Thatthere is charcoal in baking po-wder, and that vinegar and baking powder will make carbonic acid gas were two bits of knowledge imparted to several hundred school girls and boys by Professor Peter T. Austen in the hall of the Brooklyn Polytechnic instituto. This was the second of a series of leotures to young people on "How to Make Scientiflc Experimenta at Home. ' ' Using the siruplest kind of apparatus, Professor Austen demonstrated how carbonic acid gas can be generated from a combination of vinegar and baking powder, and he showed also how the burning oí' a magnesium wire in a jar of carbonic acid gas briugs oat the charcoal in baking powder. The children were intensely interested in the statement that whenever they ate bread or cake made by the use of bakïng powder they ate a lot of charcoal, but they took the lecturer's assertion that there was charcoal in sugar as a joke. "While hot carbonic acid gas is lighter than air, cold carbonic acid gas is niuch heavier than air and can be handled like water, " said Professor Austen. To show the heavy and palpable quality he generated a lot of it in a large glass jar and proceeded to draw it out in cupfuls. Lighted candles were extinguished by pouring the gas upon thein as if it were fluid, and the professor showed his alert disciples how to make carbonic acid gas run through a cardboard trough. A dozen small candles, ligbted, were placed a few inches apart in a long glass channel. From a pitcher Professor Austen slowly poured carbonic acid gas into oue end by the glass chanuel, and as he continued to pour the invisible fluid the lights went out, one by one. The children watched with evident delight the construction of a rnde pair of scales. "I shall use only such things as can be readily picked up around the house, " said the professor. He took a comnion strip of board and planted it upright on his table. Across the top he placed a piece of lath and balanced it exactly by hanging an empty bandbox on one end and a basin of shot on the other. "Now, there is nothing but air in the bandbox," he said. "Let me show you how much heavier carbonio acid gas is than air." And, suiting the action to the word, he poured a large pitcherful of carbonic acid gas into the bandbóx. Immediately the bandbox descended as if filled with bricks. The children applauded and shouted in glee, and a few minutes afterward they were on their way to their homes, imbued with a determination to raid the domestic larder for vinegar and baking powder with which to make bomc acid gas.