Horizontal Axis Interval Help

I am trying to have the intervals spaced out on my horizontal axis so it would depict an accurate relationship between concentration and absorbance, but everything I try is not working. How do I get the chart to have a horizontal axis of 1, 2, 3, 4, etc.? I have tried "intervals between labels" and "intervals between tick marks" but they do not fix the problem.

Here are some screenshots:
http://tinypic.com/r/2u77hcp/8
http://tinypic.com/r/nf67ue/8

I would really appreciate it if someone could help me, thank you!