MECHANICS AND USEFUL ARTS. 99 



web, which carries it away. The presses act simultaneously, and 

 between every stroke the table makes one-third of a revolution, by 

 which the coal is removed from one press to the other. An appara- 

 tus is provided for extracting the gases from the coal during pressure, 

 ingeniously opening out the air-passages at each stroke, which would 

 otherwise become choked by the bitumen. In these presses, necessa- 

 rily of a very powerful description, breakages would be always occur- 

 ring but for a provision which has been made, by the fulcrum of the 

 levers of the main press resting on the ram of a hydraulic press, the 

 safety-valve of which is loaded only to the extent that the strength 

 of the machine will bear. Each machine, which is inexpensive in 

 construction, is capable, it is calculated, of making twenty-eight tons 

 per day, at an estimated cost of two shillings per ton. From having, 

 during the process of washing, the stony parts removed, and from the 

 lighter gases which produce smoke being driven off during the man- 

 ufacture, it is said that steam vessels provided with these blocks of 

 compressed coal will carry fuel for steaming nearly double the num- 

 ber of days ; and, moreover, that this fuel is free from the danger of 

 spontaneous combustion. 



COMPRESSED BREAD. 



To replace the indigestible hard biscuit used in the French army 

 and navy, a preparation of compressed bread has been recently intro- 

 duced. Small loaves baked in tins are thoroughly dried and then 

 pressed into cakes (four inches square and three-quarters of an inch 

 thick) by a machine invented and patented by M. Marinoni, of Paris. 

 The cakes recover their original dimensions when put into water. 



ORNAMENTAL BURNT WOOD-WORK. 



The following mode of producing ornamental wood-work by burn- 

 ing is now practised in London. Designs in relief are engraved on 

 the face of hollow iron cylinders ; and these, being heated by a gas- 

 pipe within, acted on by a second pipe conveying atmospheric air, 

 are made to transfer these designs to the planed board which is passed 

 in between them as they revolve. When the wood has gone through 

 the charring operation, it is handed to a workman, who scrapes it 

 down over the surface so as to bring out the lights and produce the 

 best effects. This being accomplished, the face is varnished or pol- 

 ished, and the result is an ornamental panel or moulding of consider- 

 able beauty (if the design be good), and of remarkable permanence. 

 White woods, as sycamore or lune, are employed for the work. It is 

 easy, also, by this process, to give to the less expensive varieties of 

 wood the characteristic of the more costly kinds. Rosewood and wal- 

 nut are very well imitated, and upon these any pattern can be im- 

 pressed. The cost of woods imitated in this way is put at two-thirds 

 the cost of good hand "graining." 



IMPROVED BOLT. 



Messrs. Lawrence and White, of Melrose, N. Y., have recently 

 patented an improved bolt, which has all the excellency of the rivet, 



