Final answer:
Thymol is the bacteriostatic chemical used to preserve sediment in urine samples for timed urines. It prevents bacterial growth, ensuring the urine analysis is accurate.
Step-by-step explanation:
The chemical commonly used to preserve sediment in urine samples and that is bacteriostatic for timed urines is thymol (answer c). Toluene (answer b) is incorrectly associated as it is used as a nonpolar solvent in industry and would not have bacteriostatic properties suitable for preserving urine samples. Thymol's bacteriostatic nature helps to prevent bacterial overgrowth in the sample that can alter the results of urine analysis.
As for reference to Exercise 15, the effectiveness of chemical disinfectants has historically been compared to that of phenol. Phenol is a standard by which other disinfectants are measured; this concept is expressed by the 'phenol coefficient' which compares the effectiveness of a disinfectant against phenol when killing specific bacteria like Staphylococcus aureus and Salmonella enterica serovar Typhi.