Rensselaer Republican, Volume 17, Number 27, Rensselaer, Jasper County, 12 March 1885 — MECHANICAL. [ARTICLE]

MECHANICAL.

There is but one place in the United States where gun cotton is made. Until six months ago the Navy was obliged tod* pend upon England for all gun cotton used, but a manufactory has been erected at the torpedo station. Newport, which now produces all that is required for sea-going men-of-war and torpedoes.

The superiority of American dredging machines, which has been Bhown in the work on the Panama Canal, has led to orders for them by foreign governments. The last of these is from Spain. A drag boat with; 7 a screw propeller of 100-horse power, five iron barges and two towboats h-ve been called for to be nsed at the port of San Juan, Porto Rico. Although jute has now assumed such. importance as an article of commerce, the first at empts to utilize its fibre were not made in Europe until 1834-5, and it was only when the Crimean War deprived England of Russian flax and hemp that jute fibre became highly valued. The centre of trade in Great Britain is Dundee. Of late years Germany has gone largely into it. • Sawdust is mixed with common alluvial clay, now, • and the compost is ground and pres ed by machinory, and baked like bricks. The result is called terracotta lumber, which is spongy enough, the sawdust having been burned out, to admit of the nseof wood-working tools upon it. It is only adapted for inside work, and is used like brick, each piece being about a foot long, six inches wide, and four inches thick. The surface is and can be finished by two thin coats of plaster. It is lighter than a similar wall of studding and lath, heavily plastered. It holds a nail well, and it affords, it is claimed, a prime system of fireproofing. The tronble which Philadelphia is having with the masonry of her new city hall is similar to that experienced with the capitol building in Hartford a few years ago. When the latter edifice was completed, large chips began to fall from the faces of granite blocks in the dome piers, sadly marring those massive supports, and exciting grave fears about the security of the whole fabric. Further settling, however, was prevented by ben ing into the piers and filling the interstices with several tons of molten type metal. And the granite was so dexterously patched and veneered that only 'upon careful inspection oould one find traces of the damage wrought by the unevenly distributed pressure.

A valuable enamel for artistic purposes, says a Dresden journal, may be prepared from a mixture of thirty parts, by weight, of saltpetre, ninety Darts of silicic acid and 250 parts of litharge. Drawings can be made upod this enamel as upon paper, and the characters can be burnt in by means of a muffle in Iss than a minute. It can also be employed .n the preparation of photographs without the use of collodion. For this purpose a mixture of ten parts of gum, one of honey, and three of bichromate of 1 potash, well filtered, is dried upon the enamel and exposed in the camera, the image being then developed by dusting tver it a powder of ten parts, by weight, oxide of cabalt, ninety of pulverized iron scales, 100 of red lead and thirty of sand; the chromate is decomposed by immersion in a slightly acidulated bath. When washed and dried the enamel is melted by packing it upon a piece of clean sheet iron, and coated with chalk, and the photograph glazed upon the enamel is then brought to view.