DuPont (NYSE: DD) tweaked its fourth-quarter earnings outlook this morning. The country's biggest chemical company is still navigating murky economic waters, with high energy costs and weak demand bogging it down.

Earnings for the quarter are now expected to be $0.31-$0.33 a share, slightly less than the company was anticipating. Analysts have been expecting $0.33 a share. According to DuPont, special items won't have a material effect on its bottom line.

What is causing the shortfall, then? Operating results that grew unexpectedly weak in the second half of the Dow component's quarter. Continued slack demand and high oil and natural gas prices are turning the screws on DuPont. And a hoped-for manufacturing pick-up in the fourth quarter just didn't happen.

DuPont did say, however, that the operating issues will be largely offset by the company's ever-declining effective income tax rate. This is the same benefit that helped bolster DuPont's third-quarter earnings by 35%.

In last year's fourth quarter, DuPont earned $0.12 a share. While this year's results will obviously easily top last year's, it doesn't signify a turnaround yet for DuPont's fortunes. It, along with other chemical companies, has been struggling over the last few years. Renewed economic and manufacturing strength should translate into better performance for DuPont... eventually. The company has countered its economic reality by cutting jobs and costs, but it needs business to pick up.

DuPont will give us a better picture of what's going on inside the company when it reports earnings on Jan. 28.