We report optical extinction properties of dust for a sample of 26 early-type galaxies based on the analysis of their multicolour CCD observations .
The wavelength dependence of dust extinction for these galaxies is determined and the extinction curves are found to run parallel to the Galactic extinction curve , which implies that the properties of dust in the extragalactic environment are quite similar to those of the Milky Way .
For the sample galaxies , value of the parameter R _ { V } , the ratio of total extinction in V band to selective extinction in B & V bands , lies in the range 2.03 - 3.46 with an average of 3.02 , compared to its canonical value of 3.1 for the Milky Way .
A dependence of R _ { V } on dust morphology of the host galaxy is also noticed in the sense that galaxies with a well defined dust lane show tendency to have smaller R _ { V } values compared to the galaxies with disturbed dust morphology .
The dust content of these galaxies estimated using total optical extinction is found to lie in the range 10 ^ { 4 } to 10 ^ { 6 } M _ { \sun } , an order of magnitude smaller than those derived from IRAS flux densities , indicating that a significant fraction of dust intermixed with stars remains undetected by the optical method .
We examine the relationship between dust mass derived from IRAS flux and the X-ray luminosity of the host galaxies.The issue of the origin of dust in early-type galaxies is also discussed .