454 report — 1878. 



difficulty of ensuring perfect connection. As to the last, it often occurs that the 

 exciting solution makes its way upwards through the porous carbon and gradually 

 destroys the metallic connections, except when the cell has been very carefully 

 constructed. Inconveniences like this in a Leclanche electric bell battery induced 

 the author to substitute pieces of gas-pipe for the carbon, and this answered 

 admirably for months. The addition of a little hydrochloric acid occasionally to 

 the exciting solution of ammonium chloride being necessary. 



Double Jluid Bichromate Battery. — Ordinary sheet-lead is an effective sub- 

 stitute for carbon in this battery. Like all bichromate batteries, it is not constant, 

 requiring frequent renewal of the bichromate. The lead is practically unaffected. 



Platinised Lead, Single Fluid Bichromate, and Smee's Batteries. — Unprepared 

 lead is tolerably effective for the ordinary bichromate battery, but its power is 

 enormously increased when the surfaces are roughened, and thinly coated with 

 platinum. A single cell with plates about 3 inches by 4 inches will heat 4 inches 

 of platinum wire of about 20 gauge, and fuses the hair-like platinum wire used 

 sometimes to explode gunpowder. 



It is equally effective as a Smee battery. The results appear to be quite as 

 powerful. It answers capitally for working medical coils. The platinising is 

 readily effected by a process described by the author.* 



In conclusion, the author points out that large batteries can be thus constructed 

 very cheaply by any amateur, and that the size of the cell is almost unlimited, as 

 it is easy to get any sized sheet of lead ; while with carbon cells of large size the 

 plates require a multiplicity of connections. 



It is recommended to withdraw both plates from the exciting solution when 

 out of use. After being immersed some months, the platinum coating seems to 

 suffer a little, but can be easily renewed. 



Platinised lead has been recommended for Grove's battery by Callan,t but has, 

 I believe, never been tried in the forms I have mentioned. 



11. On a Neio Form of Electro-Registering Apparatus. By Denny Lane. 



In many forms of registering apparatus the friction of the tracing point upon the 

 paper is so great that it cannot be overcome by the motive force of the index of the 

 instrument to be registered. It is proposed to move the registering pencil by inde- 

 pendent mechanism actuating an arm which is always kept parallel with the index. 

 The index is placed between two small screws on the independent arm, the ends of 

 which are so placed as to be distant j^ of an inch from the index, while the latter 

 is exactly parallel with the registering arm. A voltaic current enters the index, 

 and so long as both arms are exactly parallel no current can pass to either screw. 

 If, however, the index moves j— of an inch, it touches one or other of the screws, 

 and the current is completed to one or other of two electro-magnets. This 

 electro-magnet attracts an armature which releases the detent of a fly train. 

 The train coming into action shifts the registering arm until it becomes again 

 parallel with the index, when the current ceases and the detent again holds the 

 train. By this mode the registering arm is always maintained parallel with the 

 index, and consequently the pencil which it carries registers the position of the 

 index ; but the motive power is derived from the springs or weights of the fly train. 

 The only work which the index has to do is to make contact with one or other of 

 the two screws. 



Instead of wheel trains, hydraulic or pneumatic apparatus may be employed to 

 raise or lower the registering arm, the operation of each 'being controlled by inlet 

 and outlet valves wrought by the armatures of electro-magnets. 



Unrike the photographic registrations, these can be seen at once, and the delay 



* The lead being cleaned with rough emery paper, and well roughened by a file, 

 is brushed over with bichloride of platinum. 



f Ann. Ch. Phys. (3) viii. 28 ; also Watts's Chem. Diet, ii. 426. 



