1839.] 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



201 



The letters placed on the right of the second colinnn indicate the 

 authors of the experiments, viz : — D, Dalton, T, I'hilip Taylor, S, 

 Southern, D. A., Dulong and Arrago ; and the numbers in the second 

 column which are followed by a are taken from a table published 

 by CK'mcnt-Desormes, and arc probably calculated, but we have 

 placed them among the experiments fur the sake of comparison. 



On examining this table it will be manifest in the first place that 

 Dalton's experiments above 212 deg. cannot be very accui-ate ; for 

 at 220 deg. both Trcdgold's and our formula give higher numbers, 

 at 272 deg. both give much lower, and at 340 deg. again both give 

 higher numbers, showing a want of regularity in Dalton's results; 

 besides which, the latter difl'er more from other experiments at the 

 above, named temperatures than citlier of the formula, but on the 

 other hand it hardly seems likely that Dalton should have made an 

 error of five inches in 2.31 at 340 deg. of temi)erature, which renders 

 it probable that Tredgold's rule is in excess about that temperature, 

 particularly as it also exceeds Dulong and Arrago's experiments at 

 that and all higher temperatures, the diflerence increasing very 

 ra\)idly with the temperature, as shown in the table, amounting at 

 435.5G deg. to 47'38 inches of mercury, or nearly one atmosphere and 

 seven-twelfths of an elastic force of 24 atmospheres. It appears to us 

 on the whole that Tredgold's rule gives an clastic force which increases 

 too rapidly with the temperature, and consequently that, being exact at 

 212 deg., it gives too low a result below, and too high a result above 

 that temperature, as most of the differences in the table seem to 

 prove, the few exceptions between the temperatures of 2/1.94 deg., 

 and 320..36deg., as well as those at 132 deg., 1 73 deg., and 220 deg., 

 being attributable to inaccuracy in (he observations. The results of 

 our rule, on the other hand, surpass those of experiment below 

 212 deg., and fall short of them, in general, from that temperature to 

 about 360 deg., above which they again exceed the experiments, the 

 differences increasing in an almost unifonn pi'ogression, until at 

 435.56 deg. our formula exceeds the experiments by 19.48 inches, or 

 nearly two-thirds of an atmosphere, which corresponds to a difference 

 of about 2.45 deg. of temperature, while the excess by Tredgold's 

 rule corresponds to a difference of 5.66 deg. 



It is obvious that, our formula being founded on the law of the 

 dilatation of elastic fluids, the results must bear reference to the 

 degrees of the air thermometer. 



MACRAE'S PATENT HYDRAULIC GAS-HOLDER 

 COUNTKRBALANCE. 



Some discussion has lately arisen respecting Macrae's Patent Hy- 

 draulic Gas-holder Counterbalance, assimilating its action to that 

 of the domestic bellows, "regulating the ascending and descending 

 motions of a gas-holder, by means of an hydraulic counterbalance," or 

 " hydraulic tank" as he calls it. 



"The object ef the patent is doubtless a most desirable one. It has 

 long been a desideratum in gas establishments to relieve the gas-holder 

 of a great proportion of its intrinsic weight, while the gas from the 

 retorts is flowing into it ; and, on the other hand, to restore its weight, 

 or as much of its intrinsic weight as may be requisite, while it is sending 

 fortli its contents of gas into the street mains. 



Tlie advantages of these two conditions of the gas-holder are, if 

 attainable, abundantly manifest to the gas manufacturer. It is quite 

 notorious that by the present system the weight and consequent resist- 

 ance of the gas-holder, while it is admitting gas from the retorts, 

 several parts of the machinery arc materially injured ; time is lost in 

 charging tlie gas-holder, a very unnecessary (piantity of fuel is con- 

 sumed in the furnaces, and the gas is not only wasted, but, by not 

 being allowed to escape from the retorts with sufficient rapidity, it is 

 deteriorated, in its illuminating properties, by being exposed too lon'^ 

 to the intense heat of the retorts. Frequent and dangerous reactions 

 are also produced from the same cause. 



Many attempts have been made, at various times, to obviate these 

 defects, and, with that view, patents have been taken out by Messi-s. 

 Malam, Outhot, Parks, and Broadmeadow. They have all been fail- 

 ures, audwe very mftch apprehend that the contrivance ol' Mr. Macrae 

 will not turn out to be a bit more successful than the schemes of his 

 predecessors. 



The chief ^objections to it are, 1. That, if there be no natural head 

 of water existing above the utmost height to which his " hi/draitlic 

 tank" will rise, there will necessarily be imposed the labour of pump- 

 ing up water every twenty-four hours to this height, in order to fill 

 the " hydraulic tank" every time the gas-holder has to be charged with 

 gas. '2. That this " hydraulic tank'' must necessarily discharge its 

 contents of water, so far below the surface of the water in the ^aso- 

 meter lank, as to require another process of pumping in order to get 

 rid of it. 



Under ordinary circumstances, therefore, here are two operations of 



pum[)ing every twenty-four hours ; the one in charging, the other in 

 discharging the gasometer. After this, it would appear to be entirely 

 out of the question to add to the labour (as Mr. Macrae suggests) by 

 " supplying the required weight of liipiid to liis hydraulic tank, every 

 time the retorts are drawn." 



It will hardly be credited that for a single gasometer of 50 feet in 

 diameter, by '22 feet deep, and working at an inch pressure, an hy- 

 draulic tank, on Mr. Macrae's jilan, if of a cylindrical shape, would 

 require to be about 4t) feet below the surface of the water in the gaso- 

 meter tank ! — or if it were a cube of two feet by six feet, still its depth 

 below the surface of the water in the gasometer tank, would require 

 to be 17 feet— either of these depths being considerably below the 

 surface of the ground, consequently requiring the water to be pumped 

 out every time the hydraulic tank empties its contents into these shafts, 

 or wells. 



To show that there is no exaggeration in this, it is well known that 

 the ordinary balance-weights for a gasometer of the dimensions we 

 have supposed, working at an inch pressure, would require about 13 

 cubic feet of cast iron, independently of the chain, or a cube of 2 feet 

 X 2 feet X 3.3 feet. If this balance weight, however, were to be made 

 after Mr. Macrae's plan, and instead of being composed of a solid 

 cube of cast-iron, it consisted of a box, fdled with water, its dimensions 

 would be 2 feet by 4 feet, and 1 1 feet deep : for if we take 5943 lbs. as 

 the weight of the 13 cubic feet of iron, and allow 468 Uis. for the 

 weight of the box to contain the water, and divide the diflerence by 

 62'5 lbs., the weight of a cubic foot of water, it will give 87 cubic 

 feet as tlie dimensions of the box, 

 5943—461 



63-5 



=87 cubic feet 



or 528 gallons. This is the weight only of the balance weights at 

 2>rcscnt in use. But it is to be supposed, that Mr. Macrae proposes to 

 use a much greater weight as a counter-balance than this : perhaps 

 J or i of the weight of the gasometer. In cast iron, then, t would be 

 equal to 28 cubic feet, and 'J08 cubic feet, or 1 ,248 gallons, if tilled 

 with water, including its containing box, or hydraulic lank. Now it 

 has been already stated, that a cylinder adequate to hold the necessary 

 (piantity of water, according to Mr. Macrae's plan, would require to 

 be 40 feet below the surface of the water, in the gasometer tank. 

 But if the cyliader were only 2i feet in diameter, it would require to 

 be ?nore than 40 feet in depth .-' for 2.5 X 2.5 X 11 = 4.91 X 40 = 



14 

 I9G.40 cubic feet only, instead of 208 cubic feet. 



It will be quite obvious, that if the water discharged into this well, 

 of upwards of 40 feet in depth, be not pumped out of it before the 

 gasometer begins to fall, the gasometer will be able to descend only a 

 few inches, until it become stationary : for the still undischarged load 

 of the counter-balance (being i of the whole weight of the gasometer), 

 will prevent it from descending further. 



Mr. Macrae's scheme, though crude and unsuitable, is not without 

 a considerable portion of ingenuity. The object aimed at is decidedly 

 one of great importance to the gas manufacturer. A. 



The OxJ'ord-sirccl Expcrimentat Paving. — On Saturday, the 18tli ullimo, in ac- 

 cordance witli the arrangements made by the Marylebone Vestry, limiting the period 

 ul' the trial of the respective experimeutJll pavements laid down in Oxford-slreet nn- 

 tit thenioutli ot* May, Mr. Kensett, as i-liaimian of the Paving Committee, laid before 

 tlie board the state in which each of the experiments was. The following is the 

 resnlt : — On examining the bitumen laid down by the Bastenne and Gaujac Bitumen 

 Company, they found it had stood the test of the severe wear and ttiar of llie vehi- 

 cles passing that road during the whole winter, without any material alteration, 

 'i'laat portion laid down by tlie Val dc Travers Company, whicli bad been studded 

 with stone, had stood, but that portion in which the broken granite had been set in 

 tlieir liquid had totally failed, and must be removed immediately Tlie Aberdeen 

 granite cubes laid down by tlie parisli Iiad proved to be in most excellent condition ; 

 that more particularly wliich had been set in Claridge's .\spbalte was in a state of 

 superior order, and the stones appeared immoveable. Robinsons l>itumen had been 

 taken up some months since in consequence of liaving proved a decided failure. Tlie 

 ScotcJi asplialtimi had been repaired once, and had again becoJue so ililapidated as to 

 render tlie portion of the road wliich it occupies dangerous. The wooden block 

 pavement, wliicli had !>een laid down live mouths since by the projector, Mr. Stead 

 liad excited the minute attention and admii-ation of the committee. It appeared, on 

 examination, that tlie blocks formed a road of a most even surface, and carriages 

 passed over without tlie slightest noise, and of tlie 12 inches, the length of the 

 lilocks, it Wiis found they had not been dimini-shed one rpiai'ter of an inch. Tlieir at- 

 tention, however, was particularly dirccteil to the bottom of the blocks, whicli, to 

 liio extent of about three-fourths of an inch, appeared discoloured by a blue stain, 

 intimating (?) that the lirst approach of decay was making its appearance. .*V con- 

 siderable. division of opinion c.visted among tlie coimnittee upon the above appear- 

 .ince being that of decay ; they were, however, of an unanimous ojdnlori that a fur- 

 ther trial was necessary, in order to enable the vestry fairly to be satisticd as to the 

 durability of the pavement which might ullirdately \)c decideil upon, and that any 

 decisioiwiught to be deferred till the autunin. It was ultimately rieciiled in the 



\c.>try that the application of a ]\Ir. ticary to lay down a w ten pa\ement. upon an 



improved principle, should he reitjrred to the coumiiltee, and that the Uual decision 

 upou the experiments should be deferred to the first Saturday in September. 



