The effect of Me4NI,n-Bu4NI,n-BuEt3NI, Et3PhNI and Et4NBez on the temperature of maximum density of water was determined using a dilatometric technique. The concentration range was from 0.005m to 0.050m in all cases. The temperature data was used to calculate Despretz constants using the equations ΔΦ=Φsot- Φwand ΔΦ=Kmm where Φsot- Φwis the difference between temperature of maximum density of the solution and of water,Kmis the Despretz constant. The equation of Kaulgud and Pokale ΔΦ+1,074m3/2=Kmwas also used.