LECTURES. 155 



the benches or individual seats. This, however, was not an unmixed 

 gain in the House of Representatives at Wasliington, since the hirge 

 area of occupation necessarily increased the difficulty of hearinj^ and 

 of seeing tlie expressions of countenance during the progress of debate. 



In explaining the estimate sfiven of the amount of air desirable for 

 ventilation, it was stated tliat a temperature of sixty-five to seventy 

 would generally be found most acceptable, and a supply of moisture 

 in the air, such as was indicated l)y a wet-bulb thermometer (the 

 hygrometer in common use) when it showed a temperature live degrees 

 below that of the ordinary thermometer. 



The methods of determining the quality of the air in ventilated 

 apartments then engaged attention. None was so pre-eminently 

 avaihible as that of going out of doors where the atmospliere was })ure, 

 and then comparing the effect there with that of the apartment under 

 examination. Important as this mode was, it was not, however, suf- 

 ficiently precise, nor could it always be put practically in operation 

 with convenience while differences of temperature and a want of sensi- 

 bility in the nostrils, or a loss of the sense of smell from cold, inter- 

 fered with a correct decision. It was a matter of great practical 

 importance, accordingly, that some accessible and convenient test 

 should be available that would at all times and seasons give an indi- 

 cation that would tell the purity of the atmosphere. 



For this purpose Dr. Reid had introduced an instrument called the 

 carbonometer, which was then explained. It admits of a great variety 

 of forms. That shown in action consisted of a bent glass tube attached 

 to a phial containing water, a few droi)S of lime water being placed 

 in the angle of the bent tube. On taking out the stopple from the 

 phial a portion of the water slowly escaped. This caused a flow of 

 air from the apartment under examination through the lime water, 

 which becomes more or less turbid, according to the amount of car- 

 bonic acid in the air. But carbonic acid is invariably present in a 

 very marked proportion in all ordinary atmospheres contaminated by 

 respiration, the combustion of ordinary lamps or candles, f)r the escape 

 of vitiated air from a fire flue. Any excess beyond that in the atmo- 

 sphere renders the amount of lime water used slightly opalescent, 

 milky, or turbid and chalky, according to the amount. Forty speci- 

 mens of air were shown, contaminated with various amounts of car- 

 bonic acid. A syringe may be used instead of a phial of water to 

 cause the movement of air, or a few drops of lime water may be 

 poured into a phial containing air to be examined^ making compara- 

 time ex})eriments with fresh air. 



THIRD LECTURE. 



This lecture was devoted to the warming, cooling, moistening,_ and 

 drying of air, and the exclusion and correction of external vitiated 

 air. 



Great progress had been made in recent years in elucidating many 

 of the properties of heat, in tracing its operation on ditferent kinds 



