350 



THE CIVIL ENGINEER AND ARCHITECTS JOURNAL. 



[October, 



London, differed from that of almost all other places, because the material 

 employed was not pure clay ; it was a substance nearly resembling loam, of 

 a slightly cohesive nature, which would not admit of its being used in the 

 natural state and burned in close kilns with coal, but that with an admixture 

 of ashes it became sufficiently tenacious to be formed into bricks ; the ashes 

 performing the same office as the chopped straw did, in those made by the 

 ancient Egyptians. Of the sixteen hundred millions of bricks made annually 

 in England and Wales, about one-fifth part only was made according to the 

 London method, with a mixture of ashes. As to the density, he did not 

 think that the weight of bricks should be received as an iiu!?x of their quality ; 

 for bricks made by exactly the same process and equally compact, would be 

 heavier or lighter, as they were made of strong or of mild clay, and yet their 

 strength would be equal. 



Mr. Pellatt observed that nearly if not all argillaceous or aluminous earths 

 were, with certain modifications or admixtures, suited for making bricks. 

 The term silicate of alumine, might include the various earths, whether deno- 

 minated clay, marl, loam, argile, &c. The best fire bricks were made from 

 native clay, containing alumine combined with a large proportion of silex. 

 The cohesive or plastic property arose from the former, but too much of it 

 rendered the bricks fusible. As most of the common clays contained a large 

 proportion of alumine, with occasionally lime or other fusible substances, a 

 mixture of coarsely pulverised burnt clay, sand or cinders, became necessary, 

 in order to counteract that tendency. Alumine had a great affinity for silex, 

 as well as iron and sulphuric acid, and the large use of cinders as a mixture 

 with the London clay might be accounted for, not only as it reduced the 

 proportion of alumine to other substances, but because it had a tendency, 

 when submitted to heat, to carbonize the sulphates, aud to diminish the 

 fusibility of the brick. Bricks made of common clay could not be burnt 

 under the same high temperature as fire bricks, and they contracted much 

 more in burning. All dry substances, which were used to decrease the pro- 

 portion of alumine, in making bricks or crucibles, were included by the 

 French under the general term of " ciment." The most useful properties of 

 "ciment," when well pugged or kneaded with the clay, were to hasten the 

 drying, and to diminish the contraction, and the consequent risk of breaking 

 in the kiln : the addition of " ciment " was economical for fire bricks, par- 

 ticularly when they were manufactured at a distance from the mines ; the 

 fire clays of Stourbridge, Newcastle, and Glasgow, were found amidst the 

 coal strata ; Stourbridge clay was the most esteemed, and when carefully 

 picked, ground, sifted, &c., would bear, for brick-making, two proportions 

 (by weight) of burnt clay or " ciment " to one of native clay. The sagger 

 clay from the Staffordshire potteries was also a fire clay, and was well suited 

 for making tiles or bricks of a compact character, but was probably more 

 liable to be vitrified than the Stourbridge clay. China clay, or the "kaolin" 

 of the Chinese, was decomposed felspar, called in the potteries "Cornwall 

 ston";'' the undecomposcd felspar was interposed with it, and used by the 

 French and the Chinese as porcelain glaze, the term used for it by the latter 

 was " petuntse." The constituents of " kaolin " were — 



According to Dr. Ure. 



Murrav quoted 

 •i. ,. , , • \auquehn s analysis 



\ auquehn s analvsis — » ,, H „, ; , 



Murray stated 



uquelin's analys 



of Hessian Clav to be 



Mr. Parkes believed that in addition to the ashes giving a cohesive charac- 

 ter to the material of which the bricks were composed, they were of advan- 

 tage in the process of burning, because they enabled the fire to spread 

 gradually from the lower tiers, through the mass in the kiln, without per- 

 mitting an intense partial beat, such as sometimes occurred where coal alone 

 was used, the effect of which was, that all the bricks around were vitrified 

 and their surfaces became glazed. He had given some attention to the 

 subject, and had tried experiments, by ascertaining accurately the quantities 

 of ashes and of water which were incorporated with the loam in a certain 

 number of bricks, and had found that the evaporation, during the process of 

 burning, exceeded that of any steam boiler, as it amounted to as much as 

 14 lb. of water by 1 lb. of breeze. The mode of making bricks near London 

 was peculiar to the district, and the workmen did not understand any other 

 method ; the blue clay was not used because they did not know how to work 

 it. In a work published by Mr. Aikin, 1 which was a selection from the 

 papers read before the Society of Arts, the subjects of brickmaking and 

 pottery were very correctly treated. 



Mr. Dickinson observed, that the ashes used in making stock bricks, could 

 not supply the place of the straw now discovered in the Egyptian bricks, 



• "Illustrations of Arts and Manufactures," by Arthur Aikin, p. 1", 

 12mo. London, 1841. The paper, with additions, was published in the 

 Journal fur October, 1841 , vol. iv. p. 340. 



because the process of burning would have destroyed the straw as it appeared 

 to do the ashes ; he had burned bricks extensively in clamps and in kilns, 

 and it appeared to him that the ashes assisted in fluxing the brick earth, for 

 on breaking a good stock brick it was always found that the interior appeared 

 to be vitrified, and was extremely hard, and he remarked, that if the ashes 

 worked in with the clay in pugging, either exceeded or fell short of the 

 ascertained proper quantity, the bricks were fragile and less durable. 



May 9. — The President in the Chair. 



" Observations on the periodical drainage atid replenishmmt of the sub- 

 terraneous reservoir in the chalk basin of London." Continuation of the 

 paper read at the Institution, May 31st, 1842. = By the Rev. J. C. Clutter- 

 buck, M.A. 



The author commences by answering an objection founded upon a passage 

 of Conybeare aud Phillips' Geology Book 1, chap. IV. sec. 11) which was 

 urged against his former statements. The water, it was said, appeared to 

 rise in different places to different heights — at Mile End it stood at the level 

 o:" high-water mark in the Thames ; at Tottenham 60 ft. ; at Epping 314 ft. ; 

 and at Hunter's Hall, two miles beyond Epping, at 190 ft. above that level. 

 Especial stress was laid on the height to which the water was supposed to 

 have risen in the well at Epping, namely, to within 26 ft. of the surface, 

 and to 314 ft. above high-water mark. It appeared from a note appended 

 to the statement referred to, that the first 27 ft. from the surface of this 

 well consisted of gravel, loam, and yellow clay, and that after sinking 200 ft. 

 and boring 220 ft., as no water was found, it was considered a hopeless 

 labour, the boring was discontinued, and the well covered over; that at the 

 end of five months, it was found that the water had risen to within 26 ft. of 

 the surface; from which it might be inferred, as was afterwards proved, by 

 information obtained from the owner of the well, that this supply of water 

 was to be attributed to a landspring, and was not derived from the sand of 

 the plastic clay formation, to which the boring had not penetrated. Having 

 thus answered this objection, it is shown that a line drawn from the water 

 level at Hunter's Hall to mean tide level in the Thames, 10 ft. below high- 

 water mark, would cut the level in the other wells, and give a water level 

 dipping at an average inclination, very nearly coinciding with that insisted 

 on in the statement to which the objection was raised. It appeared that the 

 difficulty of determining the exact dip of the water level between the river 

 Colne and London, had in some measure been removed, by the sinking of 

 three wells in the direct line of the author's observations, namely, from the 

 river Colne one mil© N.E. of Watford, in a straight Hue to Edgware, and 

 thence by the high road to London ; the information thus obtaiued, proved 

 the general correctness of the author's former calculation as to the line that 

 would represent the natural water level. It is then shown that a line drawn 

 from a point three miles south of the Colne, at the level of that river, or 

 1 70 ft. above Trinity high-water mark, to mean tide level in the Thames 

 below London Bridge (a dip of about 180 ft. in 14 miles, or an average in- 

 clination of 13 ft. in the mile) cuts the water level at the point whence it is 

 drawn, at Hendon Union Workhouse, and at Cricklewood, between that 

 place and Kilburn, whence it may be inferred that up to this point there is 

 no apparent trace of a depression of level caused by the exhaustion of water 

 under London. ■' At Kilburn, the water level (which is known to have stood 

 some years since about 20 ft. higher than at present) is considerably de- 

 pressed below the line so drawn, which depression may lie attributed to the 

 influence of the London pumping — it is suggested, that it is desuable that 

 the wells on the confines of London, and throughout the district, should be 

 periodically measured, to ascertain at what distance, and in which direction 

 this yearly increasing depression may be found to extend. The author pro- 

 ceeds to describe a phenomenon connected with the periodical replenishment 

 of that portion of the London basin which underlies the London and plastic 

 clays, and whicli cannot, as in the upper or chalk district, be fed by infiltra- 

 tion. This phenomenon is by him called the " oscillations of the water 

 level," caused by the irruption of rain water, which runs from the surface of 

 the London and plastic clays, and which sinks into the subjacent chalk 

 through " swallow holes," on its arrival at the outcrop of the sand of the 

 plastic clay formation. This point of irruption lies to the southward of the 

 river Colne, and forms the line of demarcation between the clay and chalk 

 portions of the surface of the London basin, leaving a belt of the latter 

 varying from two to three miles, or more, in width, between the river and 

 the outcrop of the clays. The water level rises to a point within the out- 

 crop (called the fixed summit level) at an angle of not less than 10 ft. in the 

 mile, when most depressed by the springs ; below an angle fixed on as the 

 lowest line of inclination to which the water in the chalk will fall. From 

 the fixed summit the level declines towards London ; in the line taken, it is 

 found at the level of the Colne, three miles from the river. After heavy 

 rains, when the clays throw the water from their surface, the irruption of 

 water may be seen at the outcrop of the sand of the plastic clay formation ; 



2 Minutes of Proceedings, Journal vol. V. page 385. 



3 The surface levels on this line having been obtained, and a section having 

 been made, the line drawn from the two points, namely, three miles south of 

 the Colne, to mean tide level in the Thames, enabled the author to determine 

 the height to which the water was found to rise at Hendon Union Work- 

 house and at Cricklewood (the only points at which the height of water 

 could be ascertained) in both cases to within three feet. 



