or 15 hours, at the rate of about 0.3 or 04 foot per hour. The rate of flow is readily regulated by a few observations, of ten minutes each, of a meter at the tail of any train. A little practice enables the rate to be judged of closely enough, by the size of the flame burning from a small straight glass tube at the tail of the apparatus, as shown in Fig. 4. The preparation for the final weighings is here the important part, and indeed the only troublesome part of this analysis. Fig. 3 repre E H U FIG. 3. C Supplementary Arrangement for Completion of Process in the Train, shown by Fig. 1. sents, as aforesaid, the mode of attaching the preparatory train to Fig. 1, for this final operation, or rather succession of operations. D here represents a new tube introduced at this time, which is an ordinary form of CaCl tube, but having its smaller extremity bent at an obtuse angle, as shown, and which contains near its upper end a slip of turmeric paper, and has, moreover, running through it from end to end, and projecting an inch at each end, a small flexible copper wire ; the object of which latter is to clear a passage through the crystals of naphthaline which condense in this tube at a subsequent stage of operations.* *This wire should have been shown more distinctly in the cut, but this is only one of several unfortunate defects in these cuts.-H. W. After this disposition of the apparatus has been made-D having been of course weighed with its appendages, and the jar of ice N (which is no longer of use) removed, the meter being connected directly with M—the first step is to distill over, at a very low temperature (unless saving of time is important, at ordinary temperatures) in the current of gas from the preparatory train-which generally in this case may flow even as rapidly as two feet per hour-all the volatile ammonic carbonate and sulphohydrate that has condensed in the flask C and cotton tubes E and F. The volume of gas required to effect this may be double (or even more) that from which the liquid was condensed. It ought to have been stated that the total amount of crude gas analyzed by this apparatus should not exceed ten cubic feet. This volume is within the limits of manageability, but generally somewhat less is probably advisable. With a rapid current of gas, this complete transfer of the volatile ammonia-compounds will be found to have been effected during 15 or 18 hours; but sometimes more time is required; and it is better to allow 24 hours for this part of the process. If an attempt to hasten it is made, by immersion of the flask in warm water, constant watching is necessary, as naphthaline then enters upon the scene, and may at once clog up all passage. The complete transfer of the ammonia is indicated by the return of the slip of turmeric-paper to its natural color. As, in my experience so far, this liquid always contains chloride of ammonium, and possibly sulphite and other non-volatile ammonia salts, those who wish to transfer all the ammonia to the bisulphate-tube G, must introduce into the flask a weighed quantity of dry hydrate of soda. When the ammonia-transfer has been completed, the flask C is immersed the gas-current being continued-in water sufficiently hot to volatilize the naphthaline, which will condense in crystalline form, together with water, in the tube D. The wire running through D now comes into play; and, in fact, without it, naphthaline would here become as great a cause of difficulty as it often does in the distribution of coal gas. When clogging occurs, the gas-current is stopped, the rubber connector between D and E detached, and the wire moved up and down or twisted round. With careful management, two hours work and some two feet of gas from the preparatory train, will suffice to transfer the naphthaline to D, which is then detached and weighed again. To remove the intermixed water from the naphthaline, the lower end of D is stopped, the cork and tube removed from the upper end, the wire coiled within, and this upper end connected by a wide short rubber-connector with the open end of a test tube containing some granulated CaCl. When dry, the cork and tube are restored, the stopper removed, and the weight again ascertained; the variation now from the first weight is the naphthaline, so far as it can be saved by this mode; which of course is imperfect, but is the best that I have so far succeeded in devising.* The flask C, still containing tar and water is then removed likewise from the arrangement-the stoppers DD (Fig. 1.) being applied -and then H of the preparatory train is connected directly with the first cotton-tube E; the gas-flow being resumed. Some five feet more of dry gas may be now required to transfer all the moisture to the CaCl tube between G and H (omitted from the cut.) The water and tar in the flask C must be separated by careful distillation at a very moderate temperature, and in estimating the weight of the residual tar, account must be taken of the sodic hydrate that was added, as above, to eliminate the fixed ammonia. The point at which the whole train becomes dry and ready for the final weighings, is readily perceived by a practiced eye. One indication is a faint superficial whitening of some unaltered blue granules (if any) of cupric sulphate in the tube HJ. Several other indications might also be cited. IV. OF THE GENERAL MANIPULATIONS WITH PURIFIED COAL-GAS. Fig. 4 represents a very complete train for this purpose. As the suspended matter here is absent or trifling in amount, and the ammonia usually very small, A represents a combined arrangement for taking up both these. The first or right hand U-tube is loosely filled with cotton, the second one with granular bisulphate. E contains two slips, of turmeric and red litmus paper, to verify the perfect efficiency of the bisulphate. F contains granulated cupric sulphate crystals. G is CaCl. H is sodic hydrate, with a small CaCl-tube appended. The arrangement KL, for determining oxygen, requires special explanation. K contains glass beads or broken-up lass rod, wet with a concentrated solution of pyrogallol in previously-boiled water. L contains CaCl. As, in order that the pyrogallol should * Since the above was first presented to the Gas-light Association, I have discovered that very appreciable additional traces of naphthaline con lense, and remain throughout the final desiccation, in the cotton-tubes E and F, and have therefore been rated as solid matter mechanically suspended.-II. W. take up the oxygen, there must be an alkali present, the following special course is adopted for preparing KL for initial weighing and introduction into the train. K is immersed, L being detached for the time, in snow and salt; and connected with a flask like C in Fig. 1, containing some of the strongest liquid ammonia. A current of common street gas is then directed first into the ammonia flask, then through K. The former is warmed, and the as gas, it issues from the latter, lighted. The point of saturation of the contents of K with NH3 will be indicated by a change in the character of the flame. The ammonia-flask is then detached, K being simultaneously-to prevent ingress of air-attached to J, L replaced, and the whole put in position. A, in connection with E, is also dried out before initial weighing of the former, by a current from the Preparatory Train; this operation being greatly accelerated in this case, by immersion of A in the boiling water in B, which is raised up and hung, for this purpose, on the little wire pothook D. It is to be observed that the two tubes in A are weighed separately, and not together; and to avoid hygroscopic moisture, cooled and enclosed while weighing, in close boxes of sheetbrass or tin. The members of this train G, H, and P require no preparatory desiccation before weighing. With reference to the tube P, a special remark should be made. The hygrometric equilibria of the cupric sulphate in the aerial and the gaseous media respectively, may appreciably vary, even at the same temperature. A safe plan, therefore, before initial weighing of this tube, will be to pass through it a current of the gas to be analyzed, for a few minutes. This will serve also as a useful qualitative test, in advance, of the amount of HS present. When the HS is very minute, as it should be in a well-purified street-gas, there is another method available, which I have often used, and which may be preferred, as surer. I find if the granulated bluevitriol be spread out in a gentle sand-bath heat, for some days, it loses most of its water, turning white and chalk-like, without falling to powder, and will now still absorb H S readily, even though the latter be absolutely dry. If F be charged with such dehydrated cupric sulphate, it may be introduced after the CaCl-tube G, instead of before, and will there absorb from the gas only HS. If it has lost as much as three-fifths of its water, it will not impart any moisture to the gas at ordinary temperatures. (To be Continued.) |