanthylene, naphthaline, anthracene, chrysene, pyrene, acetylene, &c. This list, 

 probably, does not include one half of the substances produced from coal by the de- 

 composing and recomposing influence of heat. 



Mineral acids exercise a powerful decomposing influence on organic substances. Of 

 these the nitric and sulphuric are the most commonly used. Nitric acid is especially 

 active, owing to its twofold action. By virtue of its oxidising tendencies, it breaks up 

 great numbers of substances into more simple and less carburetted derivatives, and the 

 hyponitric acid produced by the removal of one of the atoms of the oxygen of the 

 acid frequently enters into the resulting compound, a substitution-product being the 

 final result. In the latter bodies produced in this manner the hyponitric acid (NO 4 ) 

 generally replaces hydrogen, the original type remaining unaltered. The production of 

 oxalic acid from sugar; succinic, lipic, adipic, pimelic, suberic, &c., acids from oily 

 and fatty matters by the action of nitric acid, are examples of its oxidising power ; 

 while the formation of nitrobenzole, and bodies of more or less analogous character, 

 present instances of the replacement of hydrogen by hyponitric acid. 



Sulphuric acid owes its decomposing power to its extreme tendency to combine 

 with water. Many of the less stable organic bodies are, by this means, absolutely 

 broken up, so that the resulting products are of a character too indefinite to allow of 

 the changes being expressed by an equation which shall render a true account of all 

 the substances directly or indirectly formed. On the other hand, the action may !>< 

 so controlled by the careful regulation of the temperature and strength of the acid 

 that products may be eliminated which are themselves totally broken up and destroyed 

 Ly an acid of greater strength. The production of grape-sugar by the action of sul- 

 phuric acid on starch, or lignine, may be taken as an example. It not unfrequently 

 happens, that the sulphuric acid unites with the substance acted on to form ;i conju- 

 gated compound. Benzole, and many other hydrocarbons, as well as oxidised bodies, 

 behave in this manner with concentrated sulphuric acid. 



Chlorine and the other halogens are powerful decomposing agents, acting chiefly 

 by virtue of their affinity for hydrogen. The principal effects produced by them are 

 oxidation and substitution. The oxidising action of the halogens arises from the 

 decomposition of water ; the hydrogen combining with the chlorine, &c., to form an 

 hydracid, and the free oxygen uniting with the other substances present. 



The above sketch will sufficiently indicate some of the most usual methods l.y 

 which the decomposition of organic and inorganic bodies is effected; but hundreds 

 of other decomposing agencies are at the call of the chemist, when any phenomena 

 involving the disruptions of compounds are to bo investigated. C. G. W. 



DECREPITATION (Eng. and Fr. ; Vcrknistcrn, Ger.) is the crackling noise, 



