MECHANICS AND USEFUL ARTS. 115 



powder was discovered by the chiemist Norrbin." The German 

 •* Building News " contains extracts from a report of the Prussian 

 architcLt, Steenke, who makes the following remarks upon the 

 safety of ammonia powder : "Experiments were made by fas- 

 tening a lamp to a pendulum, which was caused to oscillate ; 

 gunpowder, gun-cotton, nitro-glycerine, and dynamite all took fire 

 as the flame passed over them, but the ammonia powder did not 

 begin to burn till it had been touched by the flame 20 times. In 

 making experiments upon the force of the blow required to ex- 

 plode it, it was found that, with the apparatus employed, where 

 the fall of a weight from 4 feet to 5 feet would explode gunpow- 

 der, nitro-glycerine only required 1^ feet to 2 feet, dynamite 2| 

 feet to 3 feet fall, whilst a fall of from 12 feet to 15 feet was 

 necessary to cause the explosion of the ammonia powder. 



PROCESS FOR THE PRESERVATION OF THE BOTTOM OF IRON 



SHIPS. 



A writer in the Comptes Rendus of July 26, 1869, says : — 

 '♦ The iron actually employed in maritime construction is 

 nearly always of an inferior quality, and presents a very great 

 heterogeneity. From that cause foci of electric action exist which, 

 provoking the decomposition of water or saline matter that it con- 

 tains, lead to a prompt deterioration of the shell ; the points at- 

 tacked are then the parts left vacant by clusters of mollusks and 

 weeds which clog the passage of the ship. The problem pro- 

 posed to us, and which we believe to have solved, is to prevent this 

 oxidation, the first cause of the clusters. In our system the ship 

 is transformed to a kind of a vast pile of buckets ; reservoirs in zinc 

 are placed, under the form of tubes or boxes, on the interior sides. 

 These tubes, in perfect communication with the iron of the ship, 

 instead of bolts, rivets, or other instruments, are filled with sea- 

 water that is renewed every day. Plates of zinc between win- 

 dows circulate in the interior of the ship, and hoop the different 

 parts with the tubes or reservoirs. In the course of oxidation, 

 the zinc charges itself with negative fluid, which it transmits by 

 electricity to the iron ; the shell becomes then like an immense 

 electrode char<>:ed with this fluid. We thought at first that the 

 iron, recovered, so to speak, with an envelope of negative fluid, 

 ought to take, by this means, a certain electric polarity, and thus 

 avoid the action of the electro-negative bodies contained in the air 

 or the ocean ; the negative fluid ought to flow out in a continuous 

 manner into the water, and the positive fluid of the liquid to dis- 

 sipate little by little into the humid air, and thus independently 

 of the particular currents establish themselves in the interior of 

 the boxes between the liquid and the iron bolts which fasten the 

 reservoirs to the ship. Whether the electric communication was 

 imperfect, whether the flow of the positive fluid into the air was 

 insuflicient, the carrier-boats of this kind of preparation have 

 presented only a half success ; thus the interior has been well 



