814 



ORGANIC ANALYSIS. 



with other compounds being sufficient to vitiate 

 the conclusions deducible from our experi- 

 ments. Having ascertained the purity of our 

 substance, the next care is to ensure its com- 

 plete desiccation. For this purpose the fol- 

 lowing plan, recommended by Liebig, will be 

 found the most efficient (fig. 429). A small 

 quantity of the material to be dried is placed 

 in an inverted syphon-tube (c), the bend of 

 which is plunged into a vessel (D), contain- 

 ing water gradually heated to the boiling 

 point. When plain water is used, the tem- 

 perature of course will not rise above 212; 

 but by substituting for it different saline solu- 

 tions we may at pleasure obtain any degree of 

 heat between 212 and 300, according to the 

 nature of the compound to be analysed. A 

 current of dry air is made to pass over the 

 substance by connecting one limb of the sy- 

 phon with a tube containing chloride of calcium 

 (A), and the other with a vessel (E) closed at 

 top, excepting the aperture by which it is con- 

 nected with the syphon-tube, and rilled with 

 water, which is allowed to run out at the 

 bottom with a speed regulated by a stop-cock 

 (/'), the place of the liquid being supplied by 

 air, which has passed over the chloride of cal- 

 cium and then through the syphon-lube. Vo- 

 latile liquids that are unchanged by distillation 

 should be allowed to stand two or three days 

 upon fragments of fused chloride of calcium; 

 the liquid should then be decanted and dis- 

 tilled in a small retort; in other cases, as in 

 the examination of fats or fixed oils, it may be 

 more convenient to dry the material in a watch- 

 glass placed in an ordinary water-bath or the hot- 

 water oven previously described. The further 

 progress of the analysis will vary according to 

 the form and composition of the substance to 

 be examined. 



We shall describe the methods of analysing 



1. A solid, which does not contain nitrogen. 



2. A fluid, which does not contain nitrogen. 



3. A substance, which docs contain nitrogen. 



1. Analysis of a solid not containing nitrogen. 

 The combustible which answers best in these 

 experiments is charcoal ; it is the least expen- 

 sive, and very manageable, but dusty. Spirits 

 of wine or pyroxylic spirit, no doubt, are 

 cleaner, but their expense is a great objec- 

 tion. Gas has been tried by myself and others 



in a variety of ways, but though some modi- 

 fications of burner answer tolerably well, it is 

 not on the whole to be recommended. 



The best furnace to be used with the char- 

 coal is represented at A, Jig. 430, and is made 

 of stout sheet-iron bent into the form of a 

 trough, open at one end ; the plate which 

 closes the other is perforated with an aperture 

 three-quarters of an inch in diameter, to allow 

 the passage of the combustion tube ; the fur- 

 nace is about twenty inches long, five inches 

 at top, two inches and three-quarters at bottom, 

 and three inches high. Transverse slits are 

 made along the floor at intervals of two inches 

 for draught, and between each are rivetted vef- 

 tical stiff pieces of sheet-iron one inch high, 

 terminating in a concave edge above, for the 

 support of the combustion tube. The appa- 

 ratus may rest on bricks during the operation, 

 as represented in the wood-cut. 



The tube in which the mixture is burned, 

 the combustion or retort tube, (Jig. 430, a, b, c,) 

 should be of difficultly fusible glass free from 

 lead, about fifteen inches long and half an inch 

 in diameter: the hard Bohemian glass answers 

 the purpose perfectly. The tube may on cer- 

 tain occasions be drawn out into a fine but 

 strong tail bent upwards at an obtuse angle, 

 and the mouth should be smoothed by making 

 it red hot in the flame of the blowpipe, so 

 that a cork need not be torn in adjusting it. 



The apparatus for containing the chloride of 

 calcium which collects the water, or drying 

 tube, is conveniently made of the shape de- 

 picted (Jig. 430, B): it consists of a tube 

 about half an inch in diameter and four inches 

 long. Upon one end is blown a bulb, to contain 

 a larger portion of the chloride, and from the 

 bulb a strong tube of small diameter extends 

 for an inch and a half. The chloride of cal- 

 cium with which it is filled must not be fused, 

 but should be prepared merely by evaporating 

 the solution of the chloride to dryness by a 

 strong sand heat. A porous mass is thus ob- 

 tained, which does not crystallize by absorbing- 

 moisture, as the fused variety does, to the de- 

 struction of the tube that contains it. In order 

 to charge the apparatus a few fibres of cotton 

 wool are put into the bulb, and by sucking air 

 through the small end adjusted over the aper- 

 ture of the fine tube to prevent any minute 

 particles from falling out : into the apparatus to 



Fig- 430. 



Liebit/'s apparatus for the combustion of organic bodies. 



A, sheet iron trough or furnace containing the retort tube a, b, c, and resting on 

 the bricks E E. 



B, the dryiug tube charged with chloride of calcium, or pumice stone moistened 

 with sulphuric acid. 



e, the potash bulbs ; d, caoutchouc connector. 



D, the suction tube, shewing the mode of its adjustment when used for draw- 

 ing air through the apparatus at the termination of the experiment. 



