1. The carbonates or hydrated carbonates employed in a large number of industrial and other processes, which are the cause of much lead poisoning. 2. The acetates, both normal and basic, which are particularly concerned in the production of white lead--at any rate in the process of converting metallic lead into the hydrated carbonate through the medium of acetic acid and steam. 3. Chromate of lead, which is used as a pigment, and also in dyeing yarns, etc. 4. The nitrates and chlorides; the chloride particularly is used as an oxidizing agent (plumbing, soldering, tinning of metals). 5. The silicates, silico-borates, silico-fluoborates, which constitute the many varieties of glass and crystals used in optical instruments, and the various glazes and enamel colours used in the potteries. There are a large number of other derivatives, but these are not of special interest to the subject in hand. =The Action of Water upon Lead.=--The action of water on lead was known even to the ancients, Pliny and Galen having written on the subject. At times, and under certain conditions, as much as 20 milligrammes per litre have been found, as in the Bacup epidemic, and 14 milligrammes per litre in the epidemic at Claremont. Bisserie[6] in 1900 made an exhaustive inquiry into the action of water upon lead; he gives the following conclusions: 1. Water and saline solutions attack lead more or less readily when it is in combination with another metal, such as solder, copper, bronze, iron, or nickel, the result being a hydrated oxide. 2. The maximum effect is produced with water slightly acid and with solutions of chlorides or nitrates. With these it is not necessary to have other metals present, and if the water is thoroughly aerated the pure metal is attacked. 3. Bicarbonates and carbonic acid exercise by themselves an action on wet lead, but the carbonate of lead formed in the process adheres firmly to the surface of the metal, and prevents any further action. 4. Sulphates act in the same way, but in less degree. 5. This protective action is much diminished when the water is even slightly charged with nitrates or organic material. Pouchet has pointed out that lead branch-pipes fixed to iron water-pipes, thus producing an “iron-lead couple,” set up definite electro-chemical changes, and tend to increase the rate at which solution of lead in the pipe water takes place.