ELECTEIOITY. 



243 



a small Siemens armature. The coils of this 

 electro-magnet are traversed by the current 

 produced by the rotating armature, after being, 

 by means of a commutator, made to flow in 

 one direction only. At the commencement of 

 rotation, the armature is acted upon merely by 

 the weak residuary magnetism of the electro- 

 magnet, and consequently only weak currents 

 are produced in its surrounding coil. These 

 weak currents, passing through the coils of the 

 electro-magnet in the same direction, instantly 

 increase the residuary magnetism, thereby 

 again producing increased induction currents 

 in the armature, and so on until the iron of the 

 electro-magnet has taken up the highest 

 amount of magnetism which it is capable of 

 holding. In this arrangement the coils are 

 short-circuited, and so kept during the revolu- 

 tions of the handle when current and magnet- 

 ism are developed to their utmost extent. By 

 now suddenly opening this short circuit a very 

 powerful current of short duration (expressly 

 adapted to blasting purposes) will pass through 

 a line connected to the terminals. The in- 

 strument is claimed to be handy, portable, 

 and useful in all weathers, having a superiority 

 over galvanic batteries and also over static- 

 electric machines, which only act in fine 

 weather. The instrument may be actuated 

 either by magnetism or by a current from a 

 single cell. After that there is always suffi- 

 cient residuary magnetism to induce a weak cur- 

 rent in the armature ; and thus a never-failing 

 supply of electricity is at command for the 

 object required. In blasting operations it is 

 said to work with great success. It is also 

 adapted for the release of clockwork or signal i 

 bells for railways, and for the sending of cur- 

 rents in rapid succession, into a line of tele- 

 graph. 



Electro-capillary Paper. M. Becquerel has 

 investigated certain electro-capillary phenome- 

 na, and describes the process and results as 

 follows: He prepared parchment-paper with 

 ordinary filter-paper by immersing in sulphuric 

 acid, containing fifteen per cent, of water, with- 

 drawing immediately and washing with a large 

 quantity of water. A tube closed by a dia- 

 phragm of this material, and filled with a 

 saturated solution . of nitrate of lime, was 

 plunged into a solution equally saturated with 

 sulphate of soda. Stalactites formed on the 

 under surface of the paper, composed of crys- 

 tallized double sulphate of soda and lime. 

 These stalactites are of variable diameter, 

 varying according to the size of the pores 

 which allow the passage of the nitrate of lime. 

 By diminishing the size of the capillary tubes, 

 the passage of the liquid is indefinitely re- 

 tarded, until it at length becomes inappre- 

 ciable. There is a point, in regard to the 

 diameter of these capillary tubes, where the 

 electro-capillary force ceases to act, and where 

 complete filtration ensues; a single pore is 

 sufficient to produce this effect. For this 

 reason it is necessary that the parchment 



paper be uniform. Some experiments were 

 made with siliceous diaphragms. Columns of 

 sand, varying from five millimetres to five 

 centimetres in height, kept in position in each 

 case by a tuft of asbestos, were substituted in 

 a former apparatus. In operating in Dutro- 

 chet's way, with solution of sugar, solution of 

 salt, and distilled water, simple filtration took 

 place, instead of a strong end osmose with the 

 organic membrane ; but this was not the case 

 when a saturated solution of sulphate of soda 

 was placed in the tube, and in the outer vessel 

 another of chloride of barium, an endosmose 

 of two centimetres resulting in two days. No 

 precipitate is seen in the outer vessel, so that 

 there is only a displacement of the solution. 

 In placing in a tube closed with a diaphragm 

 of parchment-paper a solution of sugar or of 

 salt, colored with litmus or other coloring 

 matter, and water in the outer vessel, a strong 

 endosmose is produced in the tube, and at the 

 end of a few days traces of color in the water 

 are only seen with difficulty ; the color is com- 

 pletely arrested by the membrane. 



An Improved Voltastat. Professor Guthrie 

 has exhibited to the British Chemical Society 

 an improved Voltastat by which the current 

 of a galvanic battery may be maintained per- 

 fectly constant and regular by a self-acting 

 arrangement, which is thus described : A ver- 

 tical glass cylinder of about the size of a test 

 tube is charged with dilute sulphuric acid, 

 with a layer of mercury below occupying 

 about one-third of its total contents. Partly 

 immersed in the acid liquid is a pair of 

 platinum electrodes insulated by glass fused 

 upon the wires at that portion which passes 

 through the cork stopper of the jar, and a 

 comparatively wide glass tube open at both 

 ends is fixed in the same cork, with its lower 

 extremity dipping below the level of the mer- 

 cury, while another delivery tube with -bulb 

 and capillary orifice provides for the slow es- 

 cape of the mixed gases resulting from the 

 electro-decomposition of the water. This ap- 

 paratus having been placed in the battery cir- 

 cuit, say of three Bunsen cells, evolves the 

 oxyhydrogen gas with a rapidity which may 

 be easily regulated by the size of the aperture ; 

 if, then, the activity of the battery is increased, 

 the larger volume of gas, unable to escape, 

 exerts a greater degree of pressure upon the 

 liquid contents of the cylinder, and the mer- 

 cury is forced up the open tube, whereby the 

 column of liquid descends and smaller surfaces 

 of the platinum plates are left immersed, and 

 the power of conduction is to a corresponding 

 extent lessened. In this manner the author 

 states that he found no difficulty in maintain- 

 ing a perfectly uniform current for a period 

 of six or seven hours, and any required adjust- 

 ment could be majle by altering the size either 

 of the apparatus or of its component parts. 

 By collecting the gases evolved, this little ar- 

 rangement could also be made to serve as a 

 voltameter. The president of the society, Mr. 



