CHEMISTRY. 



[OKQAXIC ANALYSIS. 



of newly-developed principles. TlieM have been 

 M> numerous M to defy cnuioent u. In tli art ol 

 dyeing, for fmtMw^ the discovery and use of aniline 

 hu completed an eutiru resolution in tho processes em- 

 ', ployed ; and gu-Ur, which previously wai employed 

 almost solely for the preMrratiun of timber, U now the 

 3uroe of thooe beautiful colour*, mauve. Magenta, <to., 

 which afford -u. h rieli tint* to cotton and silken fabric*. 

 :ill first give a general account of such sub- 

 stance*, A-c., which being directly or mediately produced 

 from planta, have for their chief component parts, tho 

 elements of hydrogen, oxygen, and carbon, or any two 

 of these. Baring thus, as it were, given the elemen- 

 tary principle* of this department of chemical science, 

 we shall proceed to examine other and more complex 

 I. . - 



With scarcely an exception, vegetable bodies consist 

 entirely of carbon and water, or the elements of water 

 united with carbon in various proportions. To fami- 

 liarise the mind of the student with the products of 

 vegetable substances resulting from chemical action, we 

 shall here give the formula) of water, carbonic acid, and 

 other compounds, in which these or their elements are 

 involved. We shall use their symbols, to save space in 

 imiiiftting their composition. 



Water . 



Carbonic acid 

 Alcohol . 

 . 



Acetic acid 

 Oxalic acid 

 Tartaric acid 

 Sugar 

 Starch 



HO 

 CO. 



c 4 



, o, 



C. H, O, 



L'l 'i -f. O - i 

 C. H, 10 



O 



Now, on inspecting the above list, we find that a 

 union of the same elements, in various proportions, is 

 capable of producing unbalances having entirely different 

 I'p'l-crties. Thus, alcohol, ether, acetic acid, tartaric 

 acid, and sugar, each contain precisely the same ele- 

 ments, but in different proportions ; and yet there is 

 not the least apparent similarity in their specific pro- 

 perties. These facts just point out the extensive variety 

 of forms and substances which carbon, oxygen, and 

 hydrogen can produce by their union, and the learner may 

 thus have some idea of the wide range of that interest- 

 ing field of investigation into which we are now 

 entering. 



We shall here point out two singular and instructive 

 facts connected with the composition of four of the 

 substances to which we have called attention namely, 

 sugar, alcohol, ether, and acetic acid. In producing 

 alcohol from sugar, as in the ordinary process of fer- 

 mentation, we find that carbonic acid is largely pro- 

 duced, which passes off in a gaseous form. This accounts 

 for the difference of composition between the sugar and 

 alcohol. In producing ether from alcohol, we lose no 

 carbonic acid, but only an equivalent of water ; so that 

 alcohol may be regarded as composed of ether -j- water. 

 Acetic acid (which is the cause of the acid flavour of 

 ordinary vinegar) is readily produced from alcohol, and 

 in that process we lose three equivalents of hydrogen 

 and gain one of oxygen, by the oxidising effect of the 

 atmospheric air employed ; so that acetic acid may be 

 regarded as a compound of four equivalents of carbon 

 1 with three of water. We can thus produce from 

 sug.ir, so far as we have gone, three different bodies 

 having exactly the same elements in various propor- 

 tion*, each different, and yet chemically analogous. 



Referring now for a moment to oxalic acid, we find 

 that really consists of a union of carbonic oxide (CO) 

 with carbonic acid (CO,), for the two would afford two 

 equivalents of carbon and three of oxygen, which is 

 precisely the constitution of oxalic acid in an anhydrous 

 state. But if we speak of ordinary oxalic acid, we shall 

 find that it is combined with three equivalents of 

 wator (3HO), which would make the combination as 

 follows : 



C. + O, + 3DO ; or, C, + O. + H.. 



And in this formula we see how oxalic acid may be 

 in. > In. -I-.1 from starch or sugar (the usual source). 

 Now, if we add concentrated sulphuric acid to oxalic 

 acid, having tho latter formula, decomposition ensues, 

 its water U removed, and an equivalent, each of carbonic 

 oxide and acid, is afforded. 



As we proceed, we shall have to extend the number of 

 elements in our formuho, and include nitrogen. \Yo 

 shall, however, for the sake of simplicity, defer our 

 remarks on this point till we have more fully described 

 tho simpler kinds of organic compounds. 



The existence of carbon in vegetable bodies is con- 

 stantly L-vidouccd to our senses in the process of burn- 

 ing. Thus, in baking, toasting, roasting, and burning 

 any vegetable body, a black mass is produced, which is 

 owing to the carbon forming part of it being set free, as 

 charcoal. In any of these processes, the hydrogen and 

 part of the oxygen escape as water. The remaining 

 portion of the oxygen combines with a portion of the 

 carbon, and passes away as carbonic acid. Even the 

 solid charcoal left, will gradually be converted into car- 

 bonic acid by combining with the atmospheric oxygen 

 which surrounds it. The following formula shows the 

 results of an entire combustion of a portion of absolute 

 alcohol, which we shall take as a type of such results 

 obtained during the combustion of other substances. 



Results of the Combustion of an Equivalent of Alcohol 

 Alcohol. 



C4 



lid 



= 24 

 = 8 



= 16 



4COj = M 

 QUO - S4 



O i a from the at 



n re, to 

 support com- 

 bu&uou . 



14] 143 



We thus perceive, that by the combustion of one 

 equivalent of alcohol with twelve' of oxygen gained from 

 the atmosphere, the oxidation of the spirit should 

 produce four equivalents of carbonic acid ami six of 

 water. 



In the early pages of this section, we have had frequent 

 occasion to remark on the beautiful simplicity, and the 

 value of the doctrine of chemical equivalents. But as 

 we proceed in our investigation, we shall still further 

 admire the sagacity of its discoverer. It is impossible 

 to spoak too highly of its use in this department of ex- 

 perimental science ; in fact, organic chemistry has 

 developed the nature of atomic values beyond the most 

 sanguine expectations of the great Dalton. 



The remarks and illustrations we have made, are, of 

 xmrse, only intended as introductory to our subject. 

 We shall next speak of organic analysis, because it lays 

 at the foundation of our investigations ; and without its 

 exercise it would be impossible to proceed a step in re- 

 lating the natural history of the various substances we 

 shall have to examine. 



ORGANIC ANALYSIS. 



tw our previous pages* we gave extended directions for 

 ,he qualitative and quantitative analysis of inorganic 

 xidius. The principles and. details we then explained, 

 whilst incident to the analysis of organic bodies, are so, 

 lowever, only to a limited extent, because our range over 

 the nature of the elements with which we have to deal is 

 also limited. In inorganic analysis we may happen to find 

 any of about sixty different elements, and an almost inter- 

 minable number of their compounds. In organic analysis 

 we chiefly wish to detect the proportions of carbon, hydro- 

 gen, and oxygen present, and occasionally have to expect 

 litrogen. We do not trouble ourselves so much in re- 

 r erence to what we may call accidental substances, which 

 are not absolutely essential to the typical constitution of 

 * See unit, pp. 394407, locliuir*. 



