Processes in the Useful Arts. 347 



the trowel to a smooth surface. When dry, its surface may be made per- 

 fectly smooth and shining with pulverised Venetian talc. 



When the cement is to be applied to buildings, the rough ground for 

 receiving it should be prepared as follows. Mix together equal parts of 

 the coarsest river sand, and the sand which is pulverised from millstones, 

 and add a third part of lime which has been slacked for about three months. 

 These are then to be made into a paste with water, and when it is about 

 to be used, add a fifth part of very fine sifted lime, and apply it as a com- 

 mon plaster. — See Newton's Journal of the Arts, July 1826, p. 372. 



9. Mr Samuel Morey's New Vapour Engine. 



Mr Morey has taken out an American patent for this invention. The 

 vacuum in the cylinder is produced by firing an explosive mixture of at- 

 mospheric air, and the vapour of common proof of spirits mixed with a 

 small portion of spirits of turpentine. A working model has been set in 

 motion and kept at work without raising the temperature of the fluid which 

 yields the vapour, higher than that of blood heat. — Franklin's Journal. 



10. Account of the Performance of one of Mr Perkins's Steam-Engines. 



The following very interesting observations on Mr Perkins's steam en- 

 gine are taken from the last number of Mr Newton's Journal of Arts. 



Mr Perkins's system of generating high steam has recently been ap- 

 plied to the Cornish single stroke pumping engine by Mr Samuel Moyle, 

 civil engineer, from Cornwall. Although the engine is not yet complete 

 in all its parts, yet enough has been done to prove its great power and safety. 

 As to the economy of the fuel, although undoubtedly great, nothing deci- 

 sive is yet known, owing to the imperfection of the injecting pump, which 

 occasionally failed in giving the full supply of water, upon which the proper 

 supply of steam wholly depends. Enough, however, has been done to 

 establish the important fact, that the higher the steam is used the greater 

 is the gain. Steam used at forty-two pounds per inch, or at three atmo- 

 sphere's pressure, without condensation in the cylinder, is undoubtedly not 

 likely to do more, if so much, as the condensing engine using steam at 

 three or four pounds per inch pressure. The eduction side of the piston 

 has not only to overcome the pressure of the atmosphere, but the friction 

 of the steam rushing from the cylinder through the eduction pipe, which 

 will amount to at least half an atmosphere more, making twenty-one pounds 

 resistance: add the friction of the piston, piston-rod, and valves, then 

 there will be very little more pressure, if any, on the inch than when low 

 condensed steam is used. It would appear, that about two-thirds of the 

 forty-two pounds pressure on the inch is lost by the resistance on the 

 eduction side of the piston. But as you increase the pressure of the steam 

 tin- gain is almost wholly on the induction side of the piston, since the re- 

 sistance to the escape of the steam is very little more, whether you woik 

 with 500 pounds per inch or forty-two pounds per inch. 



The following statements will show the power and safety, although not 

 the amount of the saving of fuel. This engine, with a nine anil one- 



