E. M. F. of the entire battery or of single cells may be accurately determined.
2835. Accumulators should not be installed near any apparatus which has bright metal surfaces, such as an engine, as the fumes from the acid will corrode such surfaces unless they are protected by a coating of grease or varnish; all connectors and other brass pieces used around the cell should be coated with varnish or grease for the same reason. Vaseline is especially applicable for this purpose.
This effect may be largely prevented by providing the cells with covers, which also prevents evaporation to a large extent. Covering the liquid with a layer of heavy oil has also been proposed, but this plan involves a great deal of troublesome dirtiness, as the bubbling of the escaping gas causes the oil to spatter.
