114 
MESSRS. W. DE LA RUE AND H. W. MULLER ON THE 
(this is now obviated by placing six discs of vegetable parchment on the chloride), the 
total weight of silver contained in the charge was — 
600 X 14'5 X 15 '4325 X 3 
480X4 
= 20978 troy ounces of silver. 
The quantity recovered was 20 6 '9 2 
Loss 2 ’8 6 or 1*38 per cent. 
Working in a large way this percentage, though small, would be still diminished, 
so that the chloride of silver battery is not costly in its working ; and we venture to 
believe that it is destined yet to find a place in telegraphy, for which its great 
constancy, and the very little attention it requires, particularly suit it. It is without 
question a valuable implement for scientific research, and a source of great comfort to 
the operator, who finds it always ready at hand whenever he enters the laboratory. 
Both the iodide and bromide batteries appear to form a much larger quantity of an 
oxyhaloid compound than the chloride ; the iodide solution especially seems to act on 
the zinc rods, causing filaments of metal to form, and bridge across towards the iodide of 
silver element. They may be useful in making up in combination with chloride cells a 
battery of an exact number of volts, thus — 
volts. 
3 cells chloride = 3 X 1'03 = 3'09 
1 cell bromide 0*908 
3-998 
Average per cell 0 - 9995 
The Discharge in Air at Pressures less than the Ordinary Atmospheric Pressure. 
Only a few experiments have as yet been made by us on the length of spark at 
different pressures below that of the atmosphere, but we intend to pursue this 
investigation with a micrometer discharger of longer range than that shown in fig. 1, 
page 58. The following results were obtained with our present means with a point 
and a disc and 8040 cells : — 
Pressure. 
Fraction of an 
Length of spark. Ratio to length at 
Ratio of length of spark 
millims. 
atmosphere. 
inch. 
1 atmosphere. 
to dilatation. 
760 
\ 
0-34 
1 
i = 1-0000 
326-82 
2*3 2 6 
0-68 
2 
nnnr = 0-8598 
229T7 
3*3 1 6 
1-02 
3 
Irhi = 0-9046 
197-29 
3 * 8 5 2 
1-19 (limit) 
3-5 
3 = 0-9086 
so that with a point and a disc the length of spark is not precisely in the inverse 
ratio of the pressure. 
