Nov. 30, 188"?.] 



♦ KNO^AALEDGE • 



333 



The evidence now obtained confirms the theory which 

 was advanced in 1848 and has since been maintained by 

 Gosse and others, that a race of marine animal exists, in- 

 cluding probably several varieties, which is characterised 

 by a serpentine neck, a head small compared with the 

 body, but lar^e compared with the thickness of the neck, 

 an air-breather, and deriving its propulsive power from 

 paddles — in other words, a modern representative of the 

 long-necked plesiosaurians of the great secondary or 

 mesozoic ei'a. Creatures of this class have beeu aptly 

 compared to what would be formed by drawing a serpent 

 through the body of a sea-turtle. — Newcastle Weekly 

 Chronicle. 



THE AMATEUR ELECTRICIAN. 



BATTERIES VI. 



AN inexpensive, but at the same time efficient, form of 

 bichromate battery may be constructed with but 

 very little trouble. When a comparatively powerful cur- 

 rent is required, it is generally speaking more advantageous 

 to use a number of small plates, in preference to a pair of 

 Jarge ones. In Fig. 1 is illustrated a combination of five 



plates — two of zinc and three of carbon. The same general 

 arrangement will do for any number of plates, providing 

 that the number of carbons always exceeds that of the zincs 

 by one. Six inches liy three inches will be found a very 

 convenient sizcf for the plates, the zincs being a quarter of 

 an inch thick. The thickness of the carbons is not very 

 material, except for convenience' sake. They are, however, 

 usually sold about a quarter of an inch thick. In titting- 

 up, tlio zincs and carl ions should alternate, as shown in 

 Fig. 1 (CZCZC), and sliould be separated at the bottom by 

 strips of wood (WW) about three inches long and a quarter 

 of an inch in section. The carbon plates should previously be 

 capped by bending over th(^ top of each carbon a strip of thin 

 sheet lead. 1'he lead answers the double purpose of keep- 

 ing the solution fror.i the upper portions of tlie cell, and of 



insuring good metallic connection. A small brass terminal 

 or binding screw (A) should also be soldered or screwed on 

 to one of the zinc plates (Z'), and should embrace also the 

 free end of a piece of copper wire, soldered (as at D) to 

 the other zinc plate (Z").' A stout brass clamp or binding 

 screw ( B) holds the arrangement together at the top, and 

 connects the external carbons (C and C"). The lower 

 portions being kept in position by means of a stout india- 

 rubber band (not shown in the diagram), a piece of copper 

 wire, or a strip of thin sheet copper clamped at one end 

 between the lead cap of the centre carbon (C") and a con- 

 tiguous wooden rod (W), and at the other end between the 

 terminal (B) and the lead cap of the external carbon (0^^') 

 places C'l in electrical connection with the other carbon 

 plates. A and B afibrd the requisite facilities for con- 

 necting the battery to the circuit through which the 

 current is designed to travel. The series of plates may be 

 placed in an earthenware or other non-porous vessel of 

 suitable dimensions, say four inches in diameter and five 

 and a-half inches deep. 



For the solution, dissolve bichromate of potash in boiling 

 water until the solution becomes a saturated one, and add 

 to it about one-tenth the volume of sulphuric acid. 



As the solution is a highly corrosive one, it is advisable 

 to coat all exposed metallic surface with pitch, sealing-wax 

 varnish,* or some other unassailable substance. 



The plates should only be kept in the solution when a 

 current is required, and some device for accomplishing this 

 is necessary. With expensive forms, such as the bottle 

 bichromate (see Knowledge, No. 10.5), this object is 

 attained by supporting the zinc plates at the end of a long 

 brass rod, which slides tightly in a vertical tube, a small 

 nut being used to keep the rod in any desired positicn. 

 The carbons in this case remain in the solution. Where 

 there are several cells in use they are placed in a kind of 

 box, and all the plates are attached to a rod which is raised 

 by means of a strong cord controlled by a winding arrange- 

 ment. An equally "efficient device is to stand the cells on 

 a board, carrying at each extremity an upright about twice 

 the height of the cell, one of them being so shaped as to 

 allow a rod, to which the plates are attached, to be lifted 

 and lodged in grooves cut in the upper end of each upright. 

 With a single cell, however, the best and cheapest plan is 

 to use a second glazed earthenware jar, and after washing 

 the plates (without taking the arrangement to pieces), place 

 them in it, and let them remain there till the cell is again 

 requii-ed. 



Double liquid bichromate cells are very numerous in 

 form and constitution. The simplest is that in which a 

 bichromate of potash solution replaces the nitric acid in 

 the Bunsen cell. It is found to give good results, and we 

 have used them at various times during the past ten or 

 twelve years with great success. The cell yields a current 

 almost equal to the Pjunsen ; it is more durable, more con- 

 stant, more economical, and gives off a mucli smaller 

 quantity of fumes, which are also of a less obnoxious 

 nature. As a result of considerable experience, it is 

 found that the depolarisation of the negative plate, or, in 



* An extremely handy mixture, which may be prepared by dis- 

 solving good shelllao in methylated spirit, nntil the solntion is of 

 a consistency suitalile for the particular purpose for which it may 

 be made, and then adding a very small quantity of vermilion, 

 sufficient only to give the (tesired tint. It is better to prepare the 

 solution in this way than to use manufactured sealing-wax, which 

 generally contains foreign ingredients of an injurious nature. 

 The varnish must not bo too thick, otherwise it will take an 

 unnecessarily long time in drying. If too thin, there is a wasteful 

 consumption of spirit. Experience will best indicate the most ad- 

 vantageous consistency. The varnish may be kept for along time 

 if well bottled. 



