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AUTOMATIC EQUIPMENT FOR PRECIPITATION WITH H,S S. BARTNISKI GARCIA Escuela Nacional d e Ciencias Biologicas del Instituto Politecnico Nacional, Mexico, D. F., Mexico
T m s precipitation equipment is designed for individual use in qualitative analysis courses. I t can also he used as a small Kipp unit, for the production of carbon dioxide, hydrogen, etc. The apparatus is eronomical, both in the equipment used to build it and in the quantity of HC1 and FeS it consumes. Precipitation with H B is simplified considerably, eliminating the dangerous and noxious H2S smell from the lahoratory. The apparatus can he left ready for use a t any time. The equipment consists of four parts, a description of which follows: (1) Generator. Iron sulfide is placed on glass spheres in the flask, which is then charged with HCI (1 :1) by opening the upper safety tube. A two-holed stopper can he used for the thistle tube, connecting this tube directly to the HC1 source. The acid inflow can he regulated, by means of a pinch clamp or a glass stopcock. The expended HCl can be emptied hy closing
clamp D, waiting until the acid fills the safety tubes, and opening clamp E. (2) Wash bottle. (3) Precipitation flask. Clamp B can he opened to withdraw samples from the flask to determine if the precipitation has been complete. This is done in the following manner: Clamps C and D are left open and A is closed, waiting for the lower safety tube to fill with HC1. Clamp B is slowly opened, the first three drops are discarded, and the amount desired for analysis is then collected. Clamp C is closed, A is opened, and subsequently B is opened long enough to allow the contents of the tube to return to the flask. (4) Safety bottle. This vessel should open to the exterior, through a rubber tube, to a hood or into a sink drain d o w ~which water is running. As a precaution, whenever clamp D is dosed C should also he shut to prevent passage of the contents of the precipitation flask into the wash bottle.
