FOODS ANIMAL PRODUCTION. 665 



air. The devices for this purpose an- such that the difference of temperature of the 

 incoming and outgoing currents can be kept inside of 0.01° C. In actual experiments 

 the positive and negative differences are made to counterbalance each other." 



The arrange men ts for preventing the passage of heat through the 

 walls of the calorimeter are described as follows: 



" The difference between the temperature of the copper wall and that of the zinc 

 is measured by a system of thermo-electric junctions, in 304 pairs, distributed over 

 the sides, top and bottom, one-half of the junctions (iron-German silver) being in 

 close thermal contact with the copper wall and the other half (German silver-iron) 

 with the zinc wall. The difference of temperature of the two walls is made as small 

 as possible by warming or cooling the air in the space B, and the positive and nega- 

 tive differences are made to counterbalance each other. Thus the corresponding 

 movements of small quantities of heat inward and outward also counterbalance, 

 and the chamber neither gains nor loses heat through the walls. 



"For the measurement of differences of temperature, as well as for the warming 

 and cooling, the walls of the calorimeter are considered as divided into four sections, 

 viz, (1) the top; (2) the upper half of the sides or 'upper zone; ' (3) the lower half 

 of the sides or 'lower zone;' (4) the bottom. The systems of thermo-electric ele- 

 ments for heat measurements, of wires for warming aud of water pipes for cooling, 

 are each divided into corresponding sections." 



The heat carried out by the water current is measured as follows: 



"The principle employed is simple. The chamber neither gains nor loses heat by 

 the air current nor through the walls. The current of cold water which passes 

 through the heat absorbers inside the chamber is caused to enter at a temperature 

 generally but little, above the freezing point, and to flow out at such a rate as to 

 absorb and carry off the heat just as fast as it is generated inside the apparatus. 

 The temperature of the water is measured as it enters and as it comes out. An 

 electrical thermometer indicates the difference of temperature between the incom- 

 ing and outgoing water currents by the difference of resistance of two coils of thin 

 copper wire, of which one is in each pipe at the place of entrance or exit from the 

 calorimeter. The difference is measured by a Wheatstone bridge on the observer's 

 table. The mass of water is measured automatically by apparatus at the right of 

 the window of the respiration chamber. 



"From the mass of the water which has passed through the absorber in a given 

 time and the rise in temperature the quantities of heat brought out are readily 

 calculated. To this is to be added a certain amount of heat w T hich is carried away 

 with the water vapor produced in the apparatus. This is practically the difference 

 between the water vapor in the incoming and outgoing air. From the amount of 

 this vapor, and its latent heat at the temperature of exit, the amount of heat it 

 carries out is easily computed." 



The apparatus for measuring and sampling the ventilating current is 

 described as follows: 



" Three forms of apparatus have been used for maintaining the air current and 

 measuring its volume. One consisted of an ordinary air pump with a meter made by 

 Fister in Berlin. With this we have been unable to make measurements as accurate 

 as seem to us desirable. 



•'For taking samples of air for analysis aspirators of 150 liters capacity were 

 employed at the outset and are still used. The measurements with these have been 

 found quite accurate. The most satisfactory arrangement we have found, and one 

 which serves the threefold purpose oi maintaining the air current, measuring its 



