In Russia, a dozen years later, an aerator was included in a water treatment plant built to supply a government mill on the River Neva at St. Petersburg. The contract to build the plant included pumps, settling reservoirs, an aerator and sand filters. The strainer was made up of four troughs arranged in the form of steps. Each of these was divided longitudinally that did not reach the bottom, into two compartments, the inner one of which was covered by wire gauze, and received the water as it fell from the steps above, and the outer of which contained the horizontal tipped orifices through which the water escaped as it flowed to the step below. Each step was 2 feet high. The lowest step was superposed to one of four sand and gravel filter tanks. After passing downward through filter tanks, the filtered water flowed to deep wells in which it was stored for use. The rated capacity of the treatment plant was 100,000 cubic feet in 10 hours or about 750,000 gallons. Observations on that plant showed that water entered the first step in a perfect lucid state, but before it has passed through two sheets of gauze it became turbid, and deposited black scum on the wire which required constant cleaning, so great was the quanitity of the deposit. In the first filter tank, the water was partially covered with black scum or froth, sometimes more than an inch in thickness, and thin scum, having a metalllic lustre, appeared on the second reservoir.