A'erostat'ic Press, a simple contrivance for rendering the pressure of the atmosphere available for extracting the coloring matter from dye-woods, and for similar purposes. A horizontal partition divides the machine into two parts. The lower part is connected with an air-pump, by means of which the air can be withdrawn from it. The substance from which the coloring matter is to be extracted is laid upon the partition, which is perforated, and a perforated cover is placed over it. Upon this the liquid intended to form the extract is poured, and as the air is extracted from the lower vessel by the pump, the pressure of the atmosphere forces the liquid through the substance and this extracts the coloring matter.