Two ninth-grade students in the Cuu Long (Mekong) Delta province of Hau Giang have invented an affordable device to assess the level of salt in water.

Le Thi Hong Gam and Le Phuc Hung, students at Phan Van Tri High School, say they applied Archimede’s principle in using plastic balls pumped with salty solution to identify salinity of water.

Experiments in labs showed that the plastic balls sank in pure water and floated on brine. After experimenting in the rivers, the students has developed a tool-kit of nine balls. Firstly, Gam and Hung make the saline solution at the defined ratio, then they inject this solution into the balls and sealed with a glue. Based on Archimede’s principle, they’ve known that the balls will sink in pure water and floated in brine. Experimenting on the rivers shows that if salinity of water inside the ball is equal to salinity of water in river, the ball will stand and the other will continuously moving under the thrust force of water. So that this kit  will help user to know the salinity of water and predict quite exactly the salinity of water.

Lu Thi Hue, a physics teacher who helped  students make the tool, said the device sells for a price of  180,000 VND (US$8) and can be used for three years.

Tran Hoang Anh, a farmer in Tu Sang Village of Tan Tien Commune, said that he has used the device for six months. By observing the balls if they are floating or sinking,  farmers know whether water is salty or not. It helps to identify the time for watering plants.

Nguyen Van Dong, director of the provincial Department of Agriculture and Rural Development, said that salt meters commonly  sell for a price of 1,3 to 2 million VND (equal to 58-89 USD) is too expensive for farmers. The department highly appreciates the device, which is cheap and useful for farmers, especially now there is high salinity in the Mekong Delta’s water.
Source: 3/2016, Tuoitre