98 ANNUAL OF SCIENTIFIC DISCOVERY. 



sheet of rubber are roughened in its manufacture, by placing it between 

 two coarse cloths and then passing it through calender or spreading rollers 

 between the coarse cloths after it leaves the rollers ; or by passing the sheet, 

 before it becomes hard or set, between the surfaces of two rough rollers or 

 any other surfaces suitable to produce a roughness or a series of minute cavi- 

 ties all over both surfaces of the sheet. It is next vulcanized, and afterwards 

 boiled in a solution of potash to remove the sulphur which is precipitated on 

 the surface after vulcanization, and which would prevent adhesion. After 

 this the cement is spread over both surfaces of the rubber, and the cloth is 

 applied in the usual way, while the rubber is kept at such a tension as is 

 necessary to give the goods the degree of elasticity required, and the whole is 

 passed between rollers which have plain smooth surfaces. Plain smooth rol- 

 lers are the best for this purpose, as they insure better adhesion of all parts of 

 the surface of the rubber and cloth ; but a rib or figure may, if desired, be 

 produced on the surface of the goods by grooving, embossing, engraving, 

 indenting, or otherwise ornamenting the periphery of one of the rollers and 

 covering the other roller with felt or some yielding substance. This rolh'ng 

 operation completes the process. 



PEEFOEATED OE SOLID BEICKS. 



Some experiments have lately been instituted at Belfast, Ireland, on the 

 comparative sustaining power of patent perforated bricks and bricks of 

 the ordinary kind. In each case a pier of four courses of the bricks to be 

 tested was built, hi Roman cement, on the table of a powerful hydraulic press, 

 and allowed at least 24 hours thoroughly to set. A light scale board was 

 suspended to the safety-valve lever of the press, on which there were placed 

 successive weights, until the pier of bricks on the table of the press was 

 crushed. The number of weights was increased a quarter of a pound at a 

 time (being an equivalent to an increment of 10 tons on the press), com- 

 mencing at 30 tons, this starting point being the effect due to the united 

 weights of the level and scale board. The pump was worked very slowly, to 

 eliminate the concussion produced otherwise by the inertia of the water. The 

 first experiment was made with good ordinary brick, in a pier of 18 in. square, 

 built in four courses. This showed symptoms of failing with 110 tons, and 

 was crushed with 150 tons. A pier of the same dimensions of perforated 

 bricks began to crack with 270 tons, and was crushed with 350 tons. Sir 

 John M'Neil having expressed a desire to witness a repetition of these expe- 

 riments, at his request a pier of 9 in. square of each kind of bricks was built 

 in cement, in four courses as before, and with especial care to have the joints 

 as thin as possible. The common bricks failed with 40 tons, whereas the 

 pier of patent bricks sustained 120 tons before it was crushed. Reducing the 

 result of these experiments to the effect upon a superficial foot, common 

 bricks, in the first experiment, were crushed by 66| tons to the square foot, 

 and by 71 1 tons to the second, the mean being 68f tons. Patent perforated 

 bricks were crushed in the first experiment by 1551 tons per superficial foot, 

 and in the second by 213 tons, the mean being 184| tons. 



A paper on the manufacture of bricks was recently read before the English 



