The following paragraph sketches out a few more details of those results as chronicled in the NASA SP-4212 'On Mars-Exploration of the Red Planet 1958-1978'
The Viking landers used an extendible arm to dig up soil samples and place them in a variety of chambers on the top of the spacecraft for biological and chemical tests. The Gas Exchange Experiment within one chamber detected a release of carbon dioxide and a good deal of oxygen from a soil sample exposed indirectly to moisture, in a manner soon seen as consistent with the presence of peroxides in the iron rich soil. The Labeled Release Experiment added a nutrient solution to another soil sample causing a similar out gassing, consistent with reactions by micro-organisms or of a peroxide rich soil, which didn't repeat when more nutrient was added as might be expected from a growing culture. The Pyrolytic Release Experiment dropped a bit of Mars soil into a chamber mimicking the Martian environment, with added radioactive gases, for five days, after which the little xenon 'sun lamp' within was shut off and the atmosphere pumped out. A little furnace then heated the sample in hopes of detecting radioactive carbon dioxide left over from organisms having ingested the gases added earlier. Very small amounts of such gas were recorded at the Viking 1 site, but not at Viking 2. In the event of ambiguous results from the trio of biology experiments, the GCMS (Gas Chromatagraph-Mass Spectrometer) was to provide the final 'court of appeals'. Although a surprising amount of water was released as a soil sample was then heated to 500 degrees C, the soil was found by the GCMS to be devoid of organic molecules to its detection limits. A chemical process was thus invoked as explaining the results obtained by the biology experiments rather than make a risky declaration of something as momentous as finding life on Mars based on such ambiguous experimental results.