102 
POPULAli SCIENCE REVIEW. 
disappear the bath was filtered and gave clean pictures. The second was a 
bath which had been used with Harnecker’s collodion, and was choked up 
with organic matter producing fog. With this bath, four or five times as 
much permanganate was required as the other. When enough had been 
added the bath was filtered, and, at Jirst, gave clear pictures, but, after 
standing a little, fogged. On being acidulated with dilute nitric acid it 
worked perfectly. The explanation of this last lies in the tendency of the 
permanganate to render a bath alkaline ; therefore the proper mode of treat- 
ment is, if much permanganate has been added, to acidulate the bath. If 
but little has been needed the bath may be tried, and no acid need be added 
unless a tendency to veil show itself.” — See “ Spirit of the American Jour- 
nals ” in British Journal of Photography, Dec. 18. 
PHYSICS. 
A Neio Constant Battery . — This battery, intended rather as an intensity ” 
than a quantity ” battery, has been devised by Messrs. De la Rue and 
Muller. Having experimented with it since its construction was first made 
known in February, and more especially tested its electro-motive force, the 
inventors have recently given a detailed account of it to the Chemical So- 
ciety. The battery is compact and always ready for use j no porous cell is 
needed, and, witli the electrodes disconnected, the elements may be left im- 
mersed for several weeks, as the electro-positive metal is then scarcely acted 
on in consequence of the electrolyte being solid and very nearly insoluble. 
The positive metal is, as usual, zinc. It consists of Belgian zinc wire 
(English being objectionable from its impurity) 2f inches long and 0 2 inch 
thick. The negative element is pure silver in the form of wire 0-03 inch 
thick ; and round this is cast the electrolyte, a cylinder of chloride of silver 
0*22 inch in diameter. The silver wire projects about 0*2 inch beyond the 
bottom end of the chloride of silver, and about 1 ^ inch above the top of it, 
so as to permit of its connection with the zinc of the next pair of elements. 
The cells are conveniently formed out of 1-ounce vials by cutting off the 
necks with a diamond or an ignited splint coal. The zinc and chloride of 
silver rods pass through, and are supported by a lath of varnished mahogany. 
The ends are pierced by two holes large enough to allow of it sliding freely 
up and do\Mi two vertical supporting rods of glass. Upon these glass sup- 
ports it is retained at any desired height by vulcanised caoutchouc collars ; 
tliese grip the glass rods with adequate iirmncss to support the mahogany 
bar, but at the same time permit of its being moved up and down with 
sufficient freedom to immerse tlie elements partially or wholly or to raise 
them entirely out of tlie liquid. Tlie raising is conveniently performed by 
placing the two forefingers ofeacli liand under the collars and pressing the 
thumbs on tlie top of tlie glass rods ; the lowering can be efiected by pressing 
down the two ends of the bar. The glass rods should not be vaniished on 
that portion over which the vulcanised collars have to slide, as the varnish 
causes too much friction ; below this point they may be varnished with ad- 
vantage. They are cemented into a base of varnished mahogany, in which 
