3J1 



GASOMETRIC ANALYSIS. 



GASOMETRIC ANALYSIS. 



322 



tube F terminates in the capillary tube k which is cemented into the 

 steel stopcock / ; two platinum wires fused into this tube at m admit 

 of an electric spark being passed through any gaseous mixture it may 

 contain. This tube is graduated into ten divisions of equal capacity. 

 A tube J, open below and terminating above in the stopcock f is held 

 in its place by the clamp n, and can be connected with the stopcock I 

 by the junction piece p. 



The instrument must now be levelled, and the height of each 

 division upon F above the zero point of the millimeter scale on H must 

 be determined by opening their upper extremities and filling them 

 with successive quantities of mercury up to the different divisions 

 upon f, noting at each division the height of the mercury in H. 

 Before use, the cylinder D D must be filled with water, and the interior 

 of the tubes F and H moistened with a few drops of distilled water 

 introduced through the stopcock I and the funnel i. The three tubes 

 being now placed in communication, mercury must be poured into o 

 until it rises into i, when the stopper must be firmly inserted. As soon 

 as the mercury flows from I that stopcock must also be closed. The 

 tube J is then to be filled with mercury and attached by the clamp n 

 and junction piece p to the stopcock I, and a glass tube about 2 feet 

 long passing through the table upon which the apparatus stands, and 

 terminating in a vessel below, being attached to the exit pipe Ji, the 

 instrument is complete. 



In order to illustrate the method of using this apparatus, let us 

 suppose that an analysis of atmospheric air has to be made. Three or 

 four cubic inches of atmospheric air, previously freed from carbonic 

 acid, are thrown up into the tube J, and passed through the stopcocks 

 1 1' into the tube F, a transference which is accomplished by placing the 

 three-way cock / in such a position as to connect F with the exit tube 

 y, through which the mercury flows out as the gas enters above. This 

 operation is facilitated by simultaneously raising the trough c. As 

 soon as the transference is complete the cock I Is shut, and / so placed 

 that F and H are connected with h. Mercury is allowed to flow from 

 h until a vacuum of 3 or 4 inches in length is produced in H and the 

 highest point of the metal in F stands somewhat lower than one of 

 the divisions upon that tube. The cock / must now be reversed, 

 and '/ slightly opened so as to allow mercury to flow into F and H until 

 its highest point in F exactly coincides with one of the divisions. The 

 height of the quicksilver in H must now be exactly determined by 

 reading through a horizontal telescope placed at a distance of about 6 

 feet. If from the number thus read otf the height of the particular 

 division at which the mercury stands in F be deducted, the remainder 

 will represent the true volume of the gas ; since the tension of aqueous 

 vapour in F neutralises or corrects that in n, whilst the temperature of 

 the tubes being maintained constant during the course of the analysis 

 by the water in D D, no correction for variation of temperature requires 

 to be made, and as the tubes in which the volumes are determined are 

 completely shut off from all communication with the atmosphere, the 

 barometrical changes which would otherwise affect the volume of the 

 gases are entirely without influence upon this apparatus. 



Hydrogen in the proportion of half the volume of the air used must 

 now be passed into J, and thence into F, where the volume of the 

 mixed gases must be again determined as before. An electric spark 

 must now be passed through the mixture in F by means of the 

 platinum wires at m. A slight explosion follows, and a considerable 

 contraction in volume of the gaseous mixture also occurs ; this con- 

 traction must be accurately measured by a new determination of the 

 volume of the gases remaining in F. One-third of the contraction thus 

 measured represents the volume of oxygen contained in the air 

 submitted to analysis, and as the air employed consisted only of 

 oxygen and nitrogen, it follows that the estimation of the former gas 

 determines also the volume of the latter. 



Having thus described the construction of this instrument, we will 

 now proceed to notice the methods by which, with its aid, the different 

 gases are separated from each, and the volume of each determined. 



The volumes of the separate constituents of a gaseous mixture can 

 be ascertained either 1st, by direct determination ; or 2nd, by indirect 

 determination. 



1. Direct determination!. 



The chief gases which permit of being thus determined are the 



following: 



Carbonic Acid. 

 Oxygen. 



Olefiant gas, or Ethylene. 

 Carbonic Oxide. 



On the supposition that all these gases were present in a mixture to 

 be analysed, the following operations would be necessary for the direct 

 determination of each. 



First, pass a convenient volume of the gas into the tube J, allow it 

 to pass over into F until the mercury rises into the bend of the capillary 

 tube n I' , and determine its pressure at any convenient mark on the 

 Utter tube ; then pass up into j by means of a curved pipette, one or 

 two drops of a concentrated solution of caustic potash, which will 

 immediately ascend to the top of the tube. Now return the gas into j, 

 and let a quantity of mercury trickle over after it. As the gas 

 depresses the mercury in J, the caustic potash moistens the interior 

 surface of that portion of the tube occupied by the gas, whilst the 

 drops of mercury falling over from it greatly facilitate the action of the 



ARTS AND SCI. DIV. VOL. IT. 



alkaline liquid by bringing every portion of the gas into contact with 

 it. In three minutes the whole of the carbonic acid is absorbed, and 

 the residue must now be transferred back into F for re-measurement of 

 pressure at the same mark upon F, great care being taken that the 

 caustic potash solution does not pass the point between and I' to 

 which the mercury was allowed to rise in the previous transference. 

 The difference between this and the former measurement represents the 

 volume of carbonic acid absorbed by the caustic potash. 



From two to six drops of a strong solution of pyrogallic acid must 

 now be thrown up into J, and the paa being again brought over from r, 

 the oxygen which it contains will be completely absorbed in a few 

 minutes, the liqilid in J becoming of an intense blood-red colour. The 

 re-measurement of the gas, with the same precautions as before, gives 

 the volume of oxygen in the mixture. 



The gas being retained in F, the tube J must be detached from the 

 apparatus, thoroughly cleansed, by washing with water, and then 

 dried, first with bibulous paper, and afterwards by a current of warm 

 air, care being also taken to get the capillary tube perfectly dry. The 

 tube whilst still warm must be completely filled with mercury by 

 immersing it as deep as possible in the well of the trough c, and then 

 applying suction to the orifice of the cock V. Being now attached as 

 before to /, the residual gas in F must be completely drawn over into 

 it, but in such a manner as to avoid the ingress of mercury which 

 might carry over with it some moisture from the tube F. The 

 absorption of olefiant gas must now be effected by introducing into I 

 a coke bullet saturated with a solution of anhydrous sulphuric acid in 

 nordhausen sulphuric acid. The coke bullet is made by placing the 

 bent end of a piece of thin platinum wire in a bullet-mould about half 

 an inch in diameter, then ramming the mould full of a finely powdered 

 mixture of two parts of coke and one of bituminous coal, and finally 

 heating both the mould and its contents to redness for fifteen minutes. 

 The bullet must be removed from the mould so soon as the latter has 

 cooled, and excrescences being removed by a knife, it must be imme- 

 diately plunged into the acid mixture just indicated. The piece of 

 platinum wire serves to introduce it into J, an operation which must 

 be performed with only momentary exposure of the fuming ball to 

 the air, so as to avoid the access of atmospheric moisture, which would 

 combine with the anhydrous acid and render it incapable of absorbing 

 olefiant gas. The absorption of the olefiant gas takes considerably 

 more time than that of the two first gases, and the ball must not be 

 removed from the tube until an hour at least has elapsed. The 

 residual gas is now contaminated with sulphurous acid and the vapour 

 of anhydrous sulphuric acid, from both of which it is however at once 

 freed by passing up into J two or three.drops of concentrated potash 

 solution. The residual gas being again measured in F as before the 

 diminished pressure represents the volume of olefiant gas which has 

 disappeared. 



The remaining gas in the above list carbonic oxide is usually 

 determined by the indirect method mentioned below, there are how- 

 ever certain cases in which its direct determination is desirable, although 

 it is always less accurate than the indirect one. The direct determina- 

 tion of carbonic oxide is effected by absorption with solution of 

 dichloride of copper ; the latter is best prepared by allowing a concen- 

 trated solution of proto-chloride of copper to stand in contact with 

 copper turnings in a closely-stopped bottle for several days. A quantity 

 of this solution, equal in volume to about one-fourth of the carbonic 

 oxide to be absorbed, must be passed up into J, and the gas being brought 

 over from F must be left for five or ten minutes in contact with the 

 solution, whilst a stream of mercury falls through it as in the two first 

 determinations. The pressure of the gas being again measured, gives 

 the volume of carbonic oxide absorbed. 



The determination of any one of these gases in the absence of the 

 others is effected in the same way, viz : 



Carbonic acid by absorption with caustic potash ; 



Oxygen by a mixture of caustic potash in excess with pyrogallic 

 acid ; 



Olefiant gas by anhydrous sulphuric acid ; and 



Carbonic oxide by dichloride of copper. 



2. Indirect dcterminationt. 



The following are the most important gases which are usually deter- 

 mined by the indirect method : 



Carbonic Oxide. 

 Nitrogen. 



Hydrogen. 



Light carburetted hydrogen. 



The estimation of these gases even when all four are present in a 

 mixture, is at once simple, expeditious, and accurate. It consists in 

 exploding a known volume of the mixture in the tube F of the appa- 

 ratus with an excess of oxygen, and then determining, 1st, the dimi- 

 nution of volume of the gaseous mixture after explosion ; and 2nd, 

 the volume of carbonic acid produced by the combustion. The 

 residual gas remaining after absorption of carbonic acid consists of 

 nitrogen mixed with the excess of oxygen previously added ; the 

 volume of the former is of course determined if we estimate that of 

 the latter, which is effected by adding to the mixture of the two gases 

 from two and a half to three times its volume of hydrogen, exploding 

 in F and measuring the contraction produced exactly in the manner 

 already described above for the analysis of atmospheric air. 



