1843.] 



THE CIVIL ENGINEER AND ARCHITECTS JOURNAL. 



319 



cavities on the surfaces were desirable, but if the bricks were good and 

 stronger than the cement, the cavities were not necessary. 



Mr. Farcy exhibited specimens of tiles, eVc, made by Mr. Prosser, of Bir- 

 mingham, and described the process of manufacture. The clay was first 

 dried upon a slip kiln as if for making pottery, then ground to a fine pow- 

 der, and in that dry state it was subjected to heavy pressure in strong metal 

 moulds : by this means it was reduced to about one-third of its original 

 thickness, but the clay appeared to have contained sufficient moisture to give 

 it cohesion, and the tiles retained the most perfect sharpness at the edges — 

 they were then carried direct to the kiln, and baked in " saggers " or cruci- 

 bles, without any previous drying, and they did not appear to crack in baking. 

 A brick of the usual dimensions, which was exhibited, had been made by 

 this process from the common brick-earth of Staffordshire, ground fine : it 

 was of a clear red colour and of homogeneous texture, and the edges were 

 sharp ; its weight was 6J lb. and the specific gravity was 2-5.* Mr. Farey 

 stated that this brick was not vitrified, but merely baked, and that it bad 

 acquired its density from the great pressure used, which was equal to 250 

 tons. 



Mr. Pellatt had seen Mr. Prosser's machine at work, making buttons and 

 other small objects ; the ground clay appeared to retain a certain degree of 

 moisture which, combined with the pressure, gave it such tenacity, that on 

 leaving the mould it could be handled and carried direct to the kiln; it was 

 compressed to about one-third of its original thickness. 



The clay of the Staffordshire potteries contained chiefly silicate of alumine ; 

 it was principally valuable for, and was employed in, making "saggers" or 

 crucibles wherein the china was baked. The clay from which the china and 

 crockery-ware was made, was brought from Devonshire, Dorsetshire, and 

 Cornwall, and was used with certain mixtures of silex and other substances 

 according to the manufacture. 



Mr. Blashfield stated that of the specimens of Prosser's manufacture on 

 the table, the small hexagonal tile 3} inches diameter and three-eighths of an 

 inch thick, had sustained a pressure of 30 tons, without the edges being 

 crushed ; another of the" same diameter and 2-J inches thick, bore 35 tons, 

 and the 9 inch stock brick remained perfect under a pressure of 90 tons : 

 the largest sized slab hitherto produced by the process was 34 inches long 

 by 8 inches wide, and half an inch thick : but he believed that as soon as 

 the new hydraulic presses were completed, it was Mr. Prosser's intention to 

 make large bricks of varied forms for architectural purposes. 



In reply to a question from the President, Mr. C'owper explained that the 

 tiles, &c, after being subjected to the pressure, were released by the action 

 of a treddle, which raised the bottom of the mould, and thus brought out 

 the object without injuring its edges. 



Mr. Hunt exhibited a model of the brick-making machine (see Journal 

 for June last, p. 202) used by him, and described its construction and action. 

 The principal working parts consisted of two cylinders, each covered by an 

 endless web, and so placed as to form the front and back of a hopper, the 

 two sides being iron plates, placed so that when it was filled with tempered 

 clay from the pug-mill, the lower part of the hopper, and consequently the 

 mass of clay within it, had exactly the dimensions of a brick; beneath the 

 hopper, an endless chain traversed simultaneously with the rotation of the 

 cylinders; the pallet boards were laid at given intervals upon the chain, and 

 being thus placed under the hopper and the clay brought down with a slight 

 pressure, a frame with a wire stretched across it, was projected through the 

 mass of clay, cutting off exactly the required thickness of the brick, which 

 was removed at the same moment by the forward movement of the endless 

 chain ; this operation was repeated each time that a pallet board came under 

 the hopper. Mr. Hunt stated that the chief object of the machine, which 

 was worked by hand, was to produce good square compact bricks, of uniform 

 quality, using only a slight pressure. He had found that it was very difficult 

 to dry bricks made by machinery where considerable pressure was employed; 

 because, before the evaporation from the centre of the clay was completed, 

 the surfaces were overdried and they frequently scaled off. These machines 

 were in operation in several parts of England, producing usually about 1200 

 bricks per hour, and er-.ch machine required two men and three boys to feed 

 it, turn it, and to take off the bricks ; the clot moulders were dispensed with, 

 and all the persons employed were common labourers; professed brick- 

 makers were thus not required ; he found this of much importance in the 

 contracts which he had taken for making bricks, both in this and in foreign 

 countries. 



The machine for making tiles (Journal for June, p. 202, Fig. 2) is on the 

 same principle as Fig. 1 ; it consists of two iron cylinders, round which webs 

 or bands of cloth revolve; by this means the clay is pressed into a slab of 

 uniform thickness, without adhering to the cylinders. It is then carried 

 over a covered wheel, curved on the rim, which gives the tile the necessary 

 form ; the tiles are polished and fiuished by passing through three iron 

 moulds of a horse-shoe form, shown in the centre of the cut ; the; are at 

 tiie same time moistened from a cistern placed above them. The tiles are 

 then cut off, to such leugths as may be required, and carried away by an 

 endless web, and are placed by boys on the drying shelves. Flat tile's, or 

 soles, are formed in nearly the same manner, being divided into two portions 



~ The average weight of Hunt's machine-made bricks is Gib. 7oz., and 

 of Con ley Stocks, 51b. joz. 



while passing through the moulds; the quantity of clay used for one draining 

 tile being the same as for two soles. In answer to questions from the Pre- 

 sident, he stated that the density of the bricks could be augmented, but in 

 that case, the time required for drying them must be increased, and fre- 

 quently artificial means were resorted to, which rendered them more expen- 

 sive. 



Captain Buller inquired whether any advantage was obtained by the pro- 

 duction of bricks of such a density as that exhibited by Mr. Prosser ; whe- 

 ther builders would not consider them objectionable from their great weight, 

 the difficulty of handling and cutting them, and the increased expense of 

 carriage. He had understood that the lightness of the London bricks, 

 which was chiefly owing to the ashes used in their composition, was con- 

 sidered an advantage, and that they were sufficiently strong for all building 

 purposes. 



Mr. Parkes was of opinion that the weight of Prosser's compressed bricks 

 would be objectionable for ordinary purposes, and he did not think that the 

 mortar generally used would adhere to such smooth surfaces as they pos- 

 sessed. The Roman bricks were very dense, but they were small in propor- 

 tion, and they were used with mortar or cement which had been carefully 

 prepared for a long period before it was used. The Dutch clinkers, which 

 were so very durable, were small in proportion with their density; and the 

 same might be observed of all foreign bricks, some of which were made 

 with great care ; for ordinary work he should prefer a brick of a less dense 

 quality than the compressed ones. 



Mr. Blashfield explained that Mr. Prosser's bricks could be rendered 

 lighter, by an admixture of ashes or other substances with the clay, if it was 

 considered desirable. 



Mr. Newton had recently examined a wall which had been built with very 

 dense bricks, and had twice fallen ; the bricks appeared to have absorbed the 

 moisture from the mortar, before it could adhere to their surfaces. He pro- 

 mised to exhibit on a future occasion, some bricks which were brought from 

 the pyramids of Egypt; they appeared to be composed of sand mixed with 

 chopped straw, and had not much cohesion ; yet they were strong enough 

 for the construction of such massive buildings as the pyramids. 



Mr. Hunt said that engineers generally preferred dense bricks as their 

 works required strength ; he had found it advantageous to use mild clay 

 instead of a stronger quality, as compact bricks made from the former, when 

 well-tempered, were better than those of the same density made from the 

 latter. 



Mr. Fowler said that the value of bricks depended upon their strength : 

 but he doubted whether density and strength were in this case synonymous; 

 and he thought that bricks of a cellular structure would not only be 

 stronger, but would unite better with the mortar. He thought, however, 

 that Mr. Hunt's machine would prove advantageous, as the bricks produced 

 by it would be of more uniform character than those made by hand mould- 

 ing. 



Mr. Pellatt believed that light bricks were generally porous, and that 

 when they were used for building external walls the moisture soon pene- 

 trated; this was not the case with dense bricks, and if they were generally 

 made more compact, thin walls would resist damp as well as thick ones. 



Mr. Cowper believed that for architectural purposes so much density was 

 not absolutely necessary. Houses three stories high had been constructed 

 by the mode of building called " Pica" work, which was merely ramming 

 down tempered clay into moulds of the thickness of the walls, and aliowing 

 the mass to be dried by the sun as the work proceeded. In countries where 

 the climate was very dry this method succeeded perfectly. 



Mr. Braithwaite understood that several kinds of brick were made for the 

 London market, that they were devoted to different uses and were sold at 

 various prices; some qualities were capable of supporting a great amount of 

 pressure, and were generally used with cement, while others were almost 

 rotten. 



Mr. Bennett said that the principal varieties of bricks were calied " malm 

 paviors," "stocks," "grizzles," "places," and "shuns"; for the first kind 

 the clay was washed and selected with care : the bricks so produced were of 

 superior quality. The other kinds were all made from the same clay merely 

 tempered, the difference between the sorts being produced entirely in burn- 

 ing them ; common stocks were good enough for all ordinary building pur- 

 poses ; but the inferior qualities could not be trusted for important works. 

 As to the relative prices of the several sorts, the difference between malm 

 paviors and stocks was 15s. or 20s. per 1000 ; between stocks and places 10s. ; 

 the grizzles obtained a price midway between the two last named, and the 

 shuffs were sold for an inferior price governed by their quality, as they were 

 frequently quite rotten. 



Mr. Lowe inquired what object there was in the mixture of " breeze " or 

 ashes, with the clay for making bricks; was it intended to render them less 

 dense, or to assist the combustion, when in the clamp or the kiln ? 



Mr. Bennett believed that the principal advantage of using a mixture of 

 ashes with the clay was, that it rendered the combustion more regular, when 

 the bricks were burned in open clamps; the sifted breeze was employed for 

 fuel instead of coal, which would otherwise be used for burning in close kilns. 



Mr. Hunt explained that the method of making bricks in the vicinity of 



