156 



CHEMISTRY. 



Pt 



Chemical ed, open below Ind shut above, as those rrpresrrted in 

 v _ Plate CX LI.; and in Fig. 1. Pl.ttr CXl.II. 



I. When the quantity of gas prepared is consid.rable, 

 r\a r. it is necrssary to be provided with larger venseU than 

 tif. 16, 17. any of those already mentioned to contain it. Such ves- 

 sels ire usually mad.- of tin plitc japanned, or partly of 

 tin-platr, partly of glass, and they are known by the 

 name of gazomrtert, gat ImUcrt, air holders. Their con- 

 struction is very various, according to the fancy of the 

 chemist, or the object which he has in view. We shall 

 give a description of some of the most useful. 



Fig. 3. and 4. represent the outline of a very convc- 

 Ki" '* 4. n ' lfn * vessel for holding oxygen gas. It is made of tin- 

 plate, well japinned, both withinside and without. It 

 may be of any si/- : the vessel, of which this U a re- 

 presentation, held about '.I XXI cubic inches. It is a cy- 

 lindrical vessel, close on all sides, md ought to be pret- 

 ty strong to resist the pressure of the atmosphere, which 

 tends to force out gas, or to force in air according to 

 the changes in its density which take place. It is fur- 

 nished with three mouths, A, B, C. The first at the 

 top, the second at the side as high up as possible, the 

 third at the bottom. A and B are each provided with 

 a stop-cock. The stop- cock A is soldered into the 

 tube D, which goes to the very bottom of the vessel to 

 which it is soldered, in order to increase the strength of 

 the air-holder. The tube D, towards if bottom, 'u 

 perforated with a number of holes. To the extremity 

 of the stop-cock B, the piece of bent tube E is ground, 

 so as to be air-tight, but to move freely round the ex- 

 tremity of B, which is turned up to receive it. And 

 to the extremity of E, the long tube F is likewise 

 ground, so as to be air tight, yet capable of moving 

 freely. These two tubes, by their motion, form an uni- 

 versal joint, so as to enable the operau-r to turn the ex- 

 tremity of the tube F any way he thinks proper. The 

 mouth C consists of a tube about an inch in diameter, 

 introduced into the vessel, near the bottom, at an angle 

 of about 45. It is provided with a stopper, which 

 screws into it and shuts it close G is a glass tube, fix- 

 ed into the top and bottom of the air-holder, and gra- 

 duated. The use of it is to shew the operator how much 

 gas the vessel contains. It is a large glass conical ves- 

 sel, made to fit into the upper end of the stop-cock A. 

 A few words will explain the method of using this 

 vessel. The first step is to fill it with water. For this, 

 the mouth C must be shut, and the stop-cocks A and B 

 opened. Water is then poured into the glass vessel H, 

 which, running down the tube D, makes its escape 

 through the holes in its bottom, and fills the vessel, while 

 the common air makes its escape by the stop cock B. 

 When the air-holder is quite full of water, the stop- 

 cocks A and B are to be shut, the glass vessel H re- 

 moved, and the stopper of the mouth C removed. As 

 the vessel is completely air tight, the water cannot make 

 its escape by the mouth C, because the angle at which 

 it enters the vessel, prevents any common air from en- 

 tering. The mouth of the tube connected with the ap- 

 paratus for furnishing oxygen gas being introduced into 

 C, the gas rises gradually to the top of the air-holder, 

 aad the water runs out by the mouth C. When the pro- 

 cess is finished, the mouth C is to be shut ; and it the 

 vessel be a good one, the gas may be kept iw it for many 

 months without undergoing much alteration. Suppose 

 we want a portion of the oxygen gas out of tlr.s air- 

 Lolder, for any particular purpose, we have only to in- 



troduce the point of the tube F into the mouth of the Chemical 

 vessel which we mean to .contain the oxygen gas, and ApP 1 " 1 "'- 

 then to pour a quantity of wjit-r into the glass vessel H, ' ^~Y~"" 

 which must be replaced d-r 'he piir;M>s<-. The stop- 

 cocks A and B being opened, the water runs down the 

 tube D, and forces t' . scape through 



the tube F. By this method any quantity of the gal 

 wanted may be easily procured. 



Another ga/.ometer, of a difF<-rent construction, is re- PLAT* 

 presented in Fig. 3, 4 wnii !. are m.tily different -MI. 



of the same vessel, and the same letters in butli refer to f 'S- 3 > ^ 

 the same parts. Like the former, it is made of tin-plate, 

 well japanned, both within and without, aa is the out- 

 er pai!, or circular ve.^el, v.-ith a sjv^ut at top. Two 

 tubes, t/and f, (each filled with a stop-cock externally), 

 are firmly boldcred to the sides of the pail : thr tube rf 

 penetrates at the bottom of the pai', and proceeds to 

 the centre, whore it joins the termination of the tube e, 

 which enters the top of the pail, and proceeds down- 

 wards ; and from the place of junction, the upright tube 

 g ris'-s through the middle of the pail, a little above the 

 level of its upper rim. The vessel b is a cylinder, open 

 only at bottom, and of less diameter than the pail into 

 which it is inverted, and can move up and down freely. 

 This cylinder has a solid stem, c. which passe. 1 - through a 

 holeii. the wooden crossbar of the frame, round the top of 

 the pail, and serves both to keep the cylinder in a perpen- 

 dicular direction when moving up and down, and to indi- 

 cate the quantity of inclosed gas by the graduation on 

 its surface. The weight of the cylinder is counter- 

 poised by weights put into a scale dish, which is con- 

 nected with the top of the cylinder by a cord and pul- 

 ley. The pail ha* besides an opening through its bot- 

 tom, closed by a separate stop-cook, f, by which the 

 water may be drawn off. The whole apparatus is con- 

 veniently supported on a heavy wooden stool. To use 

 this gasholder, first let the cylinder fall to the bottom 

 of the pail, and pour \r;itcr into the spout of the latter 

 till it is quite full ; then shut the cock e, and open rl, 

 and connect with it the tube which conveys the gas im- 

 mediately from the retort or other vessel in which it is 

 produced : or, if more convenient, shut rf, and convey 

 the gas through e. The gas rises through the upright 

 tube g, to the top of the cylinder b, which it gradually 

 lifts up; and care must be t. ken to keep in the scale-dish 

 sufficient weight to allow the cylinder to move with per- 

 fect freedom. When all the gas wanted is obtained, shut 

 the stop- cock, and it remains in the air holder till want- 

 ed. To take out any of it, connect with either of the 

 stop-cocks a bent tube, and insert the mouth of it into 

 a vessel destined to receive the gas, remove the weights 

 out of the scale-dish, and open the stop-cock. The 

 weight of the cylinder b will press out the gas and fill 

 the vessel. 



As the weight of the cylinder is constantly increasing 

 during the whole of its rise out of the water, it is ne- 

 cessary to be continually adding weights to the scale- 

 dish to compensate for this increase, otherwise the ga 

 will be more and more compressed, and at last will cease 

 to enter altogether. Or this increase may be still bet- 

 ter compensated, by making the cord pass over a spiral 

 pulley, by means of which, the weight in the scale-dish 

 will act more and more powerfully as the cylinder rises, 

 and thus compensate the increase of its weight. 



Many other gas holders have been contrived by che- 

 mists ; but it it needlebs to describe them, as they may 

 9 



