VOLTAIC INSTRUMENTS. 



of silicon in alcohol being introduced into the small tube by 

 Dr. Bird, a deposition of silicon upon the platinum was found 

 to take place in 24 hours, which was nearly black and granular 

 and is described as exhibiting a tendency to a crystalline form. 

 From an aqueous solution of the same fluoride, a deposition of 

 gelatinous silica was observed to take place around the reduced 

 silicon, mixed with which, or precipitated in a zone on the sides 

 of the tube, especially if of small diameter, frequently appear 

 minute crystalline grains of silica or quartz, of sufficient hard- 

 ness to scratch glass, and appearing translucent under the mi- 

 croscope. With a modification of the decomposing cell described, 

 Dr. Bird succeeded in decomposing a solution of chloride of 

 potassium, and obtained an amalgam of potassium. The inner 

 tube c, was replaced by a small glass funnel, the lower opening 

 of which was stopt with stucco, and which thus closed retained 

 a weak solution of the alkaline chloride poured into it. Every 

 thing external to this funnel remaining as usual, mercury con- 

 tained in a short glass tube, like a thimble, was placed in the 

 funnel, and covered by the liquid, and instead of the platinum 

 plate, a platinum wire coiled into a spiral at the extremity, was 

 plunged into the mercury, the other end of this wire being con- 

 nected with the zinc plate z, of the battery. The circuit having 

 been thus completed, the mercury had swollen in eight or ten 

 hours to double its former bulk, and when afterwards thrown 

 into distilled water, evolved hydrogen and produced an alkaline 

 solution. A solution of hydrochlorate of ammonia being sub- 

 stituted for that of chloride of potassium, in this- experiment, 

 the metal swells to 5 or 6 times its bulk in a few hours, and the 

 semifluid amalgam of ammonium is formed. These feeble cur- 

 rents thus effect decompositions, in the lapse of time, which 

 batteries of the ordinary form and considerable magnitude, may 

 effect very imperfectly, or fail entirely in producing. 



Volta-meter. The decomposing power of a battery is re- 

 presented by the quantity of oxygen and hydrogen gases evolved 

 in a cell of decomposition containing dilute sulphuric acid. 

 The volta-meter is simply a cell so charged, and of a proper 

 form to allow of the gases evolved being collected and mea- 

 sured. One of the simplest forms is that constructed for me 

 by Mr. Young. It is a stout eight ounce phial (Fig. 27), through 

 the cork of which two platinum wires are passed, with flat plates 



