Therefore, the answer is: prevent liquid from boiling;

(2) The glass conduit used in the device is long, and its function is to condense water vapor;

Therefore, the answer is: condensing water vapor;

(3) The devices for preparing distilled water in the laboratory mentioned in the textbook include: iron stand (with iron ring), asbestos net, alcohol lamp, distillation flask, thermometer, condensing tube, horn tube and conical flask, among which the glass instruments are alcohol lamp, distillation flask, thermometer, condensing tube, horn tube and conical flask.

So the answer is: alcohol lamp, condensing tube, conical bottle,