If a purifying apparatus were constructed, in which the properties of figs. 6 and 8 were combined, it would probably be found more complete than any one at present in use; the essentials being a constant supply of lime-cream, and its proper application ; and the means of making the machine, by its com mon action, keep itself free from obstructions by the clogging and adhering of the lime to its different parts.
The quantity of lime necessary to purify a given bulk of gas will no doubt vary considerably, ac cording as the coal used is more or less free from admixture with impurities, affording sulphureted hy drogen gas on distillation: the weight of lime, com pared with that of the coal distilled, has been stated at from 1-30th to 1-10th, but the application of tests from time to time to portions of the gas, will be necessary in order to know what proportion of the purifying mixture ought to be employed. By forcing a quantity of gas through a weak solution of acetate of lead (formed by dissolving three or four grains of it in a two ounce phial of water), the natural milkiness of the solution will assume a dark cloudy appearance if sulphureted hydrogen gas is present. Water impregnated with this gas assumes a black appearance on the addition of a drop or two of nitrate of silver. A current of gas containing sulphureted hydrogen, directed against the surface of a card or other substance which has been paint ed over with white lead ground up with water, will immediately discolour it.
A patent has lately been obtained for purifying coal gas by passing it through strata of recently slacked lime•in a nearly dry state. With regard to the actual absorbent powers of lime, as exposed to the presence of sulphureted hydrogen gas, no accu rate accounts appear to have been published; but it is not probable that the performance can equal that effected by an equal quantity of lime made into cream, and differently applied.
Journal, No. 16); and, in 1819; Mr D. Gordon ob tained a patent for a similar apparatus.
A variation from Lavoisier's gasometer has lately been used in some gas-light works, in which the pul leys and counterbalance are omitted, and the invert ed vessel kept in a vertical position by guides which allow of its rising or falling, as the gas is forced in or suffered to escape. This is a very imperfect ma chine, as subjecting the gas to a varying pressure, and which has, therefore, to be regulated, as will be shown hereafter. Other constructions have been
proposed and employed, also subject to the irregu larity just mentioned.
In all cases where a steady light is required, it is of importance that the supply of gas be uniform, and therefore requisite that the pressure or force with which it is expelled the gasometer, should be always precisely the same. A gasometer on the construc tion first above mentioned is represented in Plate LXXXIII. fig. 1, where a a is the vessel for contain ing the gas, inverted over a cistern of water b b ; and suspended from the pulleys c c, by means of the chain d, and counterpoise e ; ff are tubes for bringing in and conveying away the gas.
The gasometer, like any other body, immersed in water, of course loses a portion of its weight equal to that of the water which it displaces ; and it has therefore the less power to expel its gaseous contents the deoper it is immersed. To remedy this irregu larity, additional weights are added from time to time to the gasometer as it descends, and removed again as it rises ; but this method, though at present in prac. tice in some places, is very imperfect and trouble some.
lbs.
Then, when the gasometer is immersed, its ef fective weight is 900 To which must be added the portion of chain now acting, as increasing the weight (of the gasometer), 50 The sum corresponds with the actual weight of the counterpoise, f 950 Again, let the gasometer be elevated out of the water, its actual and effective weight then is 1000 To balance which is opposed the coun terpoise, 950 And the portion of chain now removed to the other side of the pulley on which the counterpoise is, and acting with it, 50 — •— The sum corresponds with the actual weight} 1000 of the gasometer, This method, though it effects the purpose of Reservoirs or Gasometers suitable for containing the Gas.