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Excerpt from The Hot Blast System of Heating and Ventilating: Thesis Submitted in Partial Fulfillment of the Requirements for the Degree of Mechanical Engineer in the Graduate School of the University of Illinois, 1909 When carbonic acid is present in excess of 10 parts in 10000 parts of air, a feeling of weariness and stuffiness, ao companied by a headache, is usually experienced; while even with 8 parts in 10000 parts, a room is considered close. For ade quate ventilation the limit is usually placed at 6 to 7 parts in 10000, thus allowing an increase of 2 to 3 parts per 10000 over that present in outdoor air, which may be considered to contain 4 parts in 10000 under ordinary conditions of a pcpu lous district. About the Publisher Forgotten Books publishes hundreds of thousands of rare and classic books. Find more at www.forgottenbooks.com This book is a reproduction of an important historical work. Forgotten Books uses state-of-the-art technology to digitally reconstruct the work, preserving the original format whilst repairing imperfections present in the aged copy. In rare cases, an imperfection in the original, such as a blemish or missing page, may be replicated in our edition. We do, however, repair the vast majority of imperfections successfully; any imperfections that remain are intentionally left to preserve the state of such historical works.