OKOAXIC ANALYSIS.] 



CHEMISTRY. 



409 



the bodies under examination, because we can almost 

 always obtain vegetable products in a condition verging 

 on absolute purity. Of course, if an analysis were re- 

 quired for commercial purposes we must be very exact 

 in that respect also. Philosophically, we may consider 

 flour, for instance, to be a compound of gluten and starch, 

 and the analysis of it, and the detection of the elements 

 present, would be restrained within the limits we have 

 named. If, however, we have to conduct the analysis 

 for agricultural purposes, we should pay far greater heed 

 to what we have termed the " accidentals," such as 

 silicious matter, phosphate of lime, <fec. , because the 

 presence of such substances in the soU whence the wheat 

 is produced is essential to its growth. If, therefore, we 

 desired to analyse the wheat as a guide to the manage- 

 ment of the soil, with respect to manure, etc., this matter 

 then becomes of the highest importance. We shall, how- 

 ever, leave such till we enter upon the department of agri- 

 cultural chemistry, to which they properly belong. Similar 

 remarks are applicable to other technical applications of 

 organic analysis. 



We have already stated that the carbon, hydrogen, and 

 oxygen existing in a vegetable product, are all resolvable 

 into carbonic acid and water by the process of combustion, 

 and the fact points out the course which must be 

 adopted in conducting an analytical investigation. Many 

 methods, both of a special and general nature, have been 

 proposed ; but the following is an outline of the plan 

 visually adopted at the present time, and for which we 

 are chiefly indebted to Dr. Liebig : 



(a). The substance to be analysed must, if solid, be 

 reduced to as fine a powder as possible ; this is best 

 effected in a glszed Berlin porcelain mortar. After being 

 powdered sufficiently fine, it may then be introduced into 

 a tube, and exposed to a heat short of boiling water, if 

 it will bear that without decomposition, which almost 

 every substance will safely do. 



(l-j. It has then to be mixed with a considerable quan- 

 tity of the black oxide of copper. This substance af- 

 fords oxygen to any combustible mixed with it, when 

 the two are exposed to a red heat. This is effected by 

 introducing both in to a German glass tube about eighteen 

 inches long and an inch in diameter, which must have 

 one end drawn out to a fine point. The substance to be 

 analysed is to be mired with the oxide whilst the latter 

 is in a warm state, so as to prevent any danger of tin- 

 absorption of moisture. A little clean oxide is first in- 

 troduced into the tube, then the mixture of the substance 

 and oxide ; and some more oxide is then added, which, 

 of course, will be at the open end of the tube The 

 following cut represents the tube as filled, a being the 

 fine end, which is closed, b b the portion filled with 

 Fig. 77. 



i 



the mixture, and c that part containing the copper turn- 

 ings. When filled, the tube is to be laid horizontally, 

 and gently tapped, by means of which the mixture will 

 be spread evenly throughout the length. About three 

 grains of the substance which, of course, must be ac- 

 curately weighed is to be mixed with abomt an ounce to 

 an ounce and a-half of the oxide. 



(c). This tube is then placed in a peculiar shaped fur- 

 nace, go that the combustion may proceed in a gradual 

 manner, commencing from the wide end of the tube, till 

 it is completed at the narrow end, which is to be last 

 heated. The wide end, however, projects beyond the 

 furnace, for reasons we shall presently mention. The 

 furnace is made of wrought iron plate, and should be 

 about a foot long, and four inches wide and deep. At 

 about two inches distance throughout its length, holes 

 half an inch wide, and two inches long, are to be cut 



VOL. L 



a, a, a, a, a, a, as in the following figure, which re- 

 presents the furnace, with the lower part uppermost 



Fig. 78. 



(Fig. 78). Between each of these holes a small iron 

 upright is placed (see 6 in Fig. 78), on which the tube is 

 to rest during the process of combustion. 



The fuel used is charcoal, which is first introduced in 

 small quantities, at o, and gradually added, so as to 

 Fig. 79. 



carry on the combustion from o to c (Fig. 79). By 

 these means a complete combination of the elements 

 contained in the substance in the tube is effected, with 

 the oxygen of the oxide of copper. 



(d). At the end d, in the figure above, a tube is to be 

 attached by means of an india-rubber connexion. This 

 tube is to contain fused chloride of calcium, for the 

 purpose of receiving the aqueous vapour generated 

 during the combustion. By this, the amount of water 

 produced is readily ascertained ; and so the hydrogen 

 and oxygen of the mixture are weighed away. A useful 

 form of tube for this purpose is represented in the fol- 

 lowing cut (Fig. 80), in which is shown that part which 

 is attached, by india rubber connexions, to the combus- 

 tion tube, placed in the furnace ; and 6, that end attached 

 to the potass apparatus, to be described immediately. 



Fig. 80. 



(). The next piece of apparatus which is attached to 

 the tube, shown above at 6, is the potass bulb, repre- 

 sented in the annexed cut. The ob- j^g. 91 

 iect of this is the absorption of car- 

 bonic acid, by means of pure liquid 

 caustic potass, with which it is 

 nearly filled ; and by means of which 

 the carbonic acid, produced during 

 the combustion, becomes removed, 

 and affords us the opportunity of 

 ascertaining the amount of carbon 

 in the body under examination. 

 This potass bulb is attached, air-tight, 

 to the end of the chloride of calcium 

 tube, and so forms the end of the whole arrangement. 



It will be perceived that we have only hitherto referred 

 to the analyses of those substances containing carbon, 

 hydrogen, and oxygen ; and having described the different 

 apparatus used, we subjoin a cut representing the whole 

 in operation. 



Fig. 83. 



, .. - , 



i a a. the combustion tube ; b t, furnace resting on two bricks : c, con- 

 nection of the combustion tube with the chloride of calcium tube, d ; e, 

 the connection between the chloride of calcium tube and, /, the potau 

 Apparatus ; g, the open end of ditto. 



The following particulars must be carefully attended 



3o 



