THE RESPIRATION CALORIMETER. 1043 



made with soldered joints and the al)sorption tubes arc carefull}^ tested 

 with the manometer before ])eino- used. The amount of pkitinized 

 kaolin employed has been demonstrated to be sufficient to oxidize much 

 larger amounts of methane than it will ever be required to in actual use. 

 No parallel determinations of combustible gases are at present made 

 in the air entering the apparatus. The amounts have been shown to 

 be ver}' small in this locality' and corrections are made for them from 

 the results of numerous blanks. 



THE CALORIMETER. 



The arrangements for determining the heat given off by the animal 

 are in all essentials like those of the Atwater-Rosa apparatus. The 

 heat is absorbed by a current of cold water passing through copper 

 pipes at tTie top of the respiration chamber, access of air to these 

 pipes being regulated by means of shields which can be raised or 

 lowered by the operator. The temperature of the ingoing and out- 

 coming Avater is read every four minutes by means of two mercurial 

 thermometers, graduated to 5^0° C. and carefully calibrated. The vol- 

 ume of water passing through is measured by means of two copper 

 meters, each containing 1<H) liters. The apparatus is so arranged that 

 the weight of the heat absorbers ma}^ be taken from outside, any con- 

 densation of moisture upon them being thus indicated. 



The respiration chamber proper of the apparatus is a metallic 

 chamber of the dimensions stated al)ove. Surrounding this, with an 

 airspace of 4 inches between, is a double wooden wall, which in turn is 

 surrounded l)y a second wall and air space of 4 inches. The walls of 

 the respiration chamber proper are doul)le, the inner of copper and the 

 outer of zinc, with a 3-inch dead air space between, and through these 

 walls are distributed some 600 iron German-silver couples connected 

 in series with a reflecting galvanometer and serving to indicate any 

 difference in temperature between the inner (copper) and outer (zinc) 

 surface. Any such difference is rectified and the walls of the chamber 

 maintained adiabatic bv heating or cooling the air space surrounding 

 the zinc wall — the former by means of an electric current through 

 rcsistanc(> wires and the latter ])y circulating cold water through brass 

 pipes (PI. \ll). The double wooden wall surrounding the metallic 

 chamber also contains a smaller number of iron German-silver 

 couples, and is in its turn kept nearly adiabatic by regulating the 

 temY)eiature of the second air space. By means of very similar 

 devices, the temperature of the ingoing air is maintained the same as 

 that of the outcoming air. 



The temperature of the interior of the apparatus is measured l)v 

 means of a series of copper resistance thermometers connected to a 

 slide-wir*^ Wheatstone bridge, and also by means of two mercurial 

 thermometers. B3' raising or lowering the shields or varying the flow 



