Processes in the Useful Arts. 843 



When the wheel is mounted on a horizontal axis, the workman gives it 

 a motion of rotation with a spring-bow, and holds the stone which he cuts 

 in his left hand, applying, occasionally, corundum powder and water. 

 The polishing is effected by leaden wheels, and a finer powder. M. De 

 La Tour, Mem. du Museum, torn. ii. p. 230- 



6'- Dr Church's New Boring Auger. 

 This patent auger, of which the specification is not yet enrolled, is the 

 invention of Dr Church of Birmingham. One of these instruments, which 

 has been tried by Mr Newton, a competent judge of its merits, is one 

 inch and one-eighth in diameter. When turned like a gimblet by the 

 right hand, it passed through a four inch dry deal, four inches thick, in 

 fifty seconds. With the assistance of a bow, it penetrated a post seven in- 

 ches square, in twenty-one seconds. It cuts a perfectly smooth hole, and 

 clears itself as it advances. It can be sharpened upon an ordinary grind- 

 stone, and will retain the same form and properties though ground down 

 within a short distance of the stem. Newton's Journal of the Arts, vol- ix. 

 p. 91. 



7- Evans's New Method of Roasting Coffee. 



This process, for which a patent has been taken out by Mr R. Evans of 

 London, consists in preventing any of the oily parts of the coffee which 

 contain the aroma, from evaporating during the process of roasting it. The 

 machine consists of a cylindrical vessel turned by a winch and two wheels. 

 It has ledges within to throw the beans from the side to the middle of the 

 cylinder. At the middle of the cylinder, opposite to the handle, a tube 

 passes from the open air to beyond its centre, having a great number of per- 

 forations in it. During the first period of the roasting, the aqueous parts, 

 which the heat drives off, pass through the holes of this tube j but, when all 

 the water is driven off, this tube is shut up, and, consequently, during the 

 last period of the roasting, the aromatic oil does not escape from the beans. 



In order to ascertain the precise time when the aqueous vapours are 

 dispelled, he holds a piece of Blate against the outer end of the tube with 

 perforations, and the deposition upon its surface, if watery or gummy, 

 shows whether the water or the oil is escaping. Small quantities of 

 the beans are occasionally taken out with a spoon through the axle, to ob- 

 serve the progress of the operation. An abstract of the specification is pub- 

 lished in Newton's Journal of the Arts, vol. ix. p. 72. 



8. Braconnot's Process for making Blacking for Leather. 

 M. Braconnot has published, in the Annates de Chimie, Sfc f , for Novem- 

 ber 1824, p. 333, the following process for making a superior and cheap 

 blacking for leather of all kinds. Take 



Plaster of Paris passed through a fine sieve of silk, - 100 parts- 



Lamp black, ----- « 25 



Malt used by brewers, - - - - - 50 



Olive oil, -----. a 



