Aspirator

Aspirator is the name of an apparatus employed to draw air or other gases through bottles or other vessels. It is of great use in the examination of gases by the analytical chemist. The simplest form of the apparatus is that represented in fig. 1, where A is a large vessel capable of being filled with water, having a tube with stopcock at B, a second tube with stopcock at C, and a thermometer introduced at D. In working, the apparatus is filled with water; the tube C is attached to the vessels through which the gas is to be drawn; and the stopcocks at C and B being opened, the weight of the water escaping at B acts as suction, and draws in the gas from the tube C and the attached bottles or other vessels. The thermometer at D denotes the temperature of the water, and subsequently gas, contained in the reservoir, while the upright turn of the tube B keeps any air from entering the reservoir by that route. Another form of aspirator is represented in fig. 2. A is connected with a supply of water under pressure. As the jet of water is forced into the contracted neck at D, it draws the air from B along with it down the outlet pipe C. This form of aspirator is much used in the chemical laboratory for filtering purposes. Into the neck of the funnel is placed a small cone of platinum foil, and thereafter the filtering-paper is carefully fitted. The funnel of the aspirator (or filter-pump) is then passed through an india-rubber cork, fitted to a strong flask, and provided with a tube connecting it with the aspirator. On opening the stopcock B, a partial vacuum is formed in the flask, and the liquid in the filter rapidly passes through.