826 Mechanics, _Physics, and Ohemlstry.

ner, the second press being then in turn blocked by the water enclosed in it. The important feature in the invention is the blocking of one press, whilst a more powerful one is caused to act against it thus : ~ Two separate hydraulic presses, the one of small, and the other of large power, may be arranged one at each end of a frame, the material to be pressed between them is received between the two presses, and is partly compressed by the press of smaller power ; then this is blocked by enclosing water in it, and the press of greater power is put in ac- tion to complete the compression. This arrangement may also be em- ployed where mechanical blocking is used in place of or together with water blocking.

2Vew Manufacture of Gunpowder. From the London Artizan~ August~ 1862.

~Ir. W. Bennetts, of Tuckingmill, has invented a new method of manufacturing gunpowder, the ingredients consisting of lime, nitre, sulphur, and charcoal ; the lime is dissolved in a sufficient quantity of water to bring the other elements into a paste. The lime after having been made into a solution is strained through a fine sieve; this solu- tion is then added to the other ingredients, and the whole is put into a mill and ground until it becomes a paste ; it is then taken out of the mill and passed between two rollers, one grooved and the other plain. The paste by passing between the rollers is formed into long strips of a triangular shape; it is then carried on an endless web or canvass over some hot tubes, which are heated by steam, hot water, or any other artificial heat which may be applied ; by this means the strips are easily broken into grains. This mode of manufacture prevents a great deal of danger, as the powder is pulverized and brought into grain while in a wet state. The lime makes a firm grain, resists the damp, and gives it a degree of lightness which increases the bulk 25 per cent. over ordinary gunpowder--a great advantage for blasting purposes. Plaster of paris, blue lias, Roman or Portland cement,, or other strong cementing substance, may be used as a. s u ~ i t u t e for lime. And the patentee finds that for blasting purposes t~ fo l lowing proportions answer well--that is to say, nitre, 65 lbs.; Charcoal, 1~ lbs. ; sulphur, 10 lbs. ; and lime, 7 lbs.; but the proportions may be varied according to the strength required.

Safety- Valves of Steam Boilers. At a meeting of the Academy of Sciences of Vienna, M. de Burg

gave an account of his experiments on the mode of action of the safe- ty-valves of steam boilers. These results are in contradiction with the theoretical propositions upon which the regulations for the dimensions of these boilers have been based : inasmuch as in reality these valves do not rise to a height equal to one-fourth of their diameter, that is, one or more inches, but only so as to leave a passage for the steam whose diameter does not exceed the fraction of a line. These appara-