Thursday, August 22, 2013

Before The Dry Cell

Early radio equipment was all battery-powered. There were a handful of devices that were powered by crank dynamos, but for all practical purposes by the time we were using the word "radio" instead of "wireless" it all ran on battery. There was no infrastructure to power it outside of a few urban centers until the early 1900s. So we used batteries. Until 1866 we had only glass and ceramic jars filled with acid in a liquid form. Georges Leclanché changed all that. More here.

Georges Leclanché did not invent the dry cell. He came up with the idea that led directly toi a number of competing dry cell designs. His is the godfather of them all. His battery consisted of a zinc anode and a manganese dioxide cathode wrapped in a porous material. This unit was then lowered into a jar of water and ammonium chloride solution.The big change here is that ammonium chloride is not an acid, it's a mildly acidic salt. Unlike batteries using hydrochloric or sulfuric acid, the danger here of death or disfigurement was near zero.

Dry cells were still several steps away and didn't catch on immediately. Even 40 years later wet batteries were still available in the Sears catalog. In 1880 when Alfred Niaudet wrote his Elementary Treatise on Electric Batteries, he referred to dry cells as "Dry Piles." This indicated that the idea was new enough the nomenclature wasn't even settled yet. He pointed out an important feature of dry cells. They're not actually dry. They were slightly moist or oily, and that they actually ceased to work if actually dried. He described the first dry cell in 1812 by  Giuseppe Zamboni. It consisted of layers of paper painted with manganese oxide separated by zinc and foil discs. They worked well. In fact for over 170 years, the Oxford Electric Bell has been ringing, and is assumed to be powered by a pair of Zamboni dry piles. As nifty as that is, they are unlike modern common dry cells.

With the Leclanché wet cell, the anode was made from a compound of carbon and manganese dioxide. The cathode was a zinc rod. The cathode was packed into the vessel, and it was filled with the ammonium chloride solution. The liquid acted as an electrolyte producing current to the carbon terminal. His first demonstration model produced about 1.4 volts. This battery was adopted for use with the telegraph, telephone, electric bells and other early powered devices. It was this zinc/carbon combination that was later adapted to manufacture of dry cells. Clark and Muirhead were probably the first to modify the design, and Leclanché himself re-approached it in his "agglomerate" battery which also employed carbon and zinc poles. most modern batteries today use a carbon rod surrounded by a mixture of manganese dioxide and carbon powder. The electrolyte used is a paste of zinc chloride and ammonium chloride dissolved in water, something Leclanché would find very familiar.