Figure 7. --Hoist used to lift Figure 8. --Test setup showing hose 



substrate sample. connections and A-frame. 



Temperature Equipment 



A Digitec model 5900 digital thermometer and a six position Omega thermo- 

 couple switch are used to measure the temperature of the downstream probe in each 

 row and of the two thermocouples placed in the substrate sample. The temperature 

 of the downstream probes is needed to insure the C0 2 was in liquid form. 



Sample Transportation 



An insulated boat was built to transport the sample. The floating capacity of 

 the boat is 1,400 lb (635 kg) with a 4-inch (10 cm) freeboard. An improvement needs 

 to be made in transporting the sample by boat because of difficulties in supporting 

 the sample in its original form and transporting it to the loading area. 



OPERATION OF EQUIPMENT 



Three basic cooling mediums were considered for freezing the sample: liquid 

 nitrogen which is difficult to handle, mechanical refrigeration which is expensive, 

 and liquid C0 2 which was accepted as the medium for this method. The liquid C0 2 

 method was tested twice in an artificial stream channel with good results and twice in 

 a salmon spawning area. The first test in the spawning area showed we needed to stop 

 most of the surface flow for good results. The second test showed freezing was easily 

 accomplished by reducing the surface flows. 



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