processes. I am anxious, therefore, to impress upon the student the necessity of bestowing equal attention and diligence upon both; the rules which I have laid down are the fruits of long experience and of innumerable experiments.

A. ANALYSIS OF COMPOUNDS WHICH CONSIST SIMPLY OF CARBON AND HYDROGEN, OR OF CARRON, HYDROGEN, AND OXYGEN.

§ 140.

The principle of the method which serves to effect the quantitative analysis of these compounds, and which owes its present perfection to Professor LIEBIG, is exceedingly simple. The substance under examination is burned into carbonic acid and water; these products are separated from one another, weighed, and the carbon of the analyzed substance calculated from the weight of the carbonic acid, the hydrogen from that of the water. If the sum of the calculated weight of the carbon and hydrogen is equal to the original weight of the substance, the absence of oxygen is at once satisfactorily proved; should the sum on the other hand be less than the original weight of the substance, the difference will at once indicate the amount of oxygen originally present in the analyzed compound.

The combustion is effected either by igniting the organic substances in conjunction with oxygenized bodies which readily yield up their oxygen, (oxide of copper, chromate of lead, &c. &c.,) or directly, by means of free oxygen gas, or, finally, at the expense both of free and combined oxygen.

a. SOLID BODIES.*

a. Readily combustible, non-volatile substances. (Ex. gr. sugar, starch, tartaric acid, in short, most solid organic substances.)

* For the analysis of waxy, fatty and other similar bodies, which cannot be reduced to powder, I refer to § 145.

$141.

I. APPARATUS AND PREPARATIONS NECESSARY FOR ORGANIC

ELEMENTARY ANALYSIS.

The following is a complete list of every thing required for the performance of organic elementary analysis:

1. THE SUBSTANCE INTENDED FOR ANALYSIS.-This must be very finely levigated, and perfectly pure and dry;-for the method of effecting the exsiccation of organic substances, I refer to § 14.

2. A TUBE IN WHICH TO Weigh the subSTANCE.-A small and perfectly dry glass tube, about 1 to 2 inches long, and a few lines in diameter, is selected for this purpose; the weight of this tube is to be accurately determined. It is advisable to place the tube in the drying apparatus together with the substance intended for analysis.

3. THE COMBUSTION TUBE.-A tube of difficultly fusible glass, (potass glass,) about one half line in thickness, three feet in length, and from 0.4 to 0.5 inches in diameter, is softened in the middle before a glassblower's lamp, drawn out as represented in

PLATE XLVI.

and finally rent asunder at a. The fine points of the two pieces are then slightly thickened in the flame, and the sharp edges of the open ends slightly rounded by fusion, care being taken to leave the aperture perfectly round; it is necessary for this purpose to select in the first place a tube, of which the apertures represent the appearances illustrated by Plate XLVII, but not that exhibited in Plate XLVIII.

PLATE XLVII.

PLATE XLVIII.

CC 2

Two perfect combustion tubes are thus produced. The combustion tube intended for use, is cleaned with a linen or paperwiper attached to a piece of wire, and is subsequently thoroughly dried. This is effected either by placing the tube, with a piece of paper twisted over its mouth, upon the plate of a common stove, or into a sand-bath, and keeping it there for some time; or, in cases where it is desirable to accomplish the exsiccation in a more expeditious manner, by thrusting a small glass tube into the combustion tube, heating the latter in its whole length, by moving it backwards and forwards over the flame of a spirit-lamp, and continually removing the hot air by suction.

PLATE XLIX.

The tube, when perfectly dry, is closed air-tight with a cork, and kept in a warm place until required for use.

4. A LIEBIG'S APPARATUS, as illustrated by

PLATE L.

PLATE LI.

and which may be readily procured from any maker of chemical instruments, or from any glass-blower. This apparatus is filled to the extent indicated in the engraving, with a clear solution of caustic potass of 1.27 sp. gr., and which must be free from admixture of carbonate of potass, (§ 40. 7.) The introduction of the potass solution into the apparatus, is effected by plunging the extremity a (but never the other) into the vessel which contains the potass ley, and applying suction to the other extremity (b,) either by means of perforated cork, or, better still, with

the aid of a syphon, (Plate LI.) The two extremities are then wiped perfectly dry with twisted paper slips, and the apparatus is finally wiped dry with a clean cloth.

5. THE CHLORIDE OF CALCIUM TUBE (Plate LII.) may also be purchased. This tube is prepared for use in the following manner :

PLATE LII.

In the first place, the end a of the tube b a is loosely stopped with a cotton plug, which is made to protrude

from to inch into ba;

this is effected by introducing a very loose cotton plug into c, and applying a sudden and energetic suction to b. The bulb of the tube is then filled with small lumps of chloride of calcium, (§ 40. 8. b.), and the tube dc is filled up to e with smaller fragments, intermixed with coarse powder of the same substance; a loose cotton plug is placed over the chloride of calcium, and the tube is finally closed with a perforated cork, into which a small glass tube is fitted; the protruding part of the cork is cut off, and the cut surface covered over with sealing-wax; the edge of the little tube f g is slightly rounded at g by fusion, (vide Plate LIII.)

PLATE LIII.

6. A SMALL CAOUTCHOUC TUBE. This is made in the following manner : a piece of sheet india - rubber is slightly warmed by gentle stretching, and subsequently bent round a moistened glass rod; the superfluous portion is removed, with sharp and perfectly clean scissors, at one cut, when the fresh cut edges of the caoutchouc, pressed closely together, will completely cohere, provided they have not been soiled by contact with the fingers.-Another piece of india rubber is then stretched round the first piece, and cut in the same manner, taking care to place the cut edges of the inner and outer tube on opposite sides

This kind of double cautchouc tube will stand the wear and tear of fifty and more analyses. It is carefully drawn off the glass rod, and dried at a very gentle heat, (the temperature of the waterbath is far too high for this purpose.) The diameter of this little connecting tube must be sufficiently wide to permit the ready introduction of the extremity a of the potass apparatus, and of the tube f g of the chloride of calcium tube. (Plate LIII.)

7. SILK CORD.-A strong twisted silk cord is selected; this is cut into pieces of from two to ten inches long, and each of them tied into a knot at both ends.

8. CORK STOPPERS. Soft and smooth corks, as much as possible free from visible pores, are best adapted for this purpose; a cork should be selected which fits perfectly tight, and enters into the mouth of the combustion tube only onethird of its length; a perfectly smooth and round hole, of the same diameter with the end ba of the chloride of calcium tube, is then patiently and carefully bored through the axis of the cork by means of a fine round file; into this perforation the end ba of the chloride of calcium tube must fit perfectly airtight. The cork, thus prepared, is finally dried in the waterbath. It is necessary always to have two corks of this description ready.

9. A MORTAR.-A porcelain mortar, of greater width than depth, should be selected; it must be provided with a lip, and free from indentations and fissures, and should not be glazed inside. The mortar is washed with water previously to use, and kept in a warm place, until required.

10. A SUCTION TUBE.-Plate LIV. illustrates the most appropriate form of a suction tube.

PLATE LIV.

The aperture a is closed with a perforated cork, into which the tube b of the potass apparatus is fitted.