ORGANIC ANALYSIS. When a complex organic substance is submitted to chemical oxamination the first point is to determine its proximate constituents, or, in other words, the several definite compounds of which it is made up. Opium, for example, is thus found to have as its proximate constituents meconic acrd, morphia, codeia, and acme 10 or 12 other substances. The modes by which these proximate constituents are separated are various; the chief being the action of certain solvents, such as ether, alcohol, and water, which extract some of the materials and leave others undissolved. Thus ether is the special solvent of fatty and waxy matters, resins, and camphors; alcohol dissolves the same substances with less facility, but on the other hand takes up many substances. which are insoluble in ether; while water, which scarcely acts upon the above-named matters, dissolves saccharine, gummy, and starchy matters, and salts of organic acids. The proximate constitutents being thus determined, the next point is to determine their qualitative and quantitative (or ultimate) composition; and it is to these processes—espe cially the last—that the term organic analysis is for the most part restricted.
Qualitative is shown in the article OltGANIC COMPOUNDS, that the ordi nary ingredients for which we must seek are carbon, hydrogen, oxygen, nitrogen, and sulphur. Carbon and hydrogen may be simultaneously detected by burning the com pound (which must be previously well dried) in a glass tube in contact with oxide of copper, which readily yields up its oxygen. The carbon is thus converted into carbonic acid, which, if passed into baryta water, forms a white precipitate of carbonate of baryta, and the hydrogen into water, which collects in drops in a small cooled receiver attached to the tube. Carbon may also be usually recognized by the black residue which almost always remains ou burning an organic matter, especially in a narrow test-tube in which there is little air. The presence of nitrogen may in most cases be readily ascertained by heating a portion of the substance in a test-tube with an excess of hydrate of potash, when a distinct odor of ammonia is perceived. Sulphur is detected by igniting the com pound with hydrate of potash and niter, whereby sulphuric acid is formed; and phos phorus and arsenic may be detected by the same means. The presence of oxygen cannot,
as a general rule, be directly determined.
Quantitative first attempts to determine the quantitative composition of organic bodies were made, more than half a century ago, by Gay Lussuc and Theuard. The process originally proposed by them has been modified and improved by various chemists, especially by llerzelius, Prout, and Liebig, and it is mainly owing to the great simplifications introduced by the last-named chemist, and to the consequently increased facility of conducting an ultimate analysis, that our knowledge of the compo sition of organic bodies has so vastly enlarged during the last 20 years.
The operation is always effected by causing complete combustion of a known weight of the body to be analyzed, in such a manner that the carbonic acid and water which are formed in the process shall be collected, and their quantities determined, from which, of course, the carbon and hydrogen they respectively contain may be readily calculated. The apparatus required for the analysis of a compound containing carbon, hydro gen, and oxygen only, consists of (1) a combustion tube, composed of hard white Bohemian glass, having a diameter of half an inch or less, and a length of from 14 to 18 incites. One end is drawn out in a point and closed, while the edges of the other (or open) end are made smooth by fusion in the blow-pipe flame. (2.) A thin sheet iron furnace, in which the tube is placed and supported during combus tion. (3.) A small light tube (which may be either a bulb-tube, as in the figure, or a U-tube, which is filled with fragments of spongy chloride of calcium to absorb the watery vapor that is driven through it; and (4) Lie big's bulb-apparatus, containing a solu tion of potash of specific g,r.wity 1.27, for the purpose of absorbing the carbonic acid. The ehloride-of-calcium tube is connected by a well-dried perforated cork to the open extremity of the combustion tube, and by a little tube of flexible caoutchouc, secured by silk cord, to the potash apparatus.