trying to total times

Hello, I have been searching this site for an answer before posting but no joy. What i want to do is add together cells containing times eg cell D174 shows 00:19:03 and cell D175 shows 00:00:58. how do I make cell D180 show 00:20:01. This is just a small example as ultimately i need to add a long column of these sorts of times.
Thank you.

Think I have sorted it. It would appear that the column of times i need to add I imported from another source hence the problem. If however i re-type the info it works.any ideas?

This is the sheet with the column i am trying to add together in cell A174, any ideas why it isn't working?
Workbook3.xls.zip

Each of your times is preceded by a single space. This formula will add them

=SUMPRODUCT(TRIM(A1:A172)+0)

custom format A174 as [h]:mm:ss

the square brackets ensure that hours over 24 can be displayed

You can make the SUM formula work if you select column A and use Edit > Replace to replace a space with nothing

Thanks Daddylonglegs you sorted it. I have also learned something new!
Thanks again