Also known as manometric fluid. Water strongly adheres to glass so an emulsifier should be added to avoid water droplets “sticking” to the walls of the manometer and so affecting the readings, and to reduce capillary action in small bore manometers. Recipe: 46 g of sodium chloride, 10 g of sodium tauroglycocholate (bile salts), 0.2 g sodium azide (this reagent reduces mould growth), 0.5 g of eosin, 1 litre of pure water. Hazards: Sodium azide is very toxic and contact with acids liberates a very toxic gas. Control measures; once in solution, the risk is minimal. This substance may be omitted but the fluid will not keep as well.