ORGANIC ANALYSIS. 



817 



capillary neck of the bulbs inverted into the 

 liquid; the bulbs are then warmed by the flame 

 of a spirit-lamp, so that on cooling they shall 

 be about three-fourths filled with the liquid. 

 The necks are now sealed by the blowpipe- 

 flame, and the bulbs again weighed ; the in- 

 crease of weight gives the quantity of the 

 liquid which has entered, and which is to be 

 analysed. The oxide of copper having been 

 heated, and allowed to cool with the usual pre- 

 cautions, about an inch and a half of the retort 

 is filled with pure oxide ; we then take one of 

 the bulbs, draw a file across the capillary neck, 

 put the bulb into the tube, break off the neck 

 by pressure against the glass, and drop the 

 broken portion in with the bulb; we then pour 

 in a couple of inches of oxide of copper, 

 introduce the second bulb in the same manner 

 as the first, and till up the tube with oxide, 

 cork it and strike it smartly on the table as 

 before to secure free air-way. The combustion- 

 tube is now connected with the exhausting 

 syringe, but no heat applied; on gently working 

 the syrine, the air and vapour in the bulbs 

 will expand and drive out the liquid, which 

 will be quickly absorbed by the oxide of 

 copper around ; we adjust the apparatus in the 

 furnace as before, and gradually heat the upper 

 half of the tube; when this is red, we vola- 

 tilize the fluid by cautiously approximating a 

 piece of ignited charcoal, taking especial care 

 not to heat the tube too much ; by degrees all 

 the liquid in the first bulb is expelled, and we 

 proceed in like manner with the other; the 

 whole tube is finally heated carefully, and the 

 after part of the process conducted in the 

 manner already described. 



If the liquid be not volatile, an oily acid 

 for example, a small vessel is made by taking a 

 piece of glass tube about a quarter of an inch in 

 diameter, sealing one end, and while hot press- 

 ing it on a flat surface, so as to make a firm 

 basis on which it may stand upright; it should 

 be cut off the tube so that the little vessel be 

 about an inch high. It is weighed at first 

 empty, and a second time with the liquid for 

 analysis ; an inch or two of oxide of copper is 

 put into the combustion-tube, then the vessel 

 with the liquid. On inclining the tube suffi- 

 ciently, the liquid runs out and is made to 

 diffuse itself over the inner surface of the lower 

 half of the tube, which is to be filled with oxide 

 of copper, and the analysis to be cautiously 

 proceeded with in the usual way. 



Substances which contain a great excess of 

 carbon sometimes escape complete combustion 

 by this process; when this is feared, all danger 

 may be averted either by adopting the plan of 

 Dumas, already mentioned, or by pulverizing 

 some chlorate of potash finely, which is care- 

 fully dried, mixed with about four times its 

 weight of oxide of copper, and the first portion 

 of the retort is filled with it for about an inch ; 

 the tail-like prolongation may in this case be 

 dispensed with at the close of the operation ; 

 instead of sucking air through the apparatus, 

 we very cautiously apply heat to the chlorate, 

 oxygen is evolved, which burns the last traces of 

 carbon and displaces the gas and aqueous vapour 



VOL. III. 



which the tubes contain. When the chlorate 

 has been used, the last inch of oxide of copper 

 must be kept separate from the rest, as it will 

 be mingled with chloride of potassium, and 

 must not be employed again until it has been 

 washed from the salt, for as chloride of copper 

 is slightly volatile it would be deposited in the 

 drying tube and unduly increase its weight. 

 If the heat is too suddenly applied, a portion 

 of the chlorate is apt to be carried forward me- 

 chanically, and this constitutes the chief ob- 

 jection to its use. 



Sometimes chroinate of lead is advantage- 

 ously substituted for oxide of copper with sub- 

 stances difficult of combustion, as by a bright 

 red heat alone it gives off a portion of its oxy- 

 gen. It is easily prepared by precipitating the 

 chromate or bichromate of potash with solution 

 of acetate of lead. It should be well washed 

 and heated to incipient fusion before it is used 

 for analysis. It has the advantage of being 

 much less hygroscopic than the oxide of cop- 

 per. To ensure accuracy, when much gas (as 

 in this case, and in instances where nitrogen is 

 present,) passes through the potash apparatus 

 during the whole experiment, it is best to con- 

 nect the open extremity with an additional 

 drying tube, charged with solid hydrate of 

 potash instead of chloride of calcium, the 

 weight of which has been carefully noted, as 

 a portion, very small but still susceptible, of 

 aqueous vapour is carried off from the solution 

 of potash by the gas, and would otherwise be 

 lost, making the quantity of carbon appear 

 somewhat too little. 



3. Analysis of a body containing nitrogen. 

 Two separate analyses are in this case re- 

 quired ; the first, to discover the proportion of 

 carbon and hydrogen; and the second expressly 

 for the nitrogen. When bodies containing 

 nitrogen are burned with oxide of copper, a 

 variable proportion of the lower oxides of 

 nitrogen is formed, which being retained by 

 the chloride of calcium or potash would render 

 the analyses incorrect. A precaution is there- 

 fore employed which renders it necessaiy to 

 make use of a retort-tube somewhat longer 

 than common ; it is charged as usual to within 

 four inches of the opening, and then filled up 

 with clean copper turnings ; the apparatus is 

 arranged as before directed, the copper turnings 

 are brought to full redness, and the analysis 

 proceeded with cautiously in the ordinary man- 

 ner. As the oxides of nitrogen pass slowly over 

 the ignited copper they are decomposed, the 

 oxygen combining with the copper while pure 

 nitrogen escapes ; the quantity of carbon and 

 hydrogen is determined exactly as heretofore. 



To ascertain the proportion of nitrogen, the 

 most accurate method is that recently devised 

 by Vanentrapp and Will, and suggested about 

 the same time by Berzelius ; the fundamental 

 fact consists in the observation of Gay Lussac, 

 that when azotised matters are heated with a 

 large excess of hydrate of potash (soda answers 

 equally well), the whole of the nitrogen is ex- 

 pelled in the form of ammonia. In order to 

 render it available for the purposes of analysis 

 the subjoined precautions are requisite. 



3 G 



