MECHANICAL AND USEFUL ARTS. 67 



And it is a singular fact in relation to the diameters of the new 

 coins, which are respectively : — 



Pence 1'200 inches. 



Halfpence 1000 „ 



Farthings -800 „ 



that as twelve halfpence give an exact measurement of one foot, so 

 do four pence, four halfpence, and four farthings placed edge to 

 edge, on a flat surface in single file, give the same result. 



As the halfpenny is exactly one inch in diameter, like the Cana- 

 dian decimal cent, it may be used, if need be, in lieu of the car- 

 penter's rule. As, for example, 12 halfpence = one foot, and 3S 

 halfpence = one yard. 



PATENT ENAMEL SURFACING FOR METAL PIPES, &C. 



It has long been noted that ordinary earthenware is not adapted 

 to stand the varied temperature of the oven. It was with the idea, 

 in the first place, of obviating this difficulty that it suggested itself 

 to Mr. Paris to manufacture dishes and basins of sheet iron or 

 other metals, and cover them with a Coating of Enamel, making 

 them, in fact, china with a metallic core ; thus causing them to be 

 free from the destroying properties of oxidization, and at the same 

 time be durable and not liable to break when heated to any mode- 

 rate temperature. This peculiar manufacture has now become an 

 important feature in the Birmingham hardware trade ; it has been 

 already pretty well brought to perfection, and the manufacture of 

 enamelled pie-dishes, wash-hand and other basins, candlesticks, and 

 other articles is very extensive. 



Some slight idea may be conceived of the increasing demand for this 

 kind of article, from the fact that during the last year 60,000 pie- 

 dishes were turned out at Salt's patent enamel works. But the 

 most important use to which this enamelling process has yet been 

 applied, is for securing both the internal and external surfaces of 

 iron pipes from the corroding action of fluids. This improvement is 

 well worthy of the attention of hydraulic engineers, for it has been 

 found, in practice, where pipes so prepared have been laid down, 

 that the water delivered has retained its original purity, nor does it 

 even deteriorate by long standing ; added to this, the pipes them- 

 selves are found to last three or four times as long as they otherwise 

 would, so that the extra outlay is soon compensated for. The pro- 

 cess of enamelling miscellaneous articles is simply as follows : — 

 Having been stamped out in a most ingenious manner by machinery 

 prepared for that purpose, they are in the first place immersed in a 

 pickling bath for the purpose of freeing their surfaces of extraneous 

 matter ; they are then placed for a short time in a sulphuretted fur- 

 nace, and, thus prepared, are brushed over with a thick coating of 

 pounded glass, &c. The articles are then placed in a furnace heated 

 to a temperature of between 2000° and 3000°, which causes a lique- 

 faction of the silicious covering, and then a combination of the 

 enamel and iron takes places. This is so perfectly effected that if 

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