60 A RESPIRATION CALORIMETER. 



with the experimental work with the respiration calorimeter. For this 

 reason, where it is necessary to make comparisons of weights and vol- 

 umes of gases, the relations are calculated for the latitude and elevation 

 of the calorimeter laboratory. For similar reasons, weights are not 

 reduced to vacuum. 



THE BAROMETER. 



With the volume of air confined in the apparatus, amounting to about 

 5,000 liters, slight variations in barometric pressure will make relatively 

 large variations in the apparent volume of the air in the system. A 

 variation in barometric pressure of i mm. of mercury, or i part in 760, 

 is accompanied by a variation amounting to about 7 liters in the apparent 

 volume of air. Consequently it is necessary that the barometric pressure 

 be known as accurately as possible. 



Through the kindness of Mr. Willis L. Moore, chief of the Weather 

 Bureau of the United States Department of Agriculture, at Wash- 

 ington, a barometer was loaned for use in connection with these experi- 

 ments. The barometer was brought to Middletown by Prof. Charles 

 F. Marvin, of the instrument division of the Weather Bureau, who 

 personally superintended its installation. This instrument is of the 

 Fortin type, capable of being read with a vernier to o.ooi inch. It is 

 mounted with two white backgrounds, consisting of two sheets of paper, 

 behind which two incandescent lamps are placed. When the lamps are 

 lighted a brilliantly illuminated field gives excellent opportunity for 

 adjusting the vernier at the top. The box in which the barometer is 

 hung is firmly supported on two uprights extending from the floor to 

 the ceiling of the laboratory. The relative position of the barometer 

 to the rest of the apparatus is shown in figure i . 



Tables giving corrections for the barometer and for the attached 

 thermometer were furnished by the U. S. Weather Bureau, and before 

 being brought to Middletown the instrument was carefully adjusted 

 under Professor Marvin's supervision. Its accuracy is all that could be 

 desired. 



The correction for the scale errors and capillarity of this instrument 

 amounts to + 0.002 inch and the correction for local gravity at the 

 latitude of Middletown, 41 34', is 0.009 inch, making the total cor- 

 rection 0.007. As will be noted later, however, it is found to simplify 

 calculations if the corrections for gravity are not applied, and in practice 

 the correction used is -f 002 inch. 



The thermometer attached to the barometer has only insignificant 

 corrections for that portion of the scale on which readings are usually 



