Abstract: A silica gel of improved hardness and abrasion resistance, increased adsorption power, and other valuable properties is produced by a highly economic process. A useful manufacturing system for making such silica gel and a simple apparatus for producing silica gel spheres of considerably larger diameter than heretofore known are provided.

Abstract: Water is recovered from air by a process utilizing the differences in the day-time and night temperatures of such air. The process is especially useful in subtropical desert areas. It consists in alternately removing the moisture from the cool night air by adsorption on suitable adsorbing agents and especially on silica gel and by utilizing the hot day-time air and, if desired and available, the radiation energy of the sun for desorption of the water stored in the adsorbing agent and for condensing the desorbed water by means of the cold stored during the night. An especially suitable silica gel is used for adsorption of the water contained in the air. The energy required for operating the plant is produced by passing the recovered water through energy producing installations such as turbines before it is used as drinking water or for irrigation. The process is very economical and, in contrast to seawater desalination processes, does not require additional thermal energy.