1--3 



OUOANIC ANALYSIS. 



ORGANIC ANALYSIS. 



101 



The treatment of the several liquid extracts obtained as above 

 described u the next point for conitidrratitiu ; but here the field of 

 experiment becomes so greatly enlarged that anything like a detailed 

 description of it would 'lead us far beyond the limit* of the present 

 article. Suffice it to say, that fractional distillation, fractional crystal- 

 lisation, and fractional precipitation form the bases of operation 

 adopted in the separation and isolation of organic proximate prin- 

 



The examination of the residue after an organic material has been 

 successively subjected to the action of the above liquids, U not a 

 rnittur of very great difficulty, inaxiuuoh as it can only consist of such 

 substances aa hgnin and cellulose. Nor U it difficult to extract one 

 proximate principle only from organic material, experience of the 

 properties of similar principles here guiding to the most proper 

 method. 



The physical and chemical properties that should characterise an 

 organic proximate' principle have already been alluded to at the com- 

 mencement of this article ; it now, therefore, only remains to consider 



I'ltimate Organic Analysis. 



From what has been stated, it is evident that this operation mainly 

 consists in the determination of the quantities of carbon, hydrogen, 

 oxygen, and nitrogen contained in any organic substance. Chlorine, 

 bromine, iodine, sulphur, and phosphorus are comparatively very rarely 

 met with ; they ore estimated in the manner described under each of 

 those elements, or by some slight modification of the methods there 

 given. 



The first point to be attended to in an organic analysis, or com- 

 bustion, as it is practically termed, is the removal of hygroscopic 

 water the removal of that moisture which most bodies absorb by mere 

 contact with the atmosphere. This may be done in several ways ; a 

 very good one consists in placing the body over a surface of oil of 

 OM. triol under the receiver of an air-pump and 



f. exhausting, when complete desiccation speedily 

 I takes place. This process has the advantage of 

 not requiring the application of heat, sometimes a 

 I ^^psssism ij point of great importance. Substances that bear 

 . I ^ff a temperature of 212 Fahr. are dried either in 

 ^^* a water oven, or are placed in a curved tube of 

 the annexed form, which is introduced into boiling water and dry air 

 drawn through it. Sometimes mere exposure to dried air at common 

 temperatures is sufficient to desiccate a substance. 



The next step in the process is the accurate weighing of the material. 

 For this purpose the latter is usually inclosed in a small tube, and a 

 balance employed that will indicate jj^th of a grain. 



The following are the principles involved in the actual analysis : 

 First, of compounds containing carbon, oxygen, and hydrogen ; for 

 nitrogen must be estimated by a separate operation. It is well known 

 that when coal or wood, or anything containing the three elements 

 alluded to, is burned, the carbon takes up oxygen from the air and 

 Ttsnnm off under the form of carbonic acid, while the hydrogen com- 

 bines with the quantity of oxygen requisite to form water and passes 

 off as steam. Further, it is also well known that these combinations 

 take place in fixed and unvarying proportions ; that six parts of carbon 

 always combine with sixteen of oxygen to form carbonic acid ; and 

 that one part of hydrogen always combines with eight parts of oxygen 

 to form water. On these facts, then, is founded the process about to 

 be described; for, obviously, if a weighed quantity of the wood, coal, &c., 

 were taken, and the whole of the carbonic acid and water formed could 

 be collected and weighed, we should be in possession of all the data 

 required for finding the amounts of carbon, hydrogen, and oxygen 

 originally present. The total amount of carbonic acid divided by 22 

 and then multiplied by 6, would give the quantity of carbon ; the 

 total amount of water divided by 9 would show the quantity of hydro- 

 gen ; and the difference between the combined weights of the carbon 

 and hydrogen, and the weight of the original substance, would give the 

 quantity of oxygen. 



The burning of the substance must be perfect ; there must be no 

 production of compounds intermediate between the original substance 

 on the one hand, and the carbonic acid and water on the other. 

 That the oxygen of the air is insufficient for this purpose is i-vi.l.-nt. 

 when we remember that smoke is nearly always produced under 

 such circumstances, and smoke is partly composed of those inter- 

 mediate bodice, the production of which it is indispensable to avoid. 

 The desired burning agent must, then, be one that will so readily yield 

 its oxygen to organic matter at an elevated temperature, as to ensure 

 complete oxidation of the substance to carbonic acid and water ; at 

 the same time it must be itself unalterable by the high heat employed. 

 These apparently somewhat antagonistic properties are possessed by 

 the black anhydrous oxide of copper. [COPPER.] About four or five 

 grains of the powdered and dried substance ore introduced into a tube 

 (a, Jig. 1) made of very infusible glass, about 15 to 20 inches long, 

 nearly half an inch in diameter, drawn out to a point at one end 

 (6, fg. 1), and previously about one-third filled up with oxide of 

 copper that has been dried by igniting to rednen and allowing to cool 

 in a well-closed, long, narrow bottle : a little more oxide of 'copper is 

 then |x.ured in, and the substance well mixed with the oxide by means 

 of a wire twisted at one end into a corkscrew shape ; more oxide i 



again introduced, the wire passed once or twice through it to wash off 

 adhering substance, and the tube finally filled up with oxide to within 

 two inches of its open extremity. On heating this tube and its con- 

 tents to redness, first near its open end (c.jig. I), and then gradually 

 throughout its whole length, the organic matter U thoroughly burnt 

 into carbonic acid and water, the manner of separating and collecting 

 which will presently be described. 



With regard to the best material for heating the tube, much must 

 depend upon circumstances. Till within the lost few years charcoal 

 has been the fuel almost always employed, some pieces of which ore 

 made red-hot in a furnace, and then placed, a few at a time, first round 

 the anterior part of the tube (c, Jig. 1 ), the latter being supported on 

 sheet-iron crosspieces in the sheet-iron trough, dd, represented in the 

 accompanying drawing. 



Fig. 1. 

 / 



The combustion of charcoal, however, occasions a troublesome 

 amount of dust, and, since the introduction of gas into laboratories, 

 many furnaces have been contrived by means of which the glass tubes 

 may be gradually and regularly heated with that fuel. The latest 

 improvement in this respect is by Dr. Hofmann, the general arrange- 

 ment of whose furnace is seen in Jig. 2. 



Fig. 2. 



In this apparatus the combustion of the gas is effected by means of a 

 number of perforated clay burners, so grouped as to form a channel 

 for the combustion tube, a system of stop-cocks permitting to confine 

 the heat to any special place in which it may be required at the time. 



The arrangement by which the water and carbonic acid, formed during 

 the operation from the organic substance, are collected, is very simple. 

 A small gloss tube, straight, as seen at c, ./?</. J , or bent to the shape of 

 the letter U, and having a bulb attached, as seen at c, Jig. 2, is filled 

 with pieces of fused chloride of calcium, and firmly fixed by a cork, 

 or solid india-rubber plug, into the glass combustion tube. Imme- 

 diately at the opposite extremity of the chloride of calcium tube a 

 piece of apparatus, known as 'Liebig's potash bulbs' (/, fy. 1), is 

 attached by a piece of india-rubber tubing (g). The vapour of water 

 and carbonic acid evolved from the tube are thus thoroughly absorbed, 

 the former by the chloride of calcium, and the latter by a strong 

 solution of caustic potash previously placed in the bulbs. The whole 

 length of the tube having been brought to a red heat, and there main- 

 tained till no more bubbles of gas pass into the potash, the charcoal is 

 removed from the extremity, the little point It broken off, and air 

 cautiouslv drawn through the whole arrangement by aspiration, with 

 a piece of india-rubber tubing attached to the potash bulbs. In this 

 last operation loss may be occasioned by the air carrying a little vapour 

 of water away from the potash solution, and hence the use of the little 

 tube h, which contains a short stick of solid hydrate of potash. In 

 place of driving out the residual vapour of water and carbonic acid by 

 air, a few fragments of chlorate of potash may be placed in the 

 posterior extremity of the tube ; and on heating this at the close of 

 the operation, evolution of oxygen takes place, and effects the desired 

 object. The use of chlorate of potash here is attended with two 

 or three advantages, but it in liable to be decomposed so rapidly 

 as to blow some of the solution of potash altogether out of the 

 bulbs. Another and greater modification of the process consists in 

 having a considerable elongation of the tube in the place of the 

 little capillary extremity above described : into this open end a little 

 platinum or porcelain boat, containing the organic substance to be 

 analysed, can be placed, and a stream of pure and dry air or oxygen 

 passed over it. On then gradually heating the gloss tube in the neigh- 

 bourhood of the boat, the substance burns as it would do in air ; but 

 the products of combustion pass on over the ignited oxide of copper, 

 and are collected respectively in the chloride of calcium tube and 

 potash bulbs. At the same time any inorganic, non-volatile matter 



