Progress of Invention. 75 



is no trigger, and therefore it is impossible that the gun can go off 

 by accident. The needle which ignites the explosive compound in 

 front of the powder, passes into the screw which forms the breech, 

 being kept back in its normal position by a spiral spring: it 

 abuts against a thin elastic plate that closes the aperture in the 

 screw, and does not project beyond the general surface. When the 

 gun is to be discharged, the thumb of the right hand is pressed on 

 the elastic plate. This forces in the needle, and ignites the deto- 

 nating compound. 



Improvements in Galvanic Batteries. — If the nitric acid in the 

 Bunsen battery is replaced by an aqueous solution of picric acid, 

 the evolution of disagreeable and unwholesome gases will be pre- 

 vented, while the efficiency of the battery will not be injuriously 

 impaired. The dilute sulphuric acid may be replaced by a solution 

 of sea salt. The addition of picric acid also to a battery containing 

 but one fluid greatly improves its action. The resistance to the 

 current caused by the porous vessel of a Daniels battery is removed 

 by a slight modification of its details. Within the outer vessel, 

 which may be made of glass or porcelain, is placed a cylinder of cop- 

 per much smaller than the outer vessel, but having attached to 

 its lower end a disc of copper that just fits on the bottom of the 

 outer vessel. Between the latter and the copper cylinder is the 

 diaphragm, a cylinder of glass or ordinary porcelain, having on the 

 outside, at the distance of one-third of its height from its lower 

 extremity, small projections for supporting a cylinder of zinc. This 

 battery is charged by placing siliceous sand in the interior of the 

 diaphragm, and on this sand crystals of sulphate of copper ; then 

 pouring a solution containing about five per cent, sulphuric acid 

 gradually into the outer vessel, until it reaches the crystals of sul- 

 phate. The electricity passes directly from the zinc to the copper 

 disc, without being retarded bypassing through a porous vessel. If 

 the exterior vessel is glass, any deposit of copper on the zinc can be 

 perceived at once and prevented. The greater the number of times 

 per day the battery is to be used, the more permeable ought to be 

 the sand, that the sulphate may be supplied with sufficient rapidity. 

 The stratum of dissolved sulphate must never be allowed to rise 

 high enough to come in contact with the zinc ; if it is becoming too 

 high, sand is to be added, or some of the liquid within the diaphragm 

 is to be removed with a syphon — which will cause the sulphate to 

 be driven back, on account of the greater height of the liquid in the 

 external vessel. 



Improvements in Plating and Gilding. — The danger to the 

 workman from contact with mercury is entirely prevented in gilding 

 and plating, by dipping the article to be gilt or plated in the solu- 

 tion of a basic salt of mercury while in connection with the positive 

 pole of a galvanic battery, and, when it is covered with mercury, 

 immersing it in a strong solution of the gold or silver salt ; then 

 plunging it a second time in the mercurial solution, and afterwards 

 evaporating the mercury in a furnace. Or the article which is to be 

 gilt may be dipped into sodium amalgam, the surface of which has 

 been covered with a little water, the portions which are not to be 



